$\\Lambda$CDM-type cosmological model and observational constraints
Goswami, G K; Mishra, Mandwi
2014-01-01
In the present work, we have searched the existence of $\\Lambda$CDM-type cosmological model in anisotropic Heckmann-Schucking space-time. The matter source that is responsible for the present acceleration of the universe consist of cosmic fluid with $p = \\omega\\rho$, where $\\omega$ is the equation of state parameter. The Einstein's field equations have been solved explicitly under some specific choice of parameters that isotropizes the model under consideration. It has been found that the derived model is in good agreement with recent SN Ia observations. Some physical aspects of the model has been discussed in detail.
Constraining the $\\Lambda$CDM and Galileon models with recent cosmological data
Neveu, J; Astier, P; Besançon, M; Guy, J; Möller, A; Babichev, E
2016-01-01
The Galileon theory belongs to the class of modified gravity models that can explain the late-time accelerated expansion of the Universe. In previous works, cosmological constraints on the Galileon model were derived, both in the uncoupled case and with a disformal coupling of the Galileon field to matter. There, we showed that these models agree with the most recent cosmological data. In this work, we used updated cosmological data sets to derive new constraints on Galileon models, including the case of a constant conformal Galileon coupling to matter. We also explored the tracker solution of the uncoupled Galileon model. After updating our data sets, especially with the latest \\textit{Planck} data and BAO measurements, we fitted the cosmological parameters of the $\\Lambda$CDM and Galileon models. The same analysis framework as in our previous papers was used to derive cosmological constraints, using precise measurements of cosmological distances and of the cosmic structure growth rate. We showed that all te...
La Fin du MOND? {\\Lambda} CDM is Fully Consistent with SPARC Acceleration Law
Keller, B W
2016-01-01
Recent analysis (McGaugh et al. 2016) of the SPARC galaxy sample found a surprisingly tight relation between the radial acceleration inferred from the rotation curves, and the acceleration due to the baryonic components of the disc. It has been suggested that this relation may be evidence for new physics, beyond {\\Lambda}CDM . In this letter we show that the 18 galaxies from the MUGS2 match the SPARC acceleration relation. These cosmological simulations of star forming, rotationally supported discs were simulated with a WMAP3 {\\Lambda}CDM cosmology, and match the SPARC acceleration relation with less scatter than the observational data. These results show that this acceleration law is a consequence of dissipative collapse of baryons, rather than being evidence for exotic dark-sector physics or new dynamical laws.
Accelerating Cosmologies from Compactification
Townsend, P K; Townsend, Paul K.; Wohlfarth, Mattias N.R.
2003-01-01
A solution of the (4+n)-dimensional vacuum Einstein equations is found for which spacetime is compactified on a compact hyperbolic manifold of time-varying volume to a flat four-dimensional FLRW cosmology undergoing accelerated expansion in Einstein conformal frame. This shows that the `no-go' theorem forbidding acceleration in `standard' (time-independent) compactifications of string/M-theory does not apply to `cosmological' (time-dependent) hyperbolic compactifications.
$\\sigma$CDM coupled to radiation. Dark energy and Universe acceleration
Abbyazov, Renat R; Müller, Volker
2014-01-01
Recently the Chiral Cosmological Model (CCM) coupled to cold dark matter (CDM) has been investigated as $\\sigma$CDM model to study the observed accelerated expansion of the Universe. Dark sector fields (as Dark Energy content) coupled to cosmic dust were considered as the source of Einstein gravity in Friedmann-Robertson-Walker (FRW) cosmology. Such model had a beginning at the matter-dominated era. The purposes of our present investigation are two folds: to extend > of the $\\sigma$CDM for earlier times to radiation-dominated era and to take into account variation of the exponential potential via variation of the interaction parameter $\\lambda $. We use Markov Chain Monte Carlo (MCMC) procedure to investigate possible values of initial conditions constrained by the measured amount of the dark matter, dark energy and radiation component today. Our analysis includes dark energy contribution to critical density, the ratio of the kinetic and potential energies, deceleration parameter, effective equation of state ...
Gamma-ray bursts as cosmological probes: LambdaCDM vs. conformal gravity
Diaferio, Antonaldo; Cardone, Vincenzo F
2011-01-01
LambdaCDM, for the currently preferred cosmological density Omega_0 and cosmological constant Omega_Lambda, predicts that the Universe expansion decelerates down to redshift z~0.9 and accelerates at later times. On the contrary, the cosmological model based on conformal gravity predicts that the cosmic expansion has always been accelerating. To distinguish between these two very different cosmologies, we resort to gamma-ray bursts (GRBs), which have been suggested to probe the Universe expansion history at z>1, where identified type Ia supernovae (SNe) are rare. We use the full Bayesian approach to infer the cosmological parameters and the additional parameters required to describe the GRB data available in the literature. For the first time, we use GRBs as cosmological probes without any prior information from other data. In addition, when we combine the GRB samples with SNe, our approach neatly avoids all the inconsistencies of most numerous previous methods that are plagued by the so-called circularity pro...
Cosmological acceleration. Dark energy or modified gravity?
International Nuclear Information System (INIS)
We review the evidence for recently accelerating cosmological expansion or ''dark energy'', either a negative pressure constituent in General Relativity (Dark Energy) or modified gravity (Dark Gravity), without any constituent Dark Energy. If constituent Dark Energy does not exist, so that our universe is now dominated by pressure-free matter, Einstein gravity must be modified at low curvature. The vacuum symmetry of any Robertson-Walker universe then characterizes Dark Gravity as low- or high-curvature modifications of Einstein gravity. The dynamics of either kind of ''dark energy'' cannot be derived from the homogeneous expansion history alone, but requires also observing the growth of inhomogeneities. Present and projected observations are all consistent with a small fine tuned cosmological constant, but also allow nearly static Dark Energy or gravity modified at cosmological scales. The growth of cosmological fluctuations will potentially distinguish between static and ''dynamic'' ''dark energy''. But, cosmologically distinguishing the Concordance Model ΛCDM from modified gravity will require a weak lensing shear survey more ambitious than any now projected. Dvali-Gabadadze-Porrati low-curvature modifications of Einstein gravity may also be detected in refined observations in the solar system (Lue and Starkman) or at the intermediate Vainstein scale (Iorio) in isolated galaxy clusters. Dark Energy's epicyclic character, failure to explain the original Cosmic Coincidence (''Why so small now?'') without fine tuning, inaccessibility to laboratory or solar system tests, along with braneworld theories, now motivate future precision solar system, Vainstein-scale and cosmological-scale studies of Dark Gravity. (Orig.)
Simulating cosmologies beyond $\\Lambda$CDM with PINOCCHIO
Rizzo, Luca Alberto; Monaco, Pierluigi; Munari, Emiliano; Borgani, Stefano; Castorina, Emanuele; Sefusatti, Emiliano
2016-01-01
We present a method that extends the capabilities of the PINpointing Orbit-Crossing Collapsed HIerarchical Objects (PINOCCHIO) code, allowing it to generate accurate dark matter halo mock catalogues in cosmological models where the linear growth factor and the growth rate depend on scale. Such cosmologies comprise, among others, models with massive neutrinos and some classes of modified gravity theories. We validate the code by comparing the halo properties from PINOCCHIO against N-body simulations, focusing on cosmologies with massive neutrinos: $\
Little Rip, ΛCDM and singular dark energy cosmology from Born–Infeld-f(R) gravity
International Nuclear Information System (INIS)
We study late-time cosmic accelerating dynamics from Born–Infeld-f(R) gravity in a simplified conformal approach. We find that a variety of cosmic effects such as Little Rip, ΛCDM universe and dark energy cosmology with finite-time future singularities may occur. Unlike the convenient Born–Infeld gravity where in the absence of matter only de Sitter expansion may emerge, apparently any FRW cosmology maybe reconstructed from this conformal version of the Born–Infeld-f(R) theory. Despite the fact that the explicit form of f(R) is fixed by the conformal ansatz, the relation between the two metrics in this approach may be changed so as to bring out any desired FRW cosmology
Where the world stands still: turnaround as a strong test of ΛCDM cosmology
Energy Technology Data Exchange (ETDEWEB)
Pavlidou, V.; Tomaras, T.N., E-mail: pavlidou@physics.uoc.gr, E-mail: tomaras@physics.uoc.gr [Department of Physics and ITCP, University of Crete, 71003 Heraklion (Greece)
2014-09-01
Our intuitive understanding of cosmic structure formation works best in scales small enough so that isolated, bound, relaxed gravitating systems are no longer adjusting their radius; and large enough so that space and matter follow the average expansion of the Universe. Yet one of the most robust predictions of ΛCDM cosmology concerns the scale that separates these limits: the turnaround radius, which is the non-expanding shell furthest away from the center of a bound structure. We show that the maximum possible value of the turnaround radius within the framework of the ΛCDM model is, for a given mass M, equal to (3GM/Λ c{sup 2}){sup 1/3}, with G Newton's constant and c the speed of light, independently of cosmic epoch, exact nature of dark matter, or baryonic effects. We discuss the possible use of this prediction as an observational test for ΛCDM cosmology. Current data appear to favor ΛCDM over alternatives with local inhomogeneities and no Λ. However there exist several local-universe structures that have, within errors, reached their limiting size. With improved determinations of their turnaround radii and the enclosed mass, these objects may challenge the limit and ΛCDM cosmology.
Cosmological constant vis-à-vis dynamical vacuum: Bold challenging the ΛCDM
Solà, Joan
2016-08-01
Next year we will celebrate 100 years of the cosmological term, Λ, in Einstein’s gravitational field equations, also 50 years since the cosmological constant problem was first formulated by Zeldovich, and almost about two decades of the observational evidence that a nonvanishing, positive, Λ-term could be the simplest phenomenological explanation for the observed acceleration of the Universe. This mixed state of affairs already shows that we do no currently understand the theoretical nature of Λ. In particular, we are still facing the crucial question whether Λ is truly a fundamental constant or a mildly evolving dynamical variable. At this point the matter should be settled once more empirically and, amazingly enough, the wealth of observational data at our disposal can presently shed true light on it. In this short review, I summarize the situation of some of these studies. It turns out that the Λ = const. hypothesis, despite being the simplest, may well not be the most favored one when we put it in hard-fought competition with specific dynamical models of the vacuum energy. Recently, it has been shown that the overall fit to the cosmological observables SNIa+BAO+H(z)+LSS+BBN+CMB do favor the class of “running” vacuum models (RVM’s) — in which Λ = Λ(H) is a function of the Hubble rate — against the “concordance” ΛCDM model. The support is at an unprecedented level of ˜ 4σ and is backed up with Akaike and Bayesian criteria leading to compelling evidence in favor of the RVM option and other related dynamical vacuum models. I also address the implications of this framework on the possible time evolution of the fundamental constants of Nature.
Cosmological acceleration. Dark energy or modified gravity?
Energy Technology Data Exchange (ETDEWEB)
Bludman, S.
2006-05-15
We review the evidence for recently accelerating cosmological expansion or ''dark energy'', either a negative pressure constituent in General Relativity (Dark Energy) or modified gravity (Dark Gravity), without any constituent Dark Energy. If constituent Dark Energy does not exist, so that our universe is now dominated by pressure-free matter, Einstein gravity must be modified at low curvature. The vacuum symmetry of any Robertson-Walker universe then characterizes Dark Gravity as low- or high-curvature modifications of Einstein gravity. The dynamics of either kind of ''dark energy'' cannot be derived from the homogeneous expansion history alone, but requires also observing the growth of inhomogeneities. Present and projected observations are all consistent with a small fine tuned cosmological constant, but also allow nearly static Dark Energy or gravity modified at cosmological scales. The growth of cosmological fluctuations will potentially distinguish between static and ''dynamic'' ''dark energy''. But, cosmologically distinguishing the Concordance Model {lambda}CDM from modified gravity will require a weak lensing shear survey more ambitious than any now projected. Dvali-Gabadadze-Porrati low-curvature modifications of Einstein gravity may also be detected in refined observations in the solar system (Lue and Starkman) or at the intermediate Vainstein scale (Iorio) in isolated galaxy clusters. Dark Energy's epicyclic character, failure to explain the original Cosmic Coincidence (''Why so small now?'') without fine tuning, inaccessibility to laboratory or solar system tests, along with braneworld theories, now motivate future precision solar system, Vainstein-scale and cosmological-scale studies of Dark Gravity. (Orig.)
Conformal Transformations and Accelerated Cosmologies
Crooks, James L.; Frampton, Paul H.
2006-01-01
A cosmological theory that predicts a late-time accelerated attractor with a constant dark matter to dark energy ratio can be said to solve the Coincidence Problem. Such cosmologies are naturally generated in the context of non-standard gravity theories under conformal transformation because of the resulting couplings between scalar fields and matter. The present work examines four classes of these transformed theories and finds that only a small subset--those with a single scalar field--are ...
Consistency of the Planck CMB data and $\\Lambda$CDM cosmology
Shafieloo, Arman
2016-01-01
We test the consistency between Planck temperature and polarization power spectra and the concordance model of $\\Lambda$ Cold Dark Matter cosmology ($\\Lambda$CDM) within the framework of Crossing statistics. We find that Planck TT best fit $\\Lambda$CDM power spectrum is completely consistent with EE power spectrum data while EE best fit $\\Lambda$CDM power spectrum is not consistent with TT data. However, this does not point to any systematic or model-data discrepancy since in the Planck EE data, uncertainties are much larger compared to the TT data. We also investigate the possibility of any deviation from $\\Lambda$CDM model analyzing the Planck 2015 data. Results from both TT and EE data analysis indicate that no deviation is required beyond the flexibility of the concordance $\\Lambda$CDM model. Our analysis thus rules out any strong evidence for beyond the concordance model in the Planck spectra data. We also report a mild amplitude difference comparing temperature and polarization data, where temperature d...
On the Onset of Stochasticity in $\\Lambda$CDM Cosmological Simulations
Thiebaut, Jerome; Pichon, Christophe; Sousbie, Thierry; Prunet, Simon; Pogosyan, D.
2008-01-01
11 pages, 10 figures. Accepted for publication, MNRAS. The onset of stochasticity is measured in $\\Lambda$CDM cosmological simulations using a set of classical observables. It is quantified as the local derivative of the logarithm of the dispersion of a given observable (within a set of different simulations differing weakly through their initial realization), with respect to the cosmic growth factor. In an Eulerian framework, it is shown here that chaos appears at small scales, where dyna...
CMB Lensing as a probe of beyond ΛCDM Cosmology
Hassani, F.; Baghram, S.; Firouzjahi, H.
2016-09-01
The observation of the Cosmic Microwave Background Radiation (CMB) and the Large Structures indicate that the standard model of Cosmology known as ΛCDM works well. In this essay we propose that the CMB lensing is a prominent probe to study any deviation from this model. Deviations from cosmological constant and nearly Gaussian, adiabatic, nearly scale invariant and isotropic initial conditions can be studied by CMB lensing. We show how the angular power spectrum of CMB lensing potential is an observable which encapsulates the effect of initial conditions and Dark Energy. The amplitude and the scale dependence of a dipole modulation in initial conditions is studied with CMB lensing potential and convergence.
Learn-As-You-Go Acceleration of Cosmological Parameter Estimates
Aslanyan, Grigor; Price, Layne C
2015-01-01
Cosmological analyses can be accelerated by approximating slow calculations using a training set, which is either precomputed or generated dynamically. However, this approach is only safe if the approximations are well understood and controlled. This paper surveys issues associated with the use of machine-learning based emulation strategies for accelerating cosmological parameter estimation. We describe a learn-as-you-go algorithm that is implemented in the Cosmo++ code and (1) trains the emulator while simultaneously estimating posterior probabilities; (2) identifies unreliable estimates, computing the exact numerical likelihoods if necessary; and (3) progressively learns and updates the error model as the calculation progresses. We explicitly describe and model the emulation error and show how this can be propagated into the posterior probabilities. We apply these techniques to the Planck likelihood and the calculation of $\\Lambda$CDM posterior probabilities. The computation is significantly accelerated wit...
Downsizing of galaxies vs upsizing of dark-halos in a Lambda-CDM cosmology
De Rossi, Maria E; Gonzalez-Samaniego, Alejandro; Pedrosa, Susana
2013-01-01
The mass assembly of a whole population of sub-Milky Way galaxies is studied by means of hydrodynamical simulations within the $\\Lambda$-CDM cosmology. Our results show that while dark halos assemble hierarchically, in stellar mass this trend is inverted in the sense that the smaller the galaxy, the later is its stellar mass assembly on average. Our star formation and supernovae feedback implementation in a multi-phase interstellar medium seems to play a key role on this process. However, the obtained downsizing trend is not yet as strong as observations show.
D-class of dark energy against $\\Lambda$CDM in Brans-Dicke cosmology
Khodam-Mohammadi, A
2016-01-01
Three general models of dynamical interacting dark energy (D-class) are investigated in the context of Brans-Dicke cosmology. All cosmological quantities such as equation of state parameters, deceleration parameters, Hubble function, and the density ratio are calculated as a function of redshift parameter. The most important part of this paper is fitting of models to the observational data (SNIa+BAO$_A$+$Omh^{2}$). We obtain a table of best fit value of parameters and report $\\chi_{tot}^2/dof$ and Akaike Information Criterion (AIC) for each model. By these diagnostic tools, we find that some models have no chance against $\\Lambda$CDM and some (e.g. $\\mathcal{BD-D}C2$ and $\\mathcal{BD-D}A^*$) render the best fit quality. Specially, the value of AIC analysis and figures show that the interacting $\\mathcal{BD-D}C2$ model fit perfectly with overall data and reveals a strong evidence in favor of this model, against $\\Lambda$CDM.
On the solutions to accelerating cosmologies
Ito, M
2003-01-01
Motivated by recent accelerating cosmological model, we derive the solutions to vacuum Einstein equation in $(d+1)$-dimensional Minkowski space with $n$-dimensional hyperbolic manifold. The conditions of accelerating expansion are given in such a set up.
Formation of Milky Way-type stellar haloes in a Λ-CDM cosmology
Directory of Open Access Journals (Sweden)
Font A.S.
2012-02-01
Full Text Available Recent observations suggest that the Milky Way stellar halo has a ‘dual nature’, meaning that both dissipational and dissipationless processes play a role in its build-up. The GIMIC suite of cosmological hydro-dynamical simulations show that, for Milky Way-mass haloes, in situ star formation is the dominant factor in the inner < 20 − 30 kpc, while tidal disruption of satellite galaxies contributes primarily to the outer regions. The in situ stars are found to originate in the earlier disc, at redshifts ~ 1– 1.5, and subsequently diffusing out of the disc by dynamical heating associated with mergers. The in situ component has a more flattened shape, a net prograde rotation and more metal-rich populations, in quantitative agreement with the observations. We conclude that the dual nature of the stellar halo is entirely compatible with the currently favoured Λ-CDM model.
Ghost-free F(R) bigravity and accelerating cosmology
Energy Technology Data Exchange (ETDEWEB)
Nojiri, Shin' ichi, E-mail: nojiri@phys.nagoya-u.ac.jp [Department of Physics, Nagoya University, Nagoya 464-8602 (Japan); Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Nagoya 464-8602 (Japan); Odintsov, Sergei D., E-mail: odintsov@ieec.uab.es [Consejo Superior de Investigaciones Cientificas, ICE/CSIC-IEEC, Campus UAB, Facultat de Ciencies, Torre C5-Parell-2a pl, E-08193 Bellaterra, Barcelona (Spain); Institucio Catalana de Recerca i Estudis Avancats (ICREA), Barcelona (Spain); Eurasian National University, Astana (Kazakhstan); TSPU, Tomsk (Russian Federation)
2012-09-19
We propose a bigravity analogue of the F(R) gravity. Our construction is based on recent ghost-free massive bigravity where additional scalar fields are added and the corresponding conformal transformation is implemented. It turns out that F(R) bigravity is easier to formulate in terms of the auxiliary scalars as the explicit presentation in terms of F(R) is quite cumbersome. The consistent cosmological reconstruction scheme of F(R) bigravity is developed in detail, showing the possibility to realize nearly arbitrary physical universe evolution with consistent solution for second metric. The examples of accelerating universe which includes phantom, quintessence and {Lambda}CDM acceleration are worked out in detail and their physical properties are briefly discussed.
Dereli, Tekin; Akarsu, Özgür
2013-01-01
arXiv:1201.4545v3 [gr-qc] 31 Mar 2013 A four-dimensional CDM-type cosmological model induced from higher dimensions using a kinematical constraint Özgür Akarsu, Tekin Dereli Department of Physics, Koç University, 34450 Sarıyer, İstanbul, Turkey Abstract A class of cosmological solutions of higher dimensional Einstein field equations with the energy-momentum tensor of a homogeneous, isotropic fluid as the source are considered with an anisotropic metric that includes t...
Accelerating cosmologies from compactification with a twist
International Nuclear Information System (INIS)
It is demonstrated by explicit solutions of the (4+n)-dimensional vacuum Einstein equations that accelerating cosmologies in the Einstein conformal frame can be obtained by a time-dependent compactification of string/M-theory, even in the case that internal dimensions are Ricci-flat, provided one includes one or more geometric twists. Such acceleration is transient. When both compact hyperbolic internal spaces and geometric twists are included, however, the period of accelerated expansion may be made arbitrarily large
Accelerating cosmologies from compactification with a twist
Energy Technology Data Exchange (ETDEWEB)
Neupane, Ishwaree P. [Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch (New Zealand) and Central Department of Physics, Tribhuvan University, Kirtipur, Kathmandu (Nepal)]. E-mail: ishwaree.neupane@canterbury.ac.nz; Wiltshire, David L. [Central Department of Physics, Tribhuvan University, Kirtipur, Kathmandu (Nepal)]. E-mail: d.wiltshire@canterbury.ac.nz
2005-07-21
It is demonstrated by explicit solutions of the (4+n)-dimensional vacuum Einstein equations that accelerating cosmologies in the Einstein conformal frame can be obtained by a time-dependent compactification of string/M-theory, even in the case that internal dimensions are Ricci-flat, provided one includes one or more geometric twists. Such acceleration is transient. When both compact hyperbolic internal spaces and geometric twists are included, however, the period of accelerated expansion may be made arbitrarily large.
Accelerating cosmology in Rastall's theory
Capone, Monica; Ruggiero, Matteo Luca
2009-01-01
In an attempt to look for a viable mechanism leading to a present day accelerated expansion, we investigate the possibility that the observed cosmic speed up may be recovered in the framework of the Rastall's theory, relying on the non - conservativity of the stress - energy tensor, i.e. $T^{\\mu}_{\
Cosmological Acceleration from Gravitational Waves
Marochnik, Leonid
2015-01-01
It is shown that the classical gravitational waves of super-horizon wavelengths are able to form the de Sitter accelerated expansion of the empty (with no matter fields) Universe. The contemporary Universe is about 70% empty and asymptotically is going to become completely empty, so the effect caused by emptiness should be already very noticeable. It could manifest itself as the dark energy.
Cosmological Acceleration: Dark Energy or Modified Gravity?
Bludman, Sidney
2006-01-01
We review the evidence for recently accelerating cosmological expansion or "dark energy", either a negative pressure constituent in General Relativity (Dark Energy) or modified gravity (Dark Gravity), without any Dark Energy constituent. If constituent Dark Energy does not exist, so that our universe is now dominated by pressure-free matter, Einstein gravity must be modified at low curvature. The vacuum symmetry of any Robertson-Walker universe then characterizes Dark Gravity as low- or high-...
Diffusive Shock Acceleration at Cosmological Shock Waves
Kang, Hyesung; Ryu, Dongsu
2012-01-01
We reexamine nonlinear diffusive shock acceleration (DSA) at cosmological shocks in the large scale structure of the Universe, incorporating wave-particle interactions that are expected to operate in collisionless shocks. Adopting simple phenomenological models for magnetic field amplification (MFA) by cosmic-ray (CR) streaming instabilities and Alfv'enic drift, we perform kinetic DSA simulations for a wide range of sonic and Alfv'enic Mach numbers and evaluate the CR injection fraction and a...
Observed Cosmological Redshifts Support Contracting Accelerating Universe
Vlahovic, Branislav
2012-01-01
The main argument that Universe is currently expanding is observed redshift increase by distance. However, this conclusion may not be correct, because cosmological redshift depends only on the scaling factors, the change in the size of the universe during the time of light propagation and is not related to the speed of observer or speed of the object emitting the light. An observer in expanding universe will measure the same redshift as observer in contracting universe with the same scaling. This was not taken into account in analysing the SN Ia data related to the universe acceleration. Possibility that universe may contract, but that the observed light is cosmologically redshifted allows for completely different set of cosmological parameters $\\Omega_M, \\Omega_{\\Lambda}$, including the solution $\\Omega_M=1, \\Omega_{\\Lambda}=0$. The contracting and in the same time accelerating universe explains observed deceleration and acceleration in SN Ia data, but also gives significantly larger value for the age of the...
Hierarchy of N-point functions in the Lambda CDM and ReBEL cosmologies
Hellwing, Wojciech A.; Juszkiewicz, Roman; van de Weijgaert, Marinus
2010-01-01
In this work we investigate higher-order statistics for the Lambda CDM and ReBEL scalar-interacting dark matter models by analyzing 180h(-1) Mpc dark matter N-body simulation ensembles. The N-point correlation functions and the related hierarchical amplitudes, such as skewness and kurtosis, are comp
Meyer, Sven; Pace, Francesco; Bartelmann, Matthias
2012-01-01
Spherical collapse has turned out to be a successful semi-analytic model to study structure formation in different DE models and theories of gravity. Nevertheless, the process of virialization is commonly studied on the basis of the virial theorem of classical mechanics. In the present paper, a fully generally-relativistic virial theorem based on the Tolman-Oppenheimer-Volkoff (TOV) solution for homogeneous, perfect-fluid spheres is constructed for the Einstein-de Sitter and \\Lambda CDM cosmo...
Altamirano-Dévora, L; Aceves, H; Castro, A; Cañas, R; Tamayo, F
2015-01-01
Motivated by recent inferred form of the halo occupation distribution (HOD) of X-ray selected AGNs, in the COSMOS field by Allevato et al. (2012), we investigate the HOD properties of moderate X-ray luminosity Active Galactic Nuclei (mXAGNs) using a simple model based on merging activity between dark matter halos (DMHs) in a $\\Lambda$-CDM cosmology. The HODs and number densities of the simulated mXAGNs at $z=0.5$, under the above scenarios to compare with Allevato et al. (2012) results. We find that the simulated HODs of major and minor mergers, and the observed for mXAGNs are consistent among them. Our main result is that minor mergers, contrary to what one might expect, can play an important role in activity mAGNs.
Forero-Romero, J E; Yepes, G; Gottoeber, S; Piontek, R; Klypin, A; Steinmetz, M
2011-01-01
We make detailed theoretical predictions for the assembly properties of the Local Group (LG) in the standard LambdaCDM cosmological model. We use three cosmological N-body dark matter simulations from the CLUES project, which are designed to reproduce the main dynamical features of the matter distribution down to the scale of a few Mpc around the LG. Additionally, we use the results of an unconstrained simulation with a sixty times larger volume to calibrate the influence of cosmic variance. We characterize the Mass Aggregation History (MAH) for each halo by three characteristic times, the formation, assembly and last major merger times. A major merger is defined by a minimal mass ratio of 10:1. We find that the three LGs share a similar MAH with formation and last major merger epochs placed on average \\approx 10 - 12 Gyr ago. Between 12% and 17% of the halos in the mass range 5 x 10^11 Msol/h < M_h < 5 x 10^12 Msol/h have a similar MAH. In a set of pairs of halos within the same mass range, a fraction ...
A new model for the satellites of the Milky Way in the Lambda CDM cosmology
Font, Andreea S; Bower, Richard G; Frenk, Carlos F; Cooper, Andrew P; De Lucia, Gabriella; Helly, John C; Helmi, Amina; Li, Yang-Shyang; McCarthy, Ian G; Navarro, Julio F; Springel, Volker; Starkenburg, Else; Wang, Jie
2011-01-01
We present a new model for the satellites of the Milky Way in which galaxy formation is followed using semi-analytic techniques applied to the six high-resolution N-body simulations of galactic halos of the Aquarius project. The model, calculated using the GALFORM code, incorporates improved treatments of the relevant physics in the Lambda CDM cosmogony, particularly a self-consistent calculation of reionization by UV photons emitted by the forming galaxy population, including the progenitors of the central galaxy. Along the merger tree of each halo, the model calculates gas cooling (by Compton scattering off cosmic microwave background photons, molecular hydrogen and atomic processes), gas heating (from hydrogen photoionization and supernova energy), star formation and evolution. The evolution of the intergalactic medium is followed simultaneously with that of the galaxies. Star formation in the more massive progenitor subhalos is suppressed primarily by supernova feedback, while for smaller subhalos it is s...
Zhao, Ming-Ming; Zhang, Xin
2016-01-01
We investigate how the properties of dark energy affect the cosmological measurements of neutrino mass and extra relativistic degrees of freedom. We limit ourselves to the most basic extensions of $\\Lambda$CDM model, i.e., the $w$CDM model with one additional parameter $w$, and the $w_{0}w_{a}$CDM model with two additional parameters, $w_{0}$ and $w_{a}$. In the cosmological fits, we employ the 2015 CMB temperature and polarization data from the Planck mission, in combination with low-redshift measurements such as the baryon acoustic oscillations (BAO), type Ia supernovae (SN) and the Hubble constant ($H_{0}$). Given effects of massive neutrinos on large-scale structure, we further include weak lensing (WL), redshift space distortion (RSD), Sunyaev-Zeldovich cluster counts (SZ), and Planck lensing data. We find that $w$ is anti-correlated with $\\sum m_{\
The Planck legacy - Reinforcing the case for a standard model of cosmology: $\\Lambda$CDM
Mandolesi, Nazzareno; Gruppuso, Alessandro; Burigana, Carlo; Natoli, Paolo
2016-01-01
We present a brief review of the main results of the Planck 2015 release describing the new calibration of the data, showing the maps delivered in temperature and, for the first time, in polarization, the cosmological parameters and the lensing potential. In addition we present a forecast of the Galactic foregrounds in polarization. Future satellite experiments will have the challenge to remove the foregrounds with great accuracy to be able to measure a tensor-to-scalar ratio of less than 0.01.
Discovery of a Supercluster at $z\\sim$0.91 and Testing the $\\Lambda$CDM Cosmological Model
Kim, J -W; Lee, S -K; Edge, A C; Hyun, M; Kim, D; Choi, C; Hong, J; Jeon, Y; Jun, H D; Karouzos, M; Kim, D; Kim, J H; Kim, Y; Park, W -K; Taak, Y C; Yoon, Y
2016-01-01
The $\\Lambda$CDM cosmological model successfully reproduces many aspects of the galaxy and structure formation of the universe. However, the growth of large-scale structures (LSSs) in the early universe is not well tested yet with observational data. Here, we have utilized wide and deep optical--near-infrared data in order to search for distant galaxy clusters and superclusters ($0.8
Local and non-local measures of acceleration in cosmology
Bull, Philip
2012-01-01
Current cosmological observations, when interpreted within the framework of a homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker (FLRW) model, strongly suggest that the Universe is entering a period of accelerating expansion. This is often taken to mean that the expansion of space itself is accelerating. In a general spacetime, however, this is not necessarily true. We attempt to clarify this point by considering a handful of local and non-local measures of acceleration in a variety of inhomogeneous cosmological models. Each of the chosen measures corresponds to a theoretical or observational procedure that has previously been used to study acceleration in cosmology, and all measures reduce to the same quantity in the limit of exact spatial homogeneity and isotropy. In statistically homogeneous and isotropic spacetimes, we find that the acceleration inferred from observations of the distance-redshift relation is closely related to the acceleration of the spatially averaged universe, but does not ne...
A TWO-PHASE SCENARIO FOR BULGE ASSEMBLY IN {Lambda}CDM COSMOLOGIES
Energy Technology Data Exchange (ETDEWEB)
Obreja, A.; Dominguez-Tenreiro, R.; Brook, C. [Departamento de Fisica Teorica, Universidad Autonoma de Madrid, E-28049 Cantoblanco Madrid (Spain); Martinez-Serrano, F. J.; Domenech-Moral, M.; Serna, A. [Departamento de Fisica y Arquitectura de Computadores, Universidad Miguel Hernandez, E-03202 Elche (Spain); Molla, M. [Departamento de Investigacion Basica, CIEMAT, E-28040 Madrid (Spain); Stinson, G., E-mail: aura.obreja@uam.es [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117, Heidelberg (Germany)
2013-01-20
We analyze and compare the bulges of a sample of L {sub *} spiral galaxies in hydrodynamical simulations in a cosmological context, using two different codes, P-DEVA and GASOLINE. The codes regulate star formation in very different ways, with P-DEVA simulations inputting low star formation efficiency under the assumption that feedback occurs on subgrid scales, while the GASOLINE simulations have feedback that drives large-scale outflows. In all cases, the marked knee shape in mass aggregation tracks, corresponding to the transition from an early phase of rapid mass assembly to a later slower one, separates the properties of two populations within the simulated bulges. The bulges analyzed show an important early starburst resulting from the collapse-like fast phase of mass assembly, followed by a second phase with lower star formation, driven by a variety of processes such as disk instabilities and/or mergers. Classifying bulge stellar particles identified at z = 0 into old and young according to these two phases, we found bulge stellar sub-populations with distinct kinematics, shapes, stellar ages, and metal contents. The young components are more oblate, generally smaller, more rotationally supported, with higher metallicity and less alpha-element enhanced than the old ones. These results are consistent with the current observational status of bulges, and provide an explanation for some apparently paradoxical observations, such as bulge rejuvenation and metal-content gradients observed. Our results suggest that bulges of L {sub *} galaxies will generically have two bulge populations that can be likened to classical and pseudo-bulges, with differences being in the relative proportions of the two, which may vary due to galaxy mass and specific mass accretion and merger histories.
A TWO-PHASE SCENARIO FOR BULGE ASSEMBLY IN ΛCDM COSMOLOGIES
International Nuclear Information System (INIS)
We analyze and compare the bulges of a sample of L * spiral galaxies in hydrodynamical simulations in a cosmological context, using two different codes, P-DEVA and GASOLINE. The codes regulate star formation in very different ways, with P-DEVA simulations inputting low star formation efficiency under the assumption that feedback occurs on subgrid scales, while the GASOLINE simulations have feedback that drives large-scale outflows. In all cases, the marked knee shape in mass aggregation tracks, corresponding to the transition from an early phase of rapid mass assembly to a later slower one, separates the properties of two populations within the simulated bulges. The bulges analyzed show an important early starburst resulting from the collapse-like fast phase of mass assembly, followed by a second phase with lower star formation, driven by a variety of processes such as disk instabilities and/or mergers. Classifying bulge stellar particles identified at z = 0 into old and young according to these two phases, we found bulge stellar sub-populations with distinct kinematics, shapes, stellar ages, and metal contents. The young components are more oblate, generally smaller, more rotationally supported, with higher metallicity and less alpha-element enhanced than the old ones. These results are consistent with the current observational status of bulges, and provide an explanation for some apparently paradoxical observations, such as bulge rejuvenation and metal-content gradients observed. Our results suggest that bulges of L * galaxies will generically have two bulge populations that can be likened to classical and pseudo-bulges, with differences being in the relative proportions of the two, which may vary due to galaxy mass and specific mass accretion and merger histories.
Milgrom, Mordehai
2016-01-01
Keller and Wadsley (2016) have smugly suggested, recently, that the end of MOND may be in view. This is based on their claim that their highly-restricted sample of $\\Lambda$CDM-simulated galaxies are "consistent" with the observed MOND mass-discrepancy-acceleration relation (MDAR), in particular, with its recent update by McGaugh et al. (2016), based on the SPARC sample. From this they extrapolate to "$\\Lambda$CDM is fully consistent" with the MDAR. I explain why these simulated galaxies do not show that $\\Lambda$CDM accounts for the MDAR. a. Their sample of simulated galaxies contains only 18 high-mass galaxies, within a narrow range of one order of magnitude in baryonic mass, at the very high end of the observed, SPARC sample, which spans 4.5 orders of magnitude in mass. More importantly, the simulated sample has none of the low-mass, low-acceleration galaxies -- abundant in SPARC -- which encapsulate the crux and the nontrivial aspects of the predicted and observed MDAR. The low-acceleration part of the si...
Sanders, R. H.
2005-01-01
I review various ideas on MOND cosmology and structure formation beginning with non-relativistic models in analogy with Newtonian cosmology. I discuss relativistic MOND cosmology in the context of Bekenstein's theory and propose an alternative biscalar effective theory of MOND in which the acceleration parameter is identified with the cosmic time derivative of a matter coupling scalar field. Cosmic CDM appears in this theory as scalar field oscillations of the auxiliary "coupling strength" fi...
DISCOVERY OF A SUPERCLUSTER AT z ∼ 0.91 AND TESTING THE ΛCDM COSMOLOGICAL MODEL
Energy Technology Data Exchange (ETDEWEB)
Kim, Jae-Woo; Im, Myungshin; Lee, Seong-Kook; Hyun, Minhee; Kim, Dohyeong; Choi, Changsu; Hong, Jueun; Kim, Yongjung; Taak, Yoon Chan; Yoon, Yongmin [Center for the Exploration of the Origin of the universe, Department of Physics and Astronomy, Seoul National University, Seoul 151-742 (Korea, Republic of); Edge, Alastair C. [Department of Physics, University of Durham, South Road, Durham DH1 3LE (United Kingdom); Jeon, Yiseul; Jun, Hyunsung David; Karouzos, Marios; Kim, Duho [Astronomy Program, FPRD, Department of Physics and Astronomy, Seoul National University, Seoul 151-742 (Korea, Republic of); Kim, Ji Hoon [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, HI 96720 (United States); Park, Won-Kee, E-mail: kjw0704@gmail.com, E-mail: mim@astro.snu.ac.kr [Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of)
2016-04-10
The ΛCDM cosmological model successfully reproduces many aspects of the galaxy and structure formation of the universe. However, the growth of large-scale structures (LSSs) in the early universe is not well tested yet with observational data. Here, we have utilized wide and deep optical–near-infrared data in order to search for distant galaxy clusters and superclusters (0.8 < z < 1.2). From the spectroscopic observation with the Inamori Magellan Areal Camera and Spectrograph (IMACS) on the Magellan telescope, three massive clusters at z ∼ 0.91 are confirmed in the SSA22 field. Interestingly, all of them have similar redshifts within Δ z ∼ 0.01 with velocity dispersions ranging from 470 to 1300 km s{sup −1}. Moreover, as the maximum separation is ∼15 Mpc, they compose a supercluster at z ∼ 0.91, meaning that this is one of the most massive superclusters at this redshift to date. The galaxy density map implies that the confirmed clusters are embedded in a larger structure stretching over ∼100 Mpc. ΛCDM models predict about one supercluster like this in our surveyed volume, consistent with our finding so far. However, there are more supercluster candidates in this field, suggesting that additional studies are required to determine if the ΛCDM cosmological model can successfully reproduce the LSSs at high redshift.
Wetzel, Andrew R.; Hopkins, Philip F.; Kim, Ji-hoon; Faucher-Giguère, Claude-André; Kereš, Dušan; Quataert, Eliot
2016-08-01
Low-mass “dwarf” galaxies represent the most significant challenges to the cold dark matter (CDM) model of cosmological structure formation. Because these faint galaxies are (best) observed within the Local Group (LG) of the Milky Way (MW) and Andromeda (M31), understanding their formation in such an environment is critical. We present first results from the Latte Project: the Milky Way on Feedback in Realistic Environments (FIRE). This simulation models the formation of an MW-mass galaxy to z=0 within ΛCDM cosmology, including dark matter, gas, and stars at unprecedented resolution: baryon particle mass of 7070 {M}⊙ with gas kernel/softening that adapts down to 1 {pc} (with a median of 25{--}60 {pc} at z=0). Latte was simulated using the GIZMO code with a mesh-free method for accurate hydrodynamics and the FIRE-2 model for star formation and explicit feedback within a multi-phase interstellar medium. For the first time, Latte self-consistently resolves the spatial scales corresponding to half-light radii of dwarf galaxies that form around an MW-mass host down to {M}{star}≳ {10}5 {M}⊙ . Latte’s population of dwarf galaxies agrees with the LG across a broad range of properties: (1) distributions of stellar masses and stellar velocity dispersions (dynamical masses), including their joint relation; (2) the mass-metallicity relation; and (3) diverse range of star formation histories, including their mass dependence. Thus, Latte produces a realistic population of dwarf galaxies at {M}{star}≳ {10}5 {M}⊙ that does not suffer from the “missing satellites” or “too big to fail” problems of small-scale structure formation. We conclude that baryonic physics can reconcile observed dwarf galaxies with standard ΛCDM cosmology.
Cosmic acceleration as the solution to the cosmological constant problem
Mannheim, P D
1999-01-01
In this paper we provide both a diagnosis and resolution of the cosmological constant problem, one in which a large (as opposed to a small) cosmological constant $\\Lambda$ can be made compatible with observation. We trace the origin of the cosmological constant problem to the assumption that Newton's constant $G$ sets the scale for cosmology. And then we show that once this assumption is relaxed (so that the local $G$ as measured in a local Cavendish experiment is no longer to be associated with global cosmology), the very same cosmic acceleration which has served to make the cosmological constant problem so very severe instead then serves to provide us with its potential resolution. In addition, we present an alternate cosmology, one based on conformal gravity (a theory which explicitly possesses no fundamental $G$), and show that once given only that there is to be cosmic acceleration in the conformal theory (i.e. once given only that in the theory the sign of $\\Lambda$ is to specifically be the negative on...
Accelerating Universe without Bigbang singularity in Kalb-Ramond Cosmology
Sen-Gupta, S; Gupta, Soumitra Sen; Sur, Saurabh
2003-01-01
Existence of Bigbang singularity is considered to be the most serious drawback in the standard FRW cosmology. Furthermore to explain the accelerating phase of the Universe (recently detected experimentally) in such a model one needs to include a non-vanishing cosmological constant in the theory by hand. In this note we show that a string originated torsion in the background spacetime provides natural solutions to both these problems. The Universe evolving in a torsioned spacetime is not only free of Bigbang singularity but also exhibits acceleration during it's evolution. The role of dilaton in this context is briefly discussed.
Precision cosmology defeats void models for acceleration
International Nuclear Information System (INIS)
The suggestion that we occupy a privileged position near the center of a large, nonlinear, and nearly spherical void has recently attracted much attention as an alternative to dark energy. Putting aside the philosophical problems with this scenario, we perform the most complete and up-to-date comparison with cosmological data. We use supernovae and the full cosmic microwave background spectrum as the basis of our analysis. We also include constraints from radial baryonic acoustic oscillations, the local Hubble rate, age, big bang nucleosynthesis, the Compton y distortion, and for the first time include the local amplitude of matter fluctuations, σ8. These all paint a consistent picture in which voids are in severe tension with the data. In particular, void models predict a very low local Hubble rate, suffer from an ''old age problem,'' and predict much less local structure than is observed.
Accelerating cosmologies and a phase transition in M-theory
Energy Technology Data Exchange (ETDEWEB)
Wohlfarth, Mattias N.R
2003-06-19
M-theory compactifies on a seven-dimensional time-dependent hyperbolic or flat space to a four-dimensional FLRW cosmology undergoing a period of accelerated expansion in Einstein conformal frame. The strong energy condition is violated by the scalar fields produced in the compactification, as is necessary to evade the no-go theorem for time-independent compactifications. The four-form field strength of eleven-dimensional supergravity smoothly switches on during the period of accelerated expansion in hyperbolic compactifications, whereas in flat compactifications, the three-form potential smoothly changes its sign. For small acceleration times, this behaviour is like a phase transition of the three-form potential, during which the cosmological scale factor approximately doubles.
Accelerating Cosmologies and a Phase Transition in M-Theory
Wohlfarth, M N R
2003-01-01
M-theory compactifies on a seven-dimensional time-dependent hyperbolic or flat space to a four-dimensional FLRW cosmology undergoing a period of accelerated expansion in Einstein conformal frame. The strong energy condition is violated by the scalar fields produced in the compactification, as is necessary to evade the no-go theorem for time-independent compactifications. The four-form field strength of eleven-dimensional supergravity smoothly switches on during the period of accelerated expansion in hyperbolic compactifications, whereas in flat compactifications, the three-form potential smoothly changes its sign. For small acceleration times, this behaviour is like a phase transition of the three-form potential, during which the cosmological scale factor approximately doubles.
Cosmic Rays Accelerated at Cosmological Shock Waves
Indian Academy of Sciences (India)
Renyi Ma; Dongsu Ryu; Hyesung Kang
2011-03-01
Based on hydrodynamic numerical simulations and diffusive shock acceleration model, we calculated the ratio of cosmic ray (CR) to thermal energy. We found that the CR fraction can be less than ∼ 0.1 in the intracluster medium, while it would be of order unity in the warm-hot intergalactic medium.
Redshift remapping and cosmic acceleration in dark-matter-dominated cosmological models
Wojtak, Radosław
2016-01-01
The standard relation between the cosmological redshift and cosmic scale factor underlies cosmological inference from virtually all kinds of cosmological observations, leading to the emergence of the LambdaCDM cosmological model. This relation is not a fundamental theory and thus observational determination of this function (redshift remapping) should be regarded as an insightful alternative to holding its standard form in analyses of cosmological data. Here we present non-parametric reconstructions of redshift remapping in dark-matter-dominated models and constraints on cosmological parameters from a joint analysis of all primary cosmological probes including the local measurement of the Hubble constant, Type Ia supernovae, baryonic acoustic oscillations (BAO), Planck observations of the cosmic microwave background (CMB) radiation (temperature power spectrum) and cosmic chronometers. The reconstructed redshift remapping points to an additional boost of redshift operating in late epoch of cosmic evolution, bu...
Area metric gravity and accelerating cosmology
Punzi, R; Wohlfarth, M N R; Punzi, Raffaele; Schuller, Frederic P.; Wohlfarth, Mattias N.R.
2007-01-01
Area metric manifolds emerge as effective classical backgrounds in quantum string theory and quantum gauge theory, and present a true generalization of metric geometry. Here, we consider area metric manifolds in their own right, and develop in detail the foundations of area metric differential geometry. Based on the construction of an area metric curvature scalar, which reduces in the metric-induced case to the Ricci scalar, we re-interpret the Einstein-Hilbert action as dynamics for an area metric spacetime. In contrast to modifications of general relativity based on metric geometry, no continuous deformation scale needs to be introduced; the extension to area geometry is purely structural and thus rigid. We present an intriguing prediction of area metric gravity: without dark energy or fine-tuning, the late universe exhibits a small acceleration.
The Mass-Discrepancy Acceleration Relation: a Natural Outcome of Galaxy Formation in CDM halos
Ludlow, Aaron D; Schaller, Matthieu; Theuns, Tom; Frenk, Carlos S; Bower, Richard; Schaye, Joop; Crain, Robert A; Navarro, Julio F; Fattahi, Azadeh; Oman, Kyle A
2016-01-01
We analyze the total and baryonic acceleration profiles of a set of well-resolved galaxies identified in the EAGLE suite of hydrodynamic simulations. Our runs start from the same initial conditions but adopt different subgrid models for stellar and AGN feedback, resulting in diverse populations of galaxies by the present day. Some of them reproduce observed galaxy scaling relations, while others do not. However, regardless of the feedback implementation, all of our galaxies follow closely a simple relationship between the total and baryonic acceleration profiles, consistent with recent observations of rotationally supported galaxies. The relation has small scatter: different feedback processes -- which produce different galaxy populations -- mainly shift galaxies along the relation, rather than perpendicular to it. Furthermore, galaxies exhibit a single characteristic acceleration, $g_{\\dagger}$, above which baryons dominate the mass budget, as observed. These observations have been hailed as evidence for mod...
Rotating and accelerating black holes with cosmological constant
Chen, Yu; Ng, Cheryl; Teo, Edward
2016-01-01
We propose a new form of the rotating C-metric with cosmological constant, which generalises the form found by Hong and Teo for the Ricci-flat case. This solution describes the entire class of spherical black holes undergoing rotation and acceleration in dS or AdS space-time. The new form allows us to identify the complete ranges of coordinates and parameters of this solution. We perform a systematic study of its geometrical and physical properties, and of the various limiting cases that aris...
Magg, Mattis; Hartwig, Tilman; Glover, Simon C. O.; Klessen, Ralf S.; Whalen, Daniel J.
2016-11-01
With new observational facilities becoming available soon, discovering and characterizing supernovae from the first stars will open up alternative observational windows to the end of the cosmic dark ages. Based on a semi-analytical merger tree model of early star formation, we constrain Population III supernova rates. We find that our method reproduces the Population III supernova rates of large-scale cosmological simulations very well. Our computationally efficient model allows us to survey a large parameter space and to explore a wide range of different scenarios for Population III star formation. Our calculations show that observations of the first supernovae can be used to differentiate between cold and warm dark matter models and to constrain the corresponding particle mass of the latter. Our predictions can also be used to optimize survey strategies with the goal to maximize supernova detection rates.
Magg, Mattis; Glover, Simon C O; Klessen, Ralf S; Whalen, Daniel J
2016-01-01
With new observational facilities becoming available soon, discovering and characterising supernovae from the first stars will open up alternative observational windows to the end of the cosmic dark ages. Based on a semi-analytical merger tree model of early star formation we constrain Population III supernova rates. We find that our method reproduces the Population III supernova rates of large-scale cosmological simulations very well. Our computationally efficient model allows us to survey a large parameter space and to explore a wide range of different scenarios for Population III star formation. Our calculations show that observations of the first supernovae can be used to differentiate between cold and warm dark matter models and to constrain the corresponding particle mass of the latter. Our predictions can also be used to optimize survey strategies with the goal to maximize supernova detection rates.
Akarsu, Ozgur
2013-01-01
A class of cosmological solutions of higher dimensional Einstein field equations with the energy-momentum tensor of a homogeneous, isotropic fluid as the source are considered with an anisotropic metric that includes the direct sum of a 3-dimensional (physical, flat) external space metric and an n-dimensional (compact, flat) internal space metric. A simple kinematical constraint is postulated that correlates the expansion rates of the external and internal spaces in terms of a real parameter \\lambda. A specific solution for which both the external and internal spaces expand at different rates is given analytically for n=3. Assuming that the internal dimensions were at Planck length scales at the beginning t=0, the external space starts with a Big Bang and the external and internal spaces both reach the same size after 10^{-176} Gyr. Then during the lifetime of the observed universe (13.7 Gyr), the external dimensions would expand 10^{59} times while the internal dimensions expand only 1.49 times. The effectiv...
Halting eternal acceleration with an effective negative cosmological constant
Cardone, Vincenzo F; Nodal, Yoelsy Leiva
2008-01-01
In order to solve the problem of eternal acceleration, a model has been recently proposed including both a negative cosmological constant $\\Lambda$ and a scalar field evolving under the action of an exponential potential. We further explore this model by contrasting it against the Hubble diagram of Type Ia supernovae, the gas mass fraction in galaxy clusters and the acoustic peak and shift parameters. It turns out that the model is able to fit quite well this large dataset so that we conclude that a negative $\\Lambda$ is indeed allowed and could represent a viable mechanism to halt eternal acceleration. In order to avoid problems with theoretical motivations for both a negative $\\Lambda$ term and the scalar field, we reconstruct the gravity Lagrangian $f(R)$ of a fourth order theory of gravity predicting the same dynamics (scale factor and Hubble parameter) as the starting model. We thus end up with a $f(R)$ theory able to both fit the data and solve the problem of eternal acceleration without the need of unu...
The velocity field in MOND cosmology
Candlish, G N
2016-01-01
The recently developed code for N-body/hydrodynamics simulations in Modified Newtonian Dynamics (MOND), known as RAyMOND, is used to investigate the consequences of MOND on structure formation in a cosmological context, with a particular focus on the velocity field. This preliminary study investigates the results obtained with the two formulations of MOND implemented in RAyMOND, as well as considering the effects of changing the choice of MOND interpolation function, and the cosmological evolution of the MOND acceleration scale. The simulations are contrived such that structure forms in a background cosmology that is similar to $\\Lambda$CDM, but with a significantly lower matter content. Given this, and the fact that a fully consistent MOND cosmology is still lacking, we compare our results with a standard $\\Lambda$CDM simulation, rather than observations. As well as demonstrating the effectiveness of using RAyMOND for cosmological simulations, it is shown that a significant enhancement of the velocity field ...
Deformed phase space Kaluza-Klein cosmology and late time acceleration
Sabido, M.; Yee-Romero, C.
2016-06-01
The effects of phase space deformations on Kaluza-Klein cosmology are studied. The deformation is introduced by modifying the symplectic structure of the minisuperspace variables. In the deformed model, we find an accelerating scale factor and therefore infer the existence of an effective cosmological constant from the phase space deformation parameter β.
Cosmology in an accelerated universe: observations and phenomenology
Sendra Server, Irene
2014-01-01
En las últimas décadas la cosmología ha experimentado notables avances como consecuencia del desarrollo de nuevos experimentos que nos han abastecido con precisos datos observacionales. La calidad de estos datos ha permitido construir una imagen global del universo actual; un universo acelerado compuesto principalmente por materia oscura (23%) distinta a la materia ordinaria (5%), y energía oscura (70%), la componente del universo que contrarresta el efecto gravitatorio y explica la expansión...
Statistical Inference in Cosmology
Sellentin, Elena
2016-01-01
Analysis of cosmic data is the only way to determine whether General Relativity is the law of gravity also on the largest scales in our Universe. The current standard model of cosmology, ΛCDM, is based on General Relativity, and fits all currently available data flawlessly. However, theoretical dissatisfaction with ΛCDM exists: cosmological data probe gravitational interactions, and ΛCDM fits the data only because it introduces two components of startling gravitional behavio...
Comment on "Accelerating cosmological expansion from shear and bulk viscosity"
Giovannini, Massimo
2015-01-01
In a recent Letter [Phys. Rev. Lett. 114 091301 (2105)] the cause of the acceleration of the present Universe has been identified with the shear viscosity of an imperfect relativistic fluid even in the absence of any bulk viscous contribution. The gist of this comment is that the shear viscosity, if anything, can only lead to an accelerated expansion over sufficiently small scales well inside the Hubble radius.
International Nuclear Information System (INIS)
An extensive first part on a wealth of observational results relevant to cosmology lays the foundation for the second and central part of the book; the chapters on general relativity, the various cosmological theories, and the early universe. The authors present in a complete and almost non-mathematical way the ideas and theoretical concepts of modern cosmology including the exciting impact of high-energy particle physics, e.g. in the concept of the ''inflationary universe''. The final part addresses the deeper implications of cosmology, the arrow of time, the universality of physical laws, inflation and causality, and the anthropic principle
Rubakov, V A
2014-01-01
In these lectures we first concentrate on the cosmological problems which, hopefully, have to do with the new physics to be probed at the LHC: the nature and origin of dark matter and generation of matter-antimatter asymmetry. We give several examples showing the LHC cosmological potential. These are WIMPs as cold dark matter, gravitinos as warm dark matter, and electroweak baryogenesis as a mechanism for generating matter-antimatter asymmetry. In the remaining part of the lectures we discuss the cosmological perturbations as a tool for studying the epoch preceeding the conventional hot stage of the cosmological evolution.
Can f(T) gravity theories mimic ΛCDM cosmic history
Energy Technology Data Exchange (ETDEWEB)
Setare, M.R.; Mohammadipour, N., E-mail: rezakord@ipm.ir, E-mail: N.Mohammadipour@uok.ac.ir [Department of Science, University of Kurdistan, Sanandaj (Iran, Islamic Republic of)
2013-01-01
Recently the teleparallel Lagrangian density described by the torsion scalar T has been extended to a function of T. The f(T) modified teleparallel gravity has been proposed as the natural gravitational alternative for dark energy to explain the late time acceleration of the universe. In order to reconstruct the function f(T) by demanding a background ΛCDM cosmology we assume that, (i) the background cosmic history provided by the flat ΛCDM (the radiation ere with ω{sub eff} = (1/3), matter and de Sitter eras with ω{sub eff} = 0 and ω{sub eff} = −1, respectively) (ii) the radiation dominate in the radiation era with Ω{sub 0r} = 1 and the matter dominate during the matter phases when Ω{sub 0m} = 1. We find the cosmological dynamical system which can obey the ΛCDM cosmic history. In each era, we find a critical lines that, the radiation dominated and the matter dominated are one points of them in the radiation and matter phases, respectively. Also, we drive the cosmologically viability condition for these models. We investigate the stability condition with respect to the homogeneous scalar perturbations in each era and we obtain the stability conditions for the fixed points in each eras. Finally, we reconstruct the function f(T) which mimics cosmic expansion history.
Scalar Speed Limits and Cosmology: Acceleration from D-cceleration
Silverstein, E; Silverstein, Eva; Tong, David
2003-01-01
Causality on the gravity side of the AdS/CFT correspondence restricts motion on the moduli space of the N=4 super Yang Mills theory by imposing a speed limit on how fast the scalar field may roll. This effect can be traced to higher derivative operators arising from integrating out light degrees of freedom near the origin. In the strong coupling limit of the theory, the dynamics is well approximated by the Dirac-Born-Infeld Lagrangian for a probe D3-brane moving toward the horizon of the AdS Poincare patch, combined with an estimate of the (ultimately suppressed) rate of particle and string production in the system. We analyze the motion of a rolling scalar field explicitly in the strong coupling regime of the field theory, and extend the analysis to cosmological systems obtained by coupling this type of field theory to four dimensional gravity. This leads to a mechanism for slow roll inflation for a massive scalar at subPlanckian VEV without need for a flat potential (realizing a version of k-inflation in a ...
Dark Energy or local acceleration?
Feoli, Antonio
2016-01-01
We find that an observer with a suitable acceleration relative to the frame comoving whit the cosmic fluid, in the context of the FRW decelerating universe, measures the same cosmological redshift as the LambdaCDM model. The estimated value of this acceleration is beta = 1.4x10^-9m/s^2. The problem of a too high peculiar velocity can be solved assuming, for the observer, a sort of helical motion.
Gauss-Bonnet Cosmology Unifying Late and Early-time Acceleration Eras with Intermediate Eras
Oikonomou, V K
2016-01-01
In this paper we demonstrate that with vacuum $F(G)$ gravity it is possible to describe the unification of late and early-time acceleration eras with the radiation and matter domination era. The Hubble rate of the unified evolution contains two mild singularities, so called Type IV singularities, and the evolution itself has some appealing features, such as the existence of a deceleration-acceleration transition at late times. We also address quantitatively a fundamental question related to modified gravity models description of cosmological evolution: Is it possible for all modified gravity descriptions of our Universe evolution, to produce a nearly scale invariant spectrum of primordial curvature perturbations? As we demonstrate, the answer for the $F(G)$ description is no, since the resulting power spectrum is not scale invariant, in contrast to the $F(R)$ description studied in the literature. Therefore, although the cosmological evolution can be realized in the context of vacuum $F(G)$ gravity, the evolu...
Acceleration-enlarged symmetries in nonrelativistic space-time with a cosmological constant
Energy Technology Data Exchange (ETDEWEB)
Lukierski, J. [University of Wroclaw, Institute for Theoretical Physics, Wroclaw (Poland); University of Valencia, Department of Theoretical Physics, Burjassot (Valencia) (Spain); Zakrzewski, W.J. [University of Durham, Department of Mathematical Sciences, Durham (United Kingdom); Stichel, P.C.
2008-05-15
By considering the nonrelativistic limit of de Sitter geometry one obtains the nonrelativistic space-time with a cosmological constant and Newton-Hooke (NH) symmetries. We show that the NH symmetry algebra can be enlarged by the addition of the constant acceleration generators and endowed with central extensions (one in any dimension (D) and three in D=(2+1)). We present a classical Lagrangian and Hamiltonian framework for constructing models quasi-invariant under enlarged NH symmetries that depend on three parameters described by three nonvanishing central charges. The Hamiltonian dynamics then splits into external and internal sectors with new noncommutative structures of external and internal phase spaces. We show that in the limit of vanishing cosmological constant the system reduces to the one, which possesses acceleration-enlarged Galilean symmetries. (orig.)
Acceleration-Enlarged Symmetries in Nonrelativistic Space-Time with a Cosmological Constant
Lukierski, J.; Stichel, P. C.; Zakrzewski, W. J.
2007-01-01
By considering the nonrelativistic limit of de-Sitter geometry one obtains the nonrelativistic space-time with a cosmological constant and Newton-Hooke (NH) symmetries. We show that the NH symmetry algebra can be enlarged by the addition of the constant acceleration generators and endowed with central extensions (one in any dimension (D) and three in D=(2+1)). We present a classical Lagrangian and Hamiltonian framework for constructing models quasi-invariant under enlarged NH symmetries which...
Running vacuum versus the $\\Lambda$CDM
Gómez-Valent, Adrià; Pérez, Javier de Cruz
2016-01-01
It is well-known that a constant $\\Lambda$-term is a traditional building block of the concordance $\\Lambda$CDM model. We show that this assumption is not necessarily the optimal one from the phenomenological point of view. The class of running vacuum models, with a possible running of the gravitational coupling G, are capable to fit the overall cosmological data SNIa+BAO+H(z)+LSS+BBN+CMB better than the $\\Lambda$CDM, namely at a level of $\\sim 3\\sigma$ and with Akaike and Bayesian information criteria supporting a strong level of statistical evidence on this fact. Here we report on the results of such analysis.
Demianski, Marek; Sawant, Disha; Amati, Lorenzo
2016-01-01
Context. Explaining the accelerated expansion of the Universe is one of the fundamental challenges in physics today. Cosmography provides information about the evolution of the universe derived from measured distances, assuming only that the space time ge- ometry is described by the Friedman-Lemaitre-Robertson-Walker metric, and adopting an approach that effectively uses only Taylor expansions of basic observables. Aims. We perform a high-redshift analysis to constrain the cosmographic expansion up to the fifth order. It is based on the Union2 type Ia supernovae data set, the gamma-ray burst Hubble diagram, a data set of 28 independent measurements of the Hubble param- eter, baryon acoustic oscillations measurements from galaxy clustering and the Lyman-{\\alpha} forest in the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), and some Gaussian priors on h and {\\Omega}M . Methods. We performed a statistical analysis and explored the probability distributions of the cosmographic parameters. By building up ...
Self-accelerating cosmologies and hairy black holes in ghost-free bigravity and massive gravity
International Nuclear Information System (INIS)
We present a survey of the known cosmological and black hole solutions in ghost-free bigravity and massive gravity theories. These can be divided into three classes. First, there are solutions with proportional metrics, which are the same as in General Relativity with a cosmological term, which can be positive, negative or zero. Secondly, for spherically symmetric systems, there are solutions with non-bidiagonal metrics. The g-metric fulfils Einstein equations with a positive cosmological term and a matter source, while the f-metric is anti-de Sitter. The third class contains solutions with bidiagonal metrics, and these can be quite complex. The time-dependent solutions describe homogeneous (isotropic or anisotropic) cosmologies which show a late-time self-acceleration or other types of behavior. The static solutions describe black holes with a massive graviton hair, and also globally regular lumps of energy. None of these are asymptotically flat. Including a matter source gives rise to asymptotically flat solutions which exhibit the Vainshtein mechanism of recovery of General Relativity in a finite region. (paper)
CDM Country Guide for Cambodia
International Nuclear Information System (INIS)
Under the Integrated Capacity Strengthening for the CDM (ICS-CDM) programme, IGES presents the CDM Country Guides, a series of manuals on CDM project development for Cambodia, China, India, Indonesia, the Philippines, and Thailand. These guidebooks aim at facilitating CDM project developments in Asia by providing essential information to both project developers and potential investors. This volume is on Cambodia
Livio, Mario
2000-12-01
Advance Praise for The Accelerating Universe "The Accelerating Universe is not only an informative book about modern cosmology. It is rich storytelling and, above all, a celebration of the human mind in its quest for beauty in all things." -Alan Lightman, author of Einstein's Dreams "This is a wonderfully lucid account of the extraordinary discoveries that have made the last years a golden period for observational cosmology. But Mario Livio has not only given the reader one clear explanation after another of what astronomers are up to, he has used them to construct a provocative argument for the importance of aesthetics in the development of science and for the inseparability of science, art, and culture." -Lee Smolin, author of The Life of the Cosmos "What a pleasure to read! An exciting, simple account of the universe revealed by modern astronomy. Beautifully written, clearly presented, informed by scientific and philosophical insights." -John Bahcall, Institute for Advanced Study "A book with charm, beauty, elegance, and importance. As authoritative a journey as can be taken through modern cosmology." -Allan Sandage, Observatories of the Carnegie Institution of Washington
Gauss-Bonnet cosmology unifying late and early-time acceleration eras with intermediate eras
Oikonomou, V. K.
2016-07-01
In this paper we demonstrate that with vacuum F(G) gravity it is possible to describe the unification of late and early-time acceleration eras with the radiation and matter domination era. The Hubble rate of the unified evolution contains two mild singularities, so called Type IV singularities, and the evolution itself has some appealing features, such as the existence of a deceleration-acceleration transition at late times. We also address quantitatively a fundamental question related to modified gravity models description of cosmological evolution: Is it possible for all modified gravity descriptions of our Universe evolution, to produce a nearly scale invariant spectrum of primordial curvature perturbations? As we demonstrate, the answer for the F(G) description is no, since the resulting power spectrum is not scale invariant, in contrast to the F(R) description studied in the literature. Therefore, although the cosmological evolution can be realized in the context of vacuum F(G) gravity, the evolution is not compatible with the observational data, in contrast to the F(R) gravity description of the same cosmological evolution.
Acceleration-Enlarged Symmetries in Nonrelativistic Space-Time with a Cosmological Constant
Lukierski, J; Zakrzewski, W J
2007-01-01
By considering the nonrelativistic limit of de-Sitter geometry one obtains the nonrelativistic space-time with a cosmological constant and Newton-Hooke (NH) symmetries. We show that the NH symmetry algebra can be enlarged by the addition of the constant acceleration generators and endowed with central extensions (one in any dimension (D) and three in D=(2+1)). We present a classical Lagrangian and Hamiltonian framework for constructing models quasi-invariant under enlarged NH symmetries which depend on three parameters described by three nonvanishing central charges. The Hamiltonian dynamics then splits into external and internal sectors with new non-commutative structures of external and internal phase spaces. We show that in the limit of vanishing cosmological constant the system reduces to the one presented in [1] which possesses accelaration-enlarged Galilean symmetries.
International Nuclear Information System (INIS)
I review the intrinsic properties of neutrinos as deduced from cosmological, astrophysical, and laboratory experiments. Bounds on magnetic moments and theoretical models which yield large moments but small masses are briefly discussed. The MSW solution to the solar neutrino problem is reviewed in light of the existing data from the 37Cl and Kamiokande II experiments. The combined data disfavor the adiabatic solution and tend to support either the large angle solution or the nonadiabatic one. In the former case the 71Ga signal will be suppressed by the same factor as for 37Cl, and in the latter case the suppression factor could be as large as 10 or more. 41 refs
International Nuclear Information System (INIS)
Under the Integrated Capacity Strengthening for the Clean Development Mechanism (ICS-CDM) programme, IGES presents the CDM Country Guides, a series of manuals on CDM project development for Cambodia, China, India, Indonesia, the Philippines, and Thailand. These guidebooks aim at facilitating CDM project developments in Asia by providing essential information to both project developers and potential investors. Chapter 1, Introduction, is a summary of issues that developers and investors in CDM projects should be aware of. Includes tips for readers to effectively use the guidebook to find specific information. Chapter 2, Country Profile, comprises a profile that provides a broad picture of the country, including social, economic, and political information, as well as an overview of the country's energy situation, which is important for project development and investment. Chapter 3, The CDM Project Cycle, gives an explanation of the general CDM project cycle, which includes identifying a project, issuance of carbon credits, requirements, and stakeholders for each process. Chapter 4, Possible CDM Projects in the Country, is an overview of the country's potential resources and sectoral or project type categories that hold potential for CDM projects. Chapter 5, Government Authorities, gives a comprehensive picture of the CDM-related institutional framework and its inter-organisational relationships. Chapter 6, CDM Project Approval Procedures and Requirements Steps, informs about obtaining project approval and its requirements (e.g., country-specific provisions on additionality, sustainable development criteria, and environmental impact assessment) in the host country. Chapter 7, Laws and Regulations, is an overview of basic investment-related laws, environmental and property law, and sector-specific regulations relevant to CDM project activities. Chapter 8, Fiscal and Financing Issues, gives practical information on the financial market in the host country (both
Energy Technology Data Exchange (ETDEWEB)
NONE
2005-07-01
Under the Integrated Capacity Strengthening for the Clean Development Mechanism (ICS-CDM) programme, IGES presents the CDM Country Guides, a series of manuals on CDM project development for Cambodia, China, India, Indonesia, the Philippines, and Thailand. These guidebooks aim at facilitating CDM project developments in Asia by providing essential information to both project developers and potential investors. Chapter 1, Introduction, is a summary of issues that developers and investors in CDM projects should be aware of. Includes tips for readers to effectively use the guidebook to find specific information. Chapter 2, Country Profile, comprises a profile that provides a broad picture of the country, including social, economic, and political information, as well as an overview of the country's energy situation, which is important for project development and investment. Chapter 3, The CDM Project Cycle, gives an explanation of the general CDM project cycle, which includes identifying a project, issuance of carbon credits, requirements, and stakeholders for each process. Chapter 4, Possible CDM Projects in the Country, is an overview of the country's potential resources and sectoral or project type categories that hold potential for CDM projects. Chapter 5, Government Authorities, gives a comprehensive picture of the CDM-related institutional framework and its inter-organisational relationships. Chapter 6, CDM Project Approval Procedures and Requirements Steps, informs about obtaining project approval and its requirements (e.g., country-specific provisions on additionality, sustainable development criteria, and environmental impact assessment) in the host country. Chapter 7, Laws and Regulations, is an overview of basic investment-related laws, environmental and property law, and sector-specific regulations relevant to CDM project activities. Chapter 8, Fiscal and Financing Issues, gives practical information on the financial market in the host country
Future evolution of bound superclusters in an accelerating Universe
Araya-Melo, Pablo A.; Reisenegger, Andreas; Meza, Andres; van de Weygaert, Rien; Duenner, Rolando; Quintana, Hernan
2009-01-01
The evolution of marginally bound supercluster-like objects in all accelerating Lambda cold dark matter (Lambda CDM) Universe is followed, by means of cosmological simulations, from the present time to all expansion factor a = 100. The objects are identified on the basis of the binding density crite
Moffat, J W
2016-01-01
An alternative to the postulate of dark energy required to explain the accelerated expansion of the universe is to adopt an inhomogeneous cosmological model to explain the supernovae data without dark energy. We adopt a void cosmology model, based on the inhomogeneous Lema\\^{i}tre-Tolman-Bondi solution of Einstein's field equations. The model can resolve observational anomalies in the $\\Lambda CDM$ model, such as the discrepancy between the locally measured value of the Hubble constant, $H_0=73.24\\pm 1.74\\,{\\rm km}\\,{\\rm s}^{-1}\\,{\\rm Mpc}^{-1}$, and the $H_0=66.93\\pm 0.62\\,{\\rm km}\\,{\\rm s}^{-1}\\,{\\rm Mpc}^{-1}$ determined by the Planck satellite data and the $\\Lambda CDM$ model, and the lithium $^{7}{\\rm Li}$ problem, which is a $5\\sigma$ mismatch between the theoretical prediction for the $^{7}{\\rm Li}$ from big bang nucleosynthesis and the value that we observe locally today at $z=0$. The void model can also resolve the tension between the number of massive clusters derived from the Sunyaev-Zel'dovich eff...
Implications of an absolute simultaneity theory for cosmology and universe acceleration.
Kipreos, Edward T
2014-01-01
An alternate Lorentz transformation, Absolute Lorentz Transformation (ALT), has similar kinematics to special relativity yet maintains absolute simultaneity in the context of a preferred reference frame. In this study, it is shown that ALT is compatible with current experiments to test Lorentz invariance only if the proposed preferred reference frame is locally equivalent to the Earth-centered non-rotating inertial reference frame, with the inference that in an ALT framework, preferred reference frames are associated with centers of gravitational mass. Applying this theoretical framework to cosmological data produces a scenario of universal time contraction in the past. In this scenario, past time contraction would be associated with increased levels of blueshifted light emissions from cosmological objects when viewed from our current perspective. The observation that distant Type Ia supernovae are dimmer than predicted by linear Hubble expansion currently provides the most direct evidence for an accelerating universe. Adjusting for the effects of time contraction on a redshift-distance modulus diagram produces a linear distribution of supernovae over the full redshift spectrum that is consistent with a non-accelerating universe. PMID:25536116
Implications of an absolute simultaneity theory for cosmology and universe acceleration.
Kipreos, Edward T
2014-01-01
An alternate Lorentz transformation, Absolute Lorentz Transformation (ALT), has similar kinematics to special relativity yet maintains absolute simultaneity in the context of a preferred reference frame. In this study, it is shown that ALT is compatible with current experiments to test Lorentz invariance only if the proposed preferred reference frame is locally equivalent to the Earth-centered non-rotating inertial reference frame, with the inference that in an ALT framework, preferred reference frames are associated with centers of gravitational mass. Applying this theoretical framework to cosmological data produces a scenario of universal time contraction in the past. In this scenario, past time contraction would be associated with increased levels of blueshifted light emissions from cosmological objects when viewed from our current perspective. The observation that distant Type Ia supernovae are dimmer than predicted by linear Hubble expansion currently provides the most direct evidence for an accelerating universe. Adjusting for the effects of time contraction on a redshift-distance modulus diagram produces a linear distribution of supernovae over the full redshift spectrum that is consistent with a non-accelerating universe.
Implications of an absolute simultaneity theory for cosmology and universe acceleration.
Directory of Open Access Journals (Sweden)
Edward T Kipreos
Full Text Available An alternate Lorentz transformation, Absolute Lorentz Transformation (ALT, has similar kinematics to special relativity yet maintains absolute simultaneity in the context of a preferred reference frame. In this study, it is shown that ALT is compatible with current experiments to test Lorentz invariance only if the proposed preferred reference frame is locally equivalent to the Earth-centered non-rotating inertial reference frame, with the inference that in an ALT framework, preferred reference frames are associated with centers of gravitational mass. Applying this theoretical framework to cosmological data produces a scenario of universal time contraction in the past. In this scenario, past time contraction would be associated with increased levels of blueshifted light emissions from cosmological objects when viewed from our current perspective. The observation that distant Type Ia supernovae are dimmer than predicted by linear Hubble expansion currently provides the most direct evidence for an accelerating universe. Adjusting for the effects of time contraction on a redshift-distance modulus diagram produces a linear distribution of supernovae over the full redshift spectrum that is consistent with a non-accelerating universe.
Cosmological Implications of Trace-Charged Dark Matter
Morgan, Jason P
2016-01-01
Trace charge imbalances can explain puzzling cosmological observations such as the large `missing' fraction of electrons in cosmic rays and their contrast to the charge-neutral solar wind, the extreme energy sources that sustain quasars, galactic jets, and active galactic nuclei, the origin and nature of `dark matter' galaxy haloes, and the apparent acceleration of the expansion of the Universe, obviating $\\Lambda$CDM. When there are $\\sim \
Cosmological tests of modified gravity.
Koyama, Kazuya
2016-04-01
We review recent progress in the construction of modified gravity models as alternatives to dark energy as well as the development of cosmological tests of gravity. Einstein's theory of general relativity (GR) has been tested accurately within the local universe i.e. the Solar System, but this leaves the possibility open that it is not a good description of gravity at the largest scales in the Universe. This being said, the standard model of cosmology assumes GR on all scales. In 1998, astronomers made the surprising discovery that the expansion of the Universe is accelerating, not slowing down. This late-time acceleration of the Universe has become the most challenging problem in theoretical physics. Within the framework of GR, the acceleration would originate from an unknown dark energy. Alternatively, it could be that there is no dark energy and GR itself is in error on cosmological scales. In this review, we first give an overview of recent developments in modified gravity theories including f(R) gravity, braneworld gravity, Horndeski theory and massive/bigravity theory. We then focus on common properties these models share, such as screening mechanisms they use to evade the stringent Solar System tests. Once armed with a theoretical knowledge of modified gravity models, we move on to discuss how we can test modifications of gravity on cosmological scales. We present tests of gravity using linear cosmological perturbations and review the latest constraints on deviations from the standard [Formula: see text]CDM model. Since screening mechanisms leave distinct signatures in the non-linear structure formation, we also review novel astrophysical tests of gravity using clusters, dwarf galaxies and stars. The last decade has seen a number of new constraints placed on gravity from astrophysical to cosmological scales. Thanks to on-going and future surveys, cosmological tests of gravity will enjoy another, possibly even more, exciting ten years. PMID:27007681
Darabi, F
2009-01-01
We study a $(4+D)$-dimensional Kaluza-Klein cosmology with a Robertson-Walker type metric having two scale factors $a$ and $R$, corresponding to $D$-dimensional internal space and 4-dimensional universe, respectively. By introducing an exotic matter in the form of perfect fluid with an special equation of state, as the space-time part of the higher dimensional energy-momentum tensor, a four dimensional effective decaying cosmological term appears as $\\lambda \\sim R^{-m}$ with $0 \\leq m\\leq 2$, playing the role of an evolving dark energy in the universe. By taking $m=2$, which has some interesting implications in reconciling observations with inflationary models and is consistent with quantum tunneling, the resulting Einstein's field equations yield the exponential solutions for the scale factors $a$ and $R$. These exponential behaviors may account for the dynamical compactification of extra dimensions and the accelerating expansion of the 4-dimensional universe in terms of Hubble parameter, $H$. The accelerat...
The accelerating universe and other cosmological aspects of modified gravity models
de Felice, Antonio
I give a short introduction to standard cosmology and a review of what it is meant by "the dark energy enigma" in chapter l. In chapter 2, I mention and describe some attempts found in the literature of the past few years to attack this problem. Dark energy candidates for which the equation-of-state parameter w is less than -1 violate the dominant energy condition. In scalar-tensor theories of gravity, however, the expansion of the universe can mimic the behavior of general relativity with w the universe in such models, examining the possibilities for cosmic acceleration and other ultimate destinies. The models generically possess de Sitter space as an unstable solution and exhibit an interesting set of attractor solutions which, in some cases, provide alternatives to dark energy models. In chapter 5, I study a baryogenesis mechanism operating in the context of hyperextended inflation and making use of a coupling between the scalar field and a standard model global current, such as B or B - L . The method is efficient at temperatures at which these currents are not conserved due to some higher dimensional operator. The particle physics and cosmological phenomenology are discussed. I consider constraints stemming from nucleosynthesis and solar system experiments.
Hydrodynamical N-body simulations of coupled dark energy cosmologies
Baldi, Marco; Pettorino, Valeria; Robbers, Georg; Springel, Volker
2010-04-01
If the accelerated expansion of the Universe at the present epoch is driven by a dark energy scalar field, there may well be a non-trivial coupling between the dark energy and the cold dark matter (CDM) fluid. Such interactions give rise to new features in cosmological structure growth, like an additional long-range attractive force between CDM particles, or variations of the dark matter particle mass with time. We have implemented these effects in the N-body code GADGET-2 and present results of a series of high-resolution N-body simulations where the dark energy component is directly interacting with the CDM. As a consequence of the new physics, CDM and baryon distributions evolve differently both in the linear and in the non-linear regime of structure formation. Already on large scales, a linear bias develops between these two components, which is further enhanced by the non-linear evolution. We also find, in contrast with previous work, that the density profiles of CDM haloes are less concentrated in coupled dark energy cosmologies compared with ΛCDM, and that this feature does not depend on the initial conditions setup, but is a specific consequence of the extra physics induced by the coupling. Also, the baryon fraction in haloes in the coupled models is significantly reduced below the universal baryon fraction. These features alleviate tensions between observations and the ΛCDM model on small scales. Our methodology is ideally suited to explore the predictions of coupled dark energy models in the fully non-linear regime, which can provide powerful constraints for the viable parameter space of such scenarios.
Miniati, F; Kang, H; Jones, T W; Miniati, Francesco; Ryu, Dongsu; Kang, Hyesung
2001-01-01
We investigate the production of cosmic ray (CR) protons at cosmological shocks by performing, for the first time, numerical simulations of large scale structure formation that include directly the acceleration, transport and energy losses of the high energy particles. CRs are injected at shocks according to the thermal leakage model and, thereafter, accelerated to a power-law distribution as indicated by the test particle limit of the diffusive shock acceleration theory. The evolution of the CR protons accounts for losses due to adiabatic expansion/compression, Coulomb collisions and inelastic p-p scattering. Our results suggest that CR protons produced at shocks formed in association with the process of large scale structure formation could amount to a substantial fraction of the total pressure in the intra-cluster medium. Their presence should be easily revealed by GLAST through detection of gamma-ray flux from the decay of neutral pions produced in inelastic p-p collisions of such CR protons with nuclei o...
Beyond six parameters: Extending Λ CDM
Di Valentino, Eleonora; Melchiorri, Alessandro; Silk, Joseph
2015-12-01
Cosmological constraints are usually derived under the assumption of a six-parameter Λ CDM theoretical framework or simple one-parameter extensions. In this paper we present, for the first time, cosmological constraints in a significantly extended scenario, varying up to 12 cosmological parameters simultaneously, including the sum of neutrino masses, the neutrino effective number, the dark energy equation of state, the gravitational wave background and the running of the spectral index of primordial perturbations. Using the latest Planck 2015 data release (with polarization), we found no significant indication for extensions to the standard Λ CDM scenario, with the notable exception of the angular power spectrum lensing amplitude, Alens , which is larger than the expected value at more than 2 standard deviations, even when combining the Planck data with BAO and supernovae type Ia external data sets. In our extended cosmological framework, we find that a combined Planck+BAO analysis constrains the value of the rms density fluctuation parameter to σ8=0.781-0.063+0.065 at 95 % C.L., helping to relieve the possible tensions with the CFHTlenS cosmic shear survey. We also find a lower value for the reionization optical depth τ =0.058-0.043+0.040 at 95 % C.L. with respect to the one derived under the assumption of Λ CDM . The scalar spectral index nS is now compatible with a Harrison-Zeldovich spectrum to within 2.5 standard deviations. Combining the Planck data set with the Hubble Space Telescope prior on the Hubble constant provides a value for the equation of state w <-1 at more than 2 standard deviations, while the neutrino effective number is fully compatible with the expectations of the standard three neutrino framework.
Late time acceleration in a non-commutative model of modified cosmology
Energy Technology Data Exchange (ETDEWEB)
Malekolkalami, B., E-mail: b.malakolkalami@uok.ac.ir [Department of Physics, University of Kurdistan, Pasdaran St., Sanandaj (Iran, Islamic Republic of); Atazadeh, K., E-mail: atazadeh@azaruniv.ac.ir [Department of Physics, Azarbaijan Shahid Madani University, 53714-161, Tabriz (Iran, Islamic Republic of); Vakili, B., E-mail: b-vakili@iauc.ac.ir [Department of Physics, Central Tehran Branch, Islamic Azad University, Tehran (Iran, Islamic Republic of)
2014-12-12
We investigate the effects of non-commutativity between the position–position, position–momentum and momentum–momentum of a phase space corresponding to a modified cosmological model. We show that the existence of such non-commutativity results in a Moyal Poisson algebra between the phase space variables in which the product law between the functions is of the kind of an α-deformed product. We then transform the variables in such a way that the Poisson brackets between the dynamical variables take the form of a usual Poisson bracket but this time with a noncommutative structure. For a power law expression for the function of the Ricci scalar with which the action of the gravity model is modified, the exact solutions in the commutative and noncommutative cases are presented and compared. In terms of these solutions we address the issue of the late time acceleration in cosmic evolution.
Cosmological perturbations of self-accelerating universe in nonlinear massive gravity
Gumrukcuoglu, A Emir; Mukohyama, Shinji
2011-01-01
We study cosmological perturbations of self-accelerating universe solutions in the recently proposed nonlinear theory of massive gravity, with general matter content. While the broken diffeomorphism invariance implies that there generically are 2 tensor, 2 vector and 2 scalar degrees of freedom in the gravity sector, we find that the scalar and vector degrees have vanishing kinetic terms and nonzero mass terms. Depending on their nonlinear behavior, this indicates either nondynamical nature of these degrees or strong couplings. Assuming the former, we integrate out the 2 vector and 2 scalar degrees of freedom. We then find that in the scalar and vector sectors, gauge-invariant variables constructed from metric and matter perturbations have exactly the same quadratic action as in general relativity. The difference from general relativity arises only in the tensor sector, where the graviton mass modifies the dispersion relation of gravitational waves, with a time-dependent effective mass. This may lead to modif...
Constraints on deviations from ΛCDM within Horndeski gravity
Bellini, Emilio; Cuesta, Antonio J.; Jimenez, Raul; Verde, Licia
2016-02-01
Recent anomalies found in cosmological datasets such as the low multipoles of the Cosmic Microwave Background or the low redshift amplitude and growth of clustering measured by e.g., abundance of galaxy clusters and redshift space distortions in galaxy surveys, have motivated explorations of models beyond standard ΛCDM. Of particular interest are models where general relativity (GR) is modified on large cosmological scales. Here we consider deviations from ΛCDM+GR within the context of Horndeski gravity, which is the most general theory of gravity with second derivatives in the equations of motion. We adopt a parametrization in which the four additional Horndeski functions of time αi(t) are proportional to the cosmological density of dark energy ΩDE(t). Constraints on this extended parameter space using a suite of state-of-the art cosmological observations are presented for the first time. Although the theory is able to accommodate the low multipoles of the Cosmic Microwave Background and the low amplitude of fluctuations from redshift space distortions, we find no significant tension with ΛCDM+GR when performing a global fit to recent cosmological data and thus there is no evidence against ΛCDM+GR from an analysis of the value of the Bayesian evidence ratio of the modified gravity models with respect to ΛCDM, despite introducing extra parameters. The posterior distribution of these extra parameters that we derive return strong constraints on any possible deviations from ΛCDM+GR in the context of Horndeski gravity. We illustrate how our results can be applied to a more general frameworks of modified gravity models.
International Nuclear Information System (INIS)
The Universe on large scales is well described by the ΛCDM cosmological model. There however remain some heavy clouds on our global understanding, especially on galaxy scales, which we review here. While some of these clouds might perhaps disappear through small compensatory adjustments of the model, such as changing the mass of the dark matter particles or accounting better for baryonic physics, others should rather be taken as strong indications that the physics of the dark sector is, at the very least, much richer and complex than currently assumed, and that our understanding of gravity and dynamics might also be at play. For instance, the empirically well-tested MOND phenomenology in galaxies, whatever its final explanation, should be understood in any model of galaxy formation and dynamics. Current alternatives to ΛCDM however bring with them many unsolved questions and challenges.
Beyond ΛCDM: Problems, solutions, and the road ahead
Bull, Philip
2016-01-01
Despite its continued observational successes, there is a persistent (and growing) interest in extending cosmology beyond the standard model, ΛCDM. This is motivated by a range of apparently serious theoretical issues, involving such questions as the cosmological constant problem, the particle nature of dark matter, the validity of general relativity on large scales, the existence of anomalies in the CMB and on small scales, and the predictivity and testability of the inflationary paradigm. I...
Ishak, Mustapha; Troxel, M A
2013-01-01
Probes of cosmic expansion constitute the main basis for arguments to support or refute a possible apparent acceleration due to uneven dynamics in the universe as described by inhomogeneous cosmological models. We present in this Letter a separate argument based on results from the study of the growth rate of large-scale structure in the universe as modeled by the Szekeres inhomogeneous cosmological models. We use the models in all generality with no assumptions of spherical or axial symmetries. We find that Szekeres inhomogeneous models that fit well the observed expansion history fail to explain the observed late-time suppression of the growth of structure unless a cosmological constant is added to the dynamics.
Born-Infeld cosmology with scalar Born-Infeld matter
Jana, Soumya
2016-01-01
Cosmology in Eddington-inspired Born-Infeld gravity is investigated using a scalar Born-Infeld field (eg. tachyon condensate) as matter. In this way, both in the gravity and matter sectors we have Born-Infeld-like structures characterised by their actions and via two separate constants, $\\kappa$ and $\\alpha_T^2$ respectively. With a particular choice of the form of $\\dot{\\phi}$ (time derivative of the Born-Infeld scalar), analytical cosmological solutions are found. Thereafter, we explore some of the unique features of the corresponding cosmological spacetimes. For $\\kappa>0$, our solution has a de Sitter-like expansion both at early and late times, with an intermediate deceleration sandwiched between the accelerating phases. On the other hand, when $\\kappa0$ solution, are as good as in $\\Lambda$CDM cosmology. However, the $\\kappa<0$ solution has to be discarded due to the occurrence of a bounce at an unacceptably low redshift.
Verde, Licia; Pigozzo, Cassio; Heavens, Alan F; Jimenez, Raul
2016-01-01
We investigate our knowledge of early universe cosmology by exploring how much additional energy density can be placed in different components beyond those in the $\\Lambda$CDM model. To do this we use a method to separate early- and late-universe information enclosed in observational data, thus markedly reducing the model-dependency of the conclusions. We find that the 95\\% credibility regions for extra energy components of the early universe at recombination are: non-accelerating additional fluid density parameter $\\Omega_{\\rm MR} < 0.006$ and extra radiation parameterised as extra effective neutrino species $2.3 < N_{\\rm eff} < 3.2$ when imposing flatness. Our constraints thus show that even when analyzing the data in this largely model-independent way, the possibility of hiding extra energy components beyond $\\Lambda$CDM in the early universe is seriously constrained by current observations. We also find that the standard ruler, the sound horizon at radiation drag, can be well determined in a way ...
Odintsov, S D
2016-01-01
We present some cosmological models which unify the late and early-time acceleration eras with the radiation and the matter domination era, and we realize the cosmological models by using the theoretical framework of $F(R)$ gravity. Particularly, the first model unifies the late and early-time acceleration with the matter domination era, and the second model unifies all the evolution eras of our Universe. The two models are described in the same way at early and late times, and only the intermediate stages of the evolution have some differences. Each cosmological model contains two Type IV singularities which are chosen to occur one at the end of the inflationary era and one at the end of the matter domination era. The cosmological models at early times are approximately identical to the $R^2$ inflation model, so these describe a slow-roll inflationary era which ends when the slow-roll parameters become of order one. The inflationary era is followed by the radiation era and after that the matter domination er...
Inflation and late-time acceleration from a double-well potential with cosmological constant
de Haro, Jaume; Elizalde, Emilio
2016-06-01
A model of a universe without big bang singularity is presented, which displays an early inflationary period ending just before a phase transition to a kination epoch. The model produces enough heavy particles so as to reheat the universe at temperatures in the MeV regime. After the reheating, it smoothly matches the standard Λ CDM scenario.
Beyond $\\Lambda$CDM: Problems, solutions, and the road ahead
Bull, Philip; Adamek, Julian; Baker, Tessa; Bellini, Emilio; Jiménez, Jose Beltrán; Bentivegna, Eloisa; Camera, Stefano; Clesse, Sébastien; Davis, Jonathan H; Di Dio, Enea; Enander, Jonas; Finelli, Fabio; Heavens, Alan; Heisenberg, Lavinia; Hu, Bin; Llinares, Claudio; Maartens, Roy; Mörtsell, Edvard; Nadathur, Seshadri; Noller, Johannes; Pasechnik, Roman; Pawlowski, Marcel S; Pereira, Thiago S; Quartin, Miguel; Ricciardone, Angelo; Riemer-Sørensen, Signe; Rinaldi, Massimiliano; Sakstein, Jeremy; Saltas, Ippocratis D; Salzano, Vincenzo; Sawicki, Ignacy; Solomon, Adam R; Spolyar, Douglas; Starkman, Glenn D; Steer, Danièle; Tereno, Ismael; Verde, Licia; Villaescusa-Navarro, Francisco; von Strauss, Mikael; Winther, Hans A
2015-01-01
Despite its continued observational successes, there is a persistent (and growing) interest in extending cosmology beyond the standard model, $\\Lambda$CDM. This is motivated by a range of apparently serious theoretical issues, involving such questions as the cosmological constant problem, the particle nature of dark matter, the validity of general relativity on large scales, the existence of anomalies in the CMB and on small scales, and the predictivity and testability of the inflationary paradigm. In this paper, we summarize the current status of $\\Lambda$CDM as a physical theory, and review investigations into possible alternatives along a number of different lines, with a particular focus on highlighting the most promising directions. While the fundamental problems are proving reluctant to yield, the study of alternative cosmologies has led to considerable progress, with much more to come if hopes about forthcoming high-precision observations and new theoretical ideas are fulfilled.
Beyond Λ CDM: Problems, solutions, and the road ahead
Bull, Philip; Akrami, Yashar; Adamek, Julian; Baker, Tessa; Bellini, Emilio; Beltrán Jiménez, Jose; Bentivegna, Eloisa; Camera, Stefano; Clesse, Sébastien; Davis, Jonathan H.; Di Dio, Enea; Enander, Jonas; Heavens, Alan; Heisenberg, Lavinia; Hu, Bin; Llinares, Claudio; Maartens, Roy; Mörtsell, Edvard; Nadathur, Seshadri; Noller, Johannes; Pasechnik, Roman; Pawlowski, Marcel S.; Pereira, Thiago S.; Quartin, Miguel; Ricciardone, Angelo; Riemer-Sørensen, Signe; Rinaldi, Massimiliano; Sakstein, Jeremy; Saltas, Ippocratis D.; Salzano, Vincenzo; Sawicki, Ignacy; Solomon, Adam R.; Spolyar, Douglas; Starkman, Glenn D.; Steer, Danièle; Tereno, Ismael; Verde, Licia; Villaescusa-Navarro, Francisco; von Strauss, Mikael; Winther, Hans A.
2016-06-01
Despite its continued observational successes, there is a persistent (and growing) interest in extending cosmology beyond the standard model, Λ CDM. This is motivated by a range of apparently serious theoretical issues, involving such questions as the cosmological constant problem, the particle nature of dark matter, the validity of general relativity on large scales, the existence of anomalies in the CMB and on small scales, and the predictivity and testability of the inflationary paradigm. In this paper, we summarize the current status of Λ CDM as a physical theory, and review investigations into possible alternatives along a number of different lines, with a particular focus on highlighting the most promising directions. While the fundamental problems are proving reluctant to yield, the study of alternative cosmologies has led to considerable progress, with much more to come if hopes about forthcoming high-precision observations and new theoretical ideas are fulfilled.
Institute of Scientific and Technical Information of China (English)
Lü Jian-Bo; Xu Li-Xin; Liu Mo-Lin; Gui Yuan-Xing
2009-01-01
In the framework of a five-dimensional(5D)bounce cosmological model,a useful function f(z)is obtained by giving a concrete expression of deceleration parameter q(z)=q1+q2/1+1n(1+z).Then usng the obtained Hubble parameter H(z)according to the function f(z),we constrain the accelerating universe from recent cosmic observations:the 192 ESSENCE SNe Ia and the 9 observational H(z)data.The best fitting values of transition redshift zT and current deceleration parameter q0 are given as zT=o.65±0.25-0.12 and q0=-0.76+0.15-0.15(1σ).Furthermore,in the 5D bounce model it can be seen that the evolution of equation of state(EOS)for dark energy ωde can cross over-1 at about z=0.23 and the current value ω0de=1.15＜-1.On the other hand,by giving a concrete expression of model-independent EOS of dark energy ωde,in the 5D bounce model we obtain the best fitting values zT=0.66+0311-0.08 and q0=-0.69+0.10-0.10(1σ)from the recently observed data:the 192 ESSENCE SNe Ia,the observational H(z)data,the 3-year Wilkinson Microwave Anisotropy Probe(WMAP),the Sloan Digital Sky Survey(SDSS)baryon acoustic peak and the x-ray gas mass fraction in clusters.
CDM Country Guide for The Philippines
International Nuclear Information System (INIS)
Under the Integrated Capacity Strengthening for the CDM (ICS-CDM) programme, IGES presents the CDM Country Guides, a series of manuals on CDM project development for Cambodia, China, India, Indonesia, the Philippines, and Thailand. These guidebooks aim at facilitating CDM project developments in Asia by providing essential information to both project developers and potential investors. This volume is on The Philippines
Cosmology with a time dependent cosmological constant
International Nuclear Information System (INIS)
In the context of the scalar-tensor theories we consider cosmological models with a time dependent cosmological constant. Several toy models are obtained among them there are solutions without singularity and accelerating. (Author)
Realistic coasting cosmology from the Milne model
John, Moncy V
2016-01-01
In the context of the recent synchronicity problem in $\\Lambda$CDM cosmology, coasting models such as the classic Milne model and the $R_h=ct$ model have attracted much attention. Also, a very recent analysis of supernovae Ia data is reported to favour models with constant expansion rates. We point out that the nonempty $R_h=ct$ model has some known antecedents in the literature. Some of these are published even before the discovery of the accelerated expansion and were shown to have none of the cosmological problems and also that $H_0t_0=1$ and $\\Omega_m/\\Omega_{dark \\; energy}$ = some constant of the order of unity. In this paper, we also derive such a model by a complex extension of scale factor in the Milne model.
Dissipative or conservative cosmology with dark energy?
International Nuclear Information System (INIS)
All evolutional paths for all admissible initial conditions of FRW cosmological models with dissipative dust fluid (described by dark matter, baryonic matter and dark energy) are analyzed using dynamical system approach. With that approach, one is able to see how generic the class of solutions leading to the desired property-acceleration-is. The theory of dynamical systems also offers a possibility of investigating all possible solutions and their stability with tools of Newtonian mechanics of a particle moving in a one-dimensional potential which is parameterized by the cosmological scale factor. We demonstrate that flat cosmology with bulk viscosity can be treated as a conservative system with a potential function of the Chaplygin gas type. We characterize the class of dark energy models that admit late time de Sitter attractor solution in terms of the potential function of corresponding conservative system. We argue that inclusion of dissipation effects makes the model more realistic because of its structural stability. We also confront viscous models with SNIa observations. The best fitted models are obtained by minimizing the χ2 function which is illustrated by residuals and χ2 levels in the space of model independent parameters. The general conclusion is that SNIa data supports the viscous model without the cosmological constant. The obtained values of χ2 statistic are comparable for both the viscous model and ΛCDM model. The Bayesian information criteria are used to compare the models with different power-law parameterization of viscous effects. Our result of this analysis shows that SNIa data supports viscous cosmology more than the ΛCDM model if the coefficient in viscosity parameterization is fixed. The Bayes factor is also used to obtain the posterior probability of the model
The velocity field in MOND cosmology
Candlish, G. N.
2016-08-01
The recently developed code for N-body/hydrodynamics simulations in Modified Newtonian Dynamics (MOND), known as RAYMOND, is used to investigate the consequences of MOND on structure formation in a cosmological context, with a particular focus on the velocity field. This preliminary study investigates the results obtained with the two formulations of MOND implemented in RAYMOND, as well as considering the effects of changing the choice of MOND interpolation function, and the cosmological evolution of the MOND acceleration scale. The simulations are contrived such that structure forms in a background cosmology that is similar to Λcold dark matter, but with a significantly lower matter content. Given this, and the fact that a fully consistent MOND cosmology is still lacking, we compare our results with a standard ΛCDM simulation, rather than observations. As well as demonstrating the effectiveness of using RAYMOND for cosmological simulations, it is shown that a significant enhancement of the velocity field is likely an unavoidable consequence of the gravitational modification implemented in MOND, and may represent a clear observational signature of such a modification. It is further suggested that such a signal may be clearest in intermediate-density regions such as cluster outskirts and filaments.
Guidebook to financing CDM projects
Energy Technology Data Exchange (ETDEWEB)
Kamel, S.
2007-07-01
One of the challenges facing Clean Development Mechanism (CDM) projects today is their limited ability to secure financing for the underlying greenhouse gas emission reduction activities, particularly in the least developed countries. Among the key reasons for this is the fact that most financial intermediaries in the CDM host countries have limited or no knowledge of the CDM Modalities and Procedures. Moreover, approaches, tools and skills for CDM project appraisal are lacking or are asymmetrical to the skills in comparable institutions in developed countries. Consequently, developing country financial institutions are unable to properly evaluate the risks and rewards associated with investing or lending to developers undertaking CDM projects, and therefore have, by-and-large, refrained from financing these projects. In addition, some potential project proponents lack experience in structuring arrangements for financing a project. This Guidebook - commissioned by the UNEP Risoe Centre as part of the activities of the Capacity Development for CDM (CD4CDM) project (http://www.cd4cdm.org) - addresses these barriers by providing information aimed at both developing country financial institutions and at CDM project proponents. It should be noted that while the Guidebook was developed particularly with the CDM in mind, most sections will also be relevant for Joint Implementation (JI) project activities. For more detailed information on JI modalities and procedures please consult: http://ji.unfccc.int The purpose of this Guidebook is two-fold: 1) To guide project developers on obtaining financing for the implementation of activities eligible under the CDM; and 2) To demonstrate to developing country financial institutions typical approaches and methods for appraising the viability of CDM projects and for optimally integrating carbon revenue into overall project financing. The target audiences for the Guidebook are therefore, primarily: 1) CDM project proponents in
Which spectral distortions does $\\Lambda$CDM actually predict?
Chluba, Jens
2016-01-01
Ever refined cosmological measurements have established the $\\Lambda$CDM concordance model, with the key cosmological parameters being determined to percent-level precision today. This allows us to make explicit predictions for the spectral distortions of the cosmic microwave background (CMB) created by various processes occurring in the early Universe. Here, we summarize all guaranteed CMB distortions and assess their total uncertainty within $\\Lambda$CDM. We also compare simple methods for approximating them, highlighting some of the subtle aspects when it comes to interpreting future distortion measurements. Under simplified assumptions, we briefly study how well a PIXIE-like experiment may measure the main distortion parameters (i.e., $\\mu$ and $y$). Next generation CMB spectrometers are expected to detect the distortion caused by reionization and structure formation at extremely high significance. They will also be able to constrain the small-scale power spectrum through the associated $\\mu$-distortion, ...
A new recipe for $\\Lambda$CDM
Sahni, Varun
2015-01-01
It is well known that a canonical scalar field is able to describe either dark matter or dark energy but not both. We demonstrate that a non-canonical scalar field can describe both dark matter and dark energy within a unified setting. We consider the simplest extension of the canonical Lagrangian ${\\cal L} \\propto X^\\alpha - \\Lambda$ with $\\alpha \\geq 1$. In this case the kinetic term in the Lagrangian behaves just like a perfect fluid, whereas the potential term is the cosmological constant. For very large values, $\\alpha \\gg 1$, the equation of state of the kinetic term drops to zero and the expansion rate of the universe mimicks $\\Lambda$CDM. The velocity of sound in this model, and the associated gravitational clustering, is sensitive to the value of $\\alpha$. For very large values of $\\alpha$ the clustering properties of our model resemble those of cold dark matter (CDM). But for smaller values of $\\alpha$, gravitational clustering on small scales is suppressed, and our model has properties resembling t...
Growth of perturbations in nonlocal gravity with non-$\\Lambda$CDM background
Park, Sohyun
2016-01-01
We re-analyze the nonlocal gravity model of Deser and Woodard which was proposed to account for the current phase of cosmic acceleration. We show that the growth of perturbations predicted by this nonlocal gravity model when its background evolution is fixed by some particular non-$\\Lambda$CDM models (models still consistent to the expansion history data) can be substantially lower than when its background is fixed by $\\Lambda$CDM. This can be seen when we consider the background expansion by a dark energy model with a slightly less negative equation of state with respect to cosmological constant. Our results hints towards a fact that the choice of the background expansion can play a crucial role how this nonlocal gravity model can fit the growth history data. While the growth data might show better consistency to GR models (among the background models we studied so far), it seems the nonlocal gravity model studied in this work is able to show comparable consistency to the growth data as well. Showing this co...
N-body simulations of coupled dark energy cosmologies
Baldi, Marco; Robbers, Georg; Springel, Volker
2008-01-01
If the accelerated expansion of the Universe at the present epoch is driven by a dark energy scalar field, there may well be a non-trivial coupling between the dark energy and the cold dark matter (CDM) fluid. Such interactions give rise to new features in cosmological structure growth, like an additional long-range attractive force between CDM particles, or variations of the dark matter particle mass with time. We have implemented these effects in the N-body code GADGET-2 and present results of a series of high-resolution N-body simulations where the dark energy component is directly interacting with the cold dark matter. As a consequence of the new physics, CDM and baryon distributions evolve differently both in the linear and in the nonlinear regime of structure formation. Already on large scales a linear bias develops between these two components, which is further enhanced by the nonlinear evolution. We also find, in contrast with previous work, that the density profiles of CDM halos are less concentrated...
Testing coupled dark energy models with their cosmological background evolution
van de Bruck, Carsten; Morrice, Jack
2016-01-01
We consider a cosmology in which dark matter and a quintessence scalar field responsible for the acceleration of the Universe are allowed to interact. Allowing for both conformal and disformal couplings, we perform a global analysis of the constraints on our model using Hubble parameter measurements, baryon acoustic oscillation distance measurements, and a Supernovae Type Ia data set. We find that the additional disformal coupling relaxes the conformal coupling constraints. Moreover we show that, at the background level, a disformal interaction within the dark sector is preferred to both $\\Lambda$CDM and uncoupled quintessence, hence favouring interacting dark energy.
On the evolution of the cosmic-mass-density contrast and the cosmological constant
Palle, D
2003-01-01
We study the evolution of the cosmic-mass-density contrast beyond the Robertson-Walker geometry including the small contribution of acceleration. We derive a second-order evolution equation for the density contrast within the spherical model for CDM collisionless fluid including the cosmological constant, the expansion and the non-vanishing vector of acceleration. While the mass-density is not seriously affected by acceleration, the mass-density contrast changes its shape at smaller redshifts even for a small amount of the acceleration parameter. This could help to resolve current controversial results in cosmology from measurements of WMAP, gravitational lensing, XMM X-ray cluster or type Ia supernovae data, etc.
Constraints on deviations from {\\Lambda}CDM within Horndeski gravity
Bellini, Emilio; Jimenez, Raul; Verde, Licia
2015-01-01
Recent anomalies found in cosmological datasets such as the low multipoles of the Cosmic Microwave Background or the low redshift amplitude and growth of clustering measured by e.g., abundance of galaxy clusters and redshift space distortions in galaxy surveys, have motivated explorations of models beyond standard {\\Lambda}CDM. Of particular interest are models where general relativity (GR) is modified on large cosmological scales. Here we consider deviations from {\\Lambda}CDM+GR within the context of Horndeski gravity, which is the most general theory of gravity with second derivatives in the equations of motion. We adopt a parametrization in which the four additional Horndeski functions of time {\\alpha}_i(t) are proportional to the cosmological density of dark energy {\\Omega}_DE(t). Constraints on this extended parameter space using a suite of state-of-the art cosmological observations are presented for the first time. Although the theory is able to accommodate the low multipoles of the Cosmic Microwave Bac...
Cosmological Shocks in Adaptive Mesh Refinement Simulations and the Acceleration of Cosmic Rays
Skillman, Samuel W.; O'Shea, Brian W.; Hallman, Eric J.; Burns, Jack O.; Michael L. Norman
2008-01-01
We present new results characterizing cosmological shocks within adaptive mesh refinement N-Body/hydrodynamic simulations that are used to predict non-thermal components of large-scale structure. This represents the first study of shocks using adaptive mesh refinement. We propose a modified algorithm for finding shocks from those used on unigrid simulations that reduces the shock frequency of low Mach number shocks by a factor of ~3. We then apply our new technique to a large, (512 Mpc/h)^3, ...
Gravitational Lensing by CDM Halos: Singular versus Nonsingular Profiles
Martel, H; Martel, Hugo; Shapiro, Paul R.
2003-01-01
The gravitational lensing properties of cosmological halos depend upon the mass distribution within each halo. The description of halos as nonsingular, truncated isothermal spheres, a particular solution of the isothermal Lane-Emden equation (suitably modified for Lambda nonzero), has proved to be a useful approximation for the halos which form from realistic initial conditions in a CDM universe. The nonsingular TIS model reproduces many of the quantitative features of the N-body results for CDM halos, except in the very center, where CDM N-body halos show density profiles which vary as rho ~ r^(-alpha), alpha>1, instead of a small flat core. Possible discrepancies between these cuspy halo predictions of the CDM N-body simulations and observations of the inner mass profiles of dwarf and LSB disk galaxies based upon their rotation curves and of clusters based upon strong lensing measurements have led to a search for other diagnostics. A description of the lensing by TIS halos would be useful in this regard, as...
The Local Void: for or against $\\Lambda$CDM?
Xie, Lizhi; Guo, Qi
2014-01-01
The emptiness of the Local Void has been put forward as a serious challenge to the current standard paradigm of structure formation in $\\Lambda$CDM. We use a high resolution cosmological N-body simulation, the Millennium-II run, combined with a sophisticated semi-analytical galaxy formation model, to explore statistically whether the local void is allowed within our current knowledge of galaxy formation in $\\Lambda$CDM. We find that about $15$ percent of the Local Group analogue systems ($11$ of $77$) in our simulation are associated with nearby low density regions having size and 'emptiness' similar to those of the observed Local Void. This suggests that, rather than a crisis of the $\\Lambda$CDM, the emptiness of the Local Void is indeed a success of the standard $\\Lambda$CDM theory. The paucity of faint galaxies in such voids results from a combination of two factors: a lower amplitude of the halo mass function in the voids than in the field, and a lower galaxy formation efficiency in void haloes due to hal...
Relativistic perturbations in $\\Lambda$CDM: Eulerian & Lagrangian approaches
Villa, Eleonora
2016-01-01
We study the relativistic dynamics of a pressure-less and irrotational fluid of dark matter (CDM) with a cosmological constant ($\\Lambda$), up to second order in cosmological perturbation theory. In our analysis we also account for primordial non-Gaussianity. We consider three gauges: the synchronous-comoving gauge, the Poisson gauge and the total matter gauge, where the first is the unique relativistic Lagrangian frame of reference, and the latters are convenient choices for Eulerian frames. Our starting point is the metric and fluid variables in the Poisson gauge. We then perform a gauge-transformation to the synchronous-comoving gauge, and subsequently to the total matter gauge. Our expressions for the metrics, densities, velocities, and the gauge generators are novel and coincide with known results in the limit of a vanishing cosmological constant.
Accelerated Cosmological Models in Modified Gravity tested by distant Supernovae SNIa data
Borowiec, Andrzej; Godlowski, Wlodzimierz; Szydlowski, Marek
2006-01-01
Recent supernovae of type Ia measurements and other astronomical observations suggest that our universe is in accelerating phase of evolution at the present epoch. While a dark energy of unknown form is usually proposed as the most feasible mechanism for the acceleration, there are appears some alternative conception that some effects arising from generalization of Einstein equation can mimic dark energy through a modified Friedmann equation. In this work we investigate some observational con...
Dynamical system approach to running $\\Lambda$ cosmological models
Stachowski, Aleksander
2016-01-01
We discussed the dynamics of cosmological models in which the cosmological constant term is a time dependent function through the scale factor $a(t)$, Hubble function $H(t)$, Ricci scalar $R(t)$ and scalar field $\\phi(t)$. We considered five classes of models; two non-covariant parametrization of $\\Lambda$: 1) $\\Lambda(H)$CDM cosmologies where $H(t)$ is the Hubble parameter, 2) $\\Lambda(a)$CDM cosmologies where $a(t)$ is the scale factor, and three covariant parametrization of $\\Lambda$: 3) $\\Lambda(R)$CDM cosmologies, where $R(t)$ is the Ricci scalar, 4) $\\Lambda(\\phi)$-cosmologies with diffusion, 5) $\\Lambda(X)$-cosmologies, where $X=\\frac{1}{2}g^{\\alpha\\beta}\
DEFF Research Database (Denmark)
Brandt, Urs Steiner; Svendsen, Gert Tinggaard
2013-01-01
CDM projects have large potentials but also face significant obstacles that have so far limited their applicability. Two serious problems that an effective contracting faces are the presence of private information and the lack of sufficiently precise output measures. In a principal-agent framewor...
Issues related to a programme of activities under the CDM
Energy Technology Data Exchange (ETDEWEB)
Ellis, J.
2006-05-15
Emissions of CO2 from the energy and land-use change and forestry sectors are responsible for the majority of emissions in non-Annex I Parties to the UNFCCC. Tackling greenhouse gas (GHG) emissions from these sectors is a key to slowing the growth in GHG emissions in non-Annex I countries. Implementing Clean Development Mechanism (CDM) projects can help achieve this aim, while also assisting non-Annex I countries to move towards sustainable development and Annex I countries achieve their emission commitments under the Kyoto Protocol. There has been rapid progress in the CDM over the last year - in terms of the number of projects in the pipeline and registered, and in terms of credits issued. However, some important sectors are notable by their small share in the CDM portfolio. Several countries have also called attention to the need to accelerate the process of approving CDM methodologies and projects. In order to improve the effectiveness of the CDM to achieve its dual objectives, the COP/MOP agreed a decision on 'further guidance relating to the clean development mechanism. This decision lays out guidance on how to improve the operation of the CDM, and includes provisions that allow: (1) Bundling of project activities; and (2) Project activities under a programme of activities, to be registered as a CDM project activity. At present, of the 172 currently registered CDM project activities, 27 involve programmes or bundles. These project activities can include more than one project type, be implemented in several locations, and/or occur in more than one sector. This paper assesses how project activities under a programme of activities under the CDM (referred to here as PCDM) could help to increase the effectiveness of the CDM by encouraging a wide spread of emission mitigation activities. This paper also explores the key issues that may need to be considered for the PCDM concept to be further implemented. The paper concludes that: (1) Key concepts and issues
Can background cosmology hold the key for modified gravity tests?
Ceron-Hurtado, Juan J; Li, Baojiu
2016-01-01
Modified gravity theories are a popular alternative to dark energy as a possible explanation for the observed accelerating cosmic expansion, and their cosmological tests are currently an active research field. Studies in recent years have been increasingly focused on testing these theories in the nonlinear regime, which is computationally demanding. Here we show that, under certain circumstances, a whole class of theories can be ruled out by using background cosmology alone. This is possible because certain classes of models (i) are fundamentally incapable of producing specific background expansion histories, and (ii) said histories are incompatible with local gravity tests. As an example, we demonstrate that a popular class of models, $f(R)$ gravity, would not be viable if observations suggest even a slight deviation of the background expansion history from that of the $\\Lambda$CDM paradigm.
Can background cosmology hold the key for modified gravity tests?
Ceron-Hurtado, Juan J.; He, Jian-hua; Li, Baojiu
2016-09-01
Modified gravity theories are a popular alternative to dark energy as a possible explanation for the observed accelerating cosmic expansion, and their cosmological tests are currently an active research field. Studies in recent years have been increasingly focused on testing these theories in the nonlinear regime, which is computationally demanding. Here we show that, under certain circumstances, a whole class of theories can be ruled out by using background cosmology alone. This is possible because certain classes of models (i) are fundamentally incapable of producing specific background expansion histories, and (ii) said histories are incompatible with local gravity tests. As an example, we demonstrate that a popular class of models, f (R ) gravity, would not be viable if observations suggest even a slight deviation of the background expansion history from that of the Λ CDM paradigm.
Acceleration of the universe: a reconstruction of the effective equation of state
Mukherjee, Ankan
2016-01-01
The present work is based upon a parametric reconstruction of the effective or total equation of state in a model for the universe with accelerated expansion. The constraints on the model parameters are obtained by maximum likelihood analysis using the supernova distance modulus data, observational Hubble data, baryon acoustic oscillation data and cosmic microwave background shift parameter data. For statistical comparison, the same analysis has also been carried out for the wCDM dark energy model. Different model selection criteria (Akaike information criterion (AIC)) and (Bayesian Information Criterion (BIC)) give the clear indication that the reconstructed model is well consistent with the wCDM model. Then both the models (w_{eff}(z) model and wCDM model) have also been presented through (q_0 ,j_0 ) parameter space. Tighter constraint on the present values of dark energy equation of state parameter (w_{DE}(z = 0)) and cosmological jerk (j_0) have been achieved for the reconstructed model.
The bulk viscous string cosmology in an anisotropic universe with late time acceleration
Institute of Scientific and Technical Information of China (English)
Hassan Amirhashchi
2013-01-01
A model of a cloud formed by massive strings is used as a source of Bianchi type Ⅱ cases.We assume that the expansion (θ) in the model is proportional to the shear (σ).To get an exact solution,we consider the equation of state of the fluid to be in the stiff form.It is found that the bulk viscosity played a very important role in the history of the universe.In the presence of bulk viscosity the particles dominate over strings whereas in the absence of it,strings dominate over the particles,which is not consistent with recent observations.Also we observe that the viscosity causes the expansion of the universe to be accelerating.Our models are evolving from an early decelerating phase to a late time accelerating phase.The physical and geometrical behaviors of these models are discussed.
Thermodynamics properties of tachyon cosmology with non-minimal coupling to matter
Farajollahi, H; Abolghasemi, M
2016-01-01
Recently, we have investigated the dynamics of the universe in tachyon cosmology with non-minimal coupling to matter \\cite{faraj}-\\cite{faraj3}. In particular, for the interacting holographic dark energy (IHDE), the model is studied in \\cite{Ravanpak}. In the current work, a significant observational program has been conducted to unveil the model's thermodynamic properties. Our result shows that the IHDE version of our model better fits the observational data than $\\Lambda$CDM model. The first and generalized second thermodynamics laws for the universe enveloped by cosmological apparent and event horizon are revisited. From the results, both first and generalized second laws, constrained by the observational data, are satisfied on cosmological apparent horizon.In addition, the total entropy is verified with the observation only if the horizon of the universe is taken as apparent horizon. Then, due to validity of generalized second law, the current cosmic acceleration is also predicted.
Dipolar Dark Matter and Cosmology
Blanchet, Luc; Tiec, Alexandre Le; Marsat, Sylvain
2013-01-01
The phenomenology of the modified Newtonian dynamics (MOND) can be recovered from a mechanism of "gravitational polarization" of some dipolar medium playing the role of dark matter. We review a relativistic model of dipolar dark matter (DDM) within standard general relativity to describe, at some effective level, a fluid polarizable in a gravitational field. At first order in cosmological perturbation theory, this model is equivalent to the concordance cosmological scenario, or Lambda-cold dark matter (CDM) model. At second order, however, the internal energy of DDM modifies the curvature perturbation generated by CDM. This correction, which depends quadratically on the dipole, induces a new type of non-Gaussianity in the bispectrum of the curvature perturbation with respect to standard CDM. Recent observations by the Planck satellite impose stringent constraints on the primordial value of the dipole field.
Maps of CMB lensing deflection from N-body simulations in Coupled Dark Energy Cosmologies
Energy Technology Data Exchange (ETDEWEB)
Carbone, Carmelita [INAF – Osservatorio Astronomico di Brera, Via Bianchi 46, I-23807 Merate (Italy); Baldi, Marco [Dipartimento di Fisica e Astronomia, Università di Bologna, Viale B. Pichat 6/2, I-40127 Bologna (Italy); Pettorino, Valeria [Département de Physique Théorique and Center for Astroparticle Physics, Université de Genève, 24 quai Ernest Ansermet, CH–1211 Genève 4 (Switzerland); Baccigalupi, Carlo, E-mail: carmelita.carbone@brera.inaf.it, E-mail: marco.baldi5@unibo.it, E-mail: valeria.pettorino@unige.ch, E-mail: bacci@sissa.it [SISSA, Via Bonomea 265, Trieste, I-34136 (Italy)
2013-09-01
We produce lensing potential and deflection-angle maps in order to simulate the weak gravitational lensing of the Cosmic Microwave Background (CMB) via ray-tracing through the COupled Dark Energy Cosmological Simulations (CoDECS), the largest suite of N-body simulations to date for interacting Dark Energy cosmologies. The constructed maps faithfully reflect the N-body cosmic structures on a range of scales going from the arcminute to the degree scale, limited only by the resolution and extension of the simulations. We investigate the variation of the lensing pattern due to the underlying Dark Energy (DE) dynamics, characterised by different background and perturbation behaviours as a consequence of the interaction between the DE field and Cold Dark Matter (CDM). In particular, we study in detail the results from three cosmological models differing in the background and perturbations evolution at the epoch in which the lensing cross section is most effective, corresponding to a redshift of ∼ 1, with the purpose to isolate their imprints in the lensing observables, regardless of the compatibility of these models with present constraints. The scenarios investigated here include a reference ΛCDM cosmology, a standard coupled DE (cDE) scenario, and a ''bouncing'' cDE scenario. For the standard cDE scenario, we find that typical differences in the lensing potential result from two effects: the enhanced growth of linear CDM density fluctuations with respect to the ΛCDM case, and the modified nonlinear dynamics of collapsed structures induced by the DE-CDM interaction. As a consequence, CMB lensing highlights the DE impact in the cosmological expansion, even in the degenerate case where the amplitude of the linear matter density perturbations, parametrised through σ{sub 8}, is the same in both the standard cDE and ΛCDM cosmologies. For the ''bouncing'' scenario, we find that the two opposite behaviours of the lens density
Non-minimal derivative coupling gravity in cosmology
Gumjudpai, Burin
2015-01-01
We give a brief review of the non-minimal derivative coupling (NMDC) scalar field theory in which there is non-minimal coupling between the scalar field derivative term and the Einstein tensor. We assume that the expansion is of power-law type or super-acceleration type for small redshift. The Lagrangian includes the NMDC term, a free kinetic term, a cosmological constant term and a barotropic matter term. For a value of the coupling constant that is compatible with inflation, we use the combined WMAP9 (WMAP9+eCMB+BAO+ $H_0$) dataset, the PLANCK+WP dataset, and the PLANCK $TT,TE,EE$+lowP+Lensing+ext datasets to find the value of the cosmological constant in the model. Modeling the expansion with power-law gives a negative cosmological constants while the phantom power-law (super-acceleration) expansion gives positive cosmological constant with large error bar. The value obtained is of the same order as in the $\\Lambda$CDM model, since at late times the NMDC effect is tiny due to small curvature.
Non-minimal derivative coupling gravity in cosmology
Gumjudpai, Burin; Rangdee, Phongsaphat
2015-11-01
We give a brief review of the non-minimal derivative coupling (NMDC) scalar field theory in which there is non-minimal coupling between the scalar field derivative term and the Einstein tensor. We assume that the expansion is of power-law type or super-acceleration type for small redshift. The Lagrangian includes the NMDC term, a free kinetic term, a cosmological constant term and a barotropic matter term. For a value of the coupling constant that is compatible with inflation, we use the combined WMAP9 (WMAP9 + eCMB + BAO + H_0) dataset, the PLANCK + WP dataset, and the PLANCK TT, TE, EE + lowP + Lensing + ext datasets to find the value of the cosmological constant in the model. Modeling the expansion with power-law gives a negative cosmological constants while the phantom power-law (super-acceleration) expansion gives positive cosmological constant with large error bar. The value obtained is of the same order as in the Λ CDM model, since at late times the NMDC effect is tiny due to small curvature.
Dynamical Vacuum against a rigid Cosmological Constant
Sola, Joan; Gomez-Valent, Adria; Nunes, Rafael C
2016-01-01
When we are approaching the centenary of the introduction of the cosmological constant $\\Lambda$ by Einstein in his gravitational field equations, and after about two decades of the first observational papers confirming the existence of a non-vanishing, positive, $\\Lambda$ as the most likely explanation for the observed acceleration of the Universe, we are still facing the question whether $\\Lambda$ is truly a fundamental constant of Nature or a mildly evolving dynamical variable. In this work we compare three types of cosmological scenarios involving dynamical vacuum energy in interaction with matter. By performing an overall fit to the cosmological observables $SNIa+BAO+H(z)+LSS+CMB$, we find that the dynamical $\\Lambda$ models are significantly more favored than the $\\Lambda$CDM, suggesting that a rigid $\\Lambda$-term is excluded at $\\sim 3\\sigma$ c.l. This conclusion is strongly supported by Akaike and Bayesian information criteria which render more than 10 points of difference in favor of the dynamical v...
The possibility of an accelerating cosmology in Rastall's theory
Energy Technology Data Exchange (ETDEWEB)
Capone, M [Dipartimento di Matematica, Universita di Torino, Via Carlo Alberto 10, 10125 - Torino (Italy); Cardone, V F [Dipartimento di Fisica Generale ' Amedeo Avogadro' , Universita di Torino, Via Pietro Giuria 1, 10125 - Torino (Italy); Ruggiero, M L, E-mail: monica.capone@unito.i [UTIU, Universita Telematica Internazionale Uninettuno, Corso Vittorio Emanuele II 39, 00186 - Roma (Italy)
2010-04-01
In an attempt to look for a viable mechanism leading to a present day accelerated expansion, we investigate the possibility that the observed cosmic speed up may be recovered in the framework of the Rastall's theory, relying on the non-conservativity of the stress-energy tensor, i.e. T{sup {mu}}{sub v;{mu}} {ne} 0. We derive the modified Friedmann equations and show that they correspond to Cardassian-like equations. We also show that, under suitable assumptions on the equation of state of the matter term sourcing the gravitational field, it is indeed possible to get an accelerated expansion, in agreement with the Hubble diagram of both Type Ia Supernovae (SNeIa) and Gamma Ray Bursts (GRBs). Unfortunately, to achieve such a result one has to postulate a matter density parameter larger than the typical {Omega}{sub M} {approx_equal} 0.3 value inferred from cluster gas mass fraction data. As a further issue, we discuss the possibility to retrieve the Rastall's theory from a Palatini variational principle approach to f(R) gravity. However, such an attempt turns out to be unsuccessful.
Directory of Open Access Journals (Sweden)
Lorenzo Iorio
2014-01-01
Full Text Available By phenomenologically assuming a slow temporal variation of the percent acceleration rate S̈S -1 of the cosmic scale factor S(t, it is shown that the orbit of a local binary undergoes a secular expansion. To first order in the power expansion of S̈S -1 around the present epoch t0, a non-vanishing shift per orbit (Δr of the two-body relative distance r occurs for eccentric trajectories. A general relativistic expression, which turns out to be cubic in the Hubble parameter H0 at the present epoch, is explicitly calculated for it in the case of matter-dominated epochs with Dark Energy. For a highly eccentric Oort comet orbit with period Pb ≈ 31 Myr, the general relativistic distance shift per orbit turns out to be of the order of (Δr ≈ 70 km. For the Large Magellanic Cloud, assumed on a bound elliptic orbit around the Milky Way, the shift per orbit is of the order of (Δr ≈ 2–4 pc. Our result has a general validity since it holds in any cosmological model admitting the Hubble law and a slowly varying S̈S-1(t. More generally, it is valid for an arbitrary Hooke-like extra-acceleration whose “elastic” parameter κ is slowly time-dependent, irrespectively of the physical mechanism which may lead to it. The coefficient κ1 of the first-order term of the power expansion of κ(t can be preliminarily constrained in a model-independent way down to a κ1 ≲ 2 x 10-13 year-3 level from latest Solar System’s planetary observations. The radial velocities of the double lined spectroscopic binary ALPHA Cen AB yield κ1 ≲ 10-8 year-3.
Wu, S Q
2001-01-01
The Hawking radiation of Dirac particles in an arbitrarily rectilinearly accelerating Kinnersley black hole with electro-magnetic charge and cosmological constant is investigated by using method of the generalized tortoise coordinate transformation. Both the location and the temperature of the event horizon depend on the time and the polar angle. The Hawking thermal radiation spectrum of Dirac particles is also derived. PACS numbers: 04.70.Dy, 97.60.Lf
Ishak, Mustapha; Whittington, Delilah; Garred, David
2007-01-01
We use the Szekeres inhomogeneous relativistic models in order to fit supernova combined data sets. We show that with a choice of the spatial curvature function that is guided by current observations, the models fit the supernova data as well as the LCDM model without requiring any dark energy component. The Szekeres models were originally derived as an exact solution to Einstein's equations with a general metric that has no symmetries and are regarded in the field as good candidates to represent the true lumpy universe that we observe. The best fit model found is also consistent with the requirement of spatial flatness at CMB scales. While more work remains, the result presented in this first paper appears to support the possibility of apparent acceleration.
Observational constraints on cosmological models with Chaplygin gas and quadratic equation of state
Sharov, G. S.
2016-06-01
Observational manifestations of accelerated expansion of the universe, in particular, recent data for Type Ia supernovae, baryon acoustic oscillations, for the Hubble parameter H(z) and cosmic microwave background constraints are described with different cosmological models. We compare the ΛCDM, the models with generalized and modified Chaplygin gas and the model with quadratic equation of state. For these models we estimate optimal model parameters and their permissible errors with different approaches to calculation of sound horizon scale rs(zd). Among the considered models the best value of χ2 is achieved for the model with quadratic equation of state, but it has 2 additional parameters in comparison with the ΛCDM and therefore is not favored by the Akaike information criterion.
WarmAndFuzzy: the halo model beyond CDM
Marsh, David J E
2016-01-01
Cold dark matter (CDM) is a well established paradigm to describe cosmological structure formation, and works extraordinarily well on large, linear, scales. Progressing further in dark matter physics requires being able to understand structure formation in the non-linear regime, both for CDM and its alternatives. This short note describes a calculation, and accompanying code, WarmAndFuzzy, incorporating the popular models of warm and fuzzy dark matter (WDM and FDM) into the standard halo model to compute the non-linear matter power spectrum. The FDM halo model power spectrum has not been computed before. The FDM implementation models ultralight axions and other scalar fields with $m_a\\approx 10^{-22}\\text{ eV}$. The WDM implementation models thermal WDM with mass $m_X\\approx 1\\text{ keV}$. The halo model shows that differences between WDM, FDM, and CDM survive at low redshifts in the quasi-linear and fully non-linear regimes. The code uses analytic transfer functions for the linear power spectrum, modified co...
Cosmological constraints for an Eddington-Born-Infeld field
De Felice, Antonio; Jhingan, Sanjay
2012-01-01
We consider the Eddington-Born-Infeld (EBI) model here without assuming any cosmological constant. The EBI scalar field is supposed to play a role of both dark matter and dark energy. Different eras in cosmology are reconstructed for the model. A comparison is drawn with $\\Lambda$CDM model using Supernova Ia, WMAP7 and BAO data. It seems that the EBI field in this form does not give good fit to observational data in comparison to the $\\Lambda$CDM model.
Fast cosmological parameter estimation using neural networks
Auld, T; Hobson, M P; Gull, S F
2006-01-01
We present a method for accelerating the calculation of CMB power spectra, matter power spectra and likelihood functions for use in cosmological parameter estimation. The algorithm, called CosmoNet, is based on training a multilayer perceptron neural network and shares all the advantages of the recently released Pico algorithm of Fendt & Wandelt, but has several additional benefits in terms of simplicity, computational speed, memory requirements and ease of training. We demonstrate the capabilities of CosmoNet by computing CMB power spectra over a box in the parameter space of flat \\Lambda CDM models containing the 3\\sigma WMAP1 confidence region. We also use CosmoNet to compute the WMAP3 likelihood for flat \\Lambda CDM models and show that marginalised posteriors on parameters derived are very similar to those obtained using CAMB and the WMAP3 code. We find that the average error in the power spectra is typically 2-3% of cosmic variance, and that CosmoNet is \\sim 7 \\times 10^4 faster than CAMB (for flat ...
Accelerating f(T) gravity models constrained by recent cosmological data
Cardone, Vincenzo F; Camera, Stefano
2012-01-01
Generalised Teleparallel gravity, also referred to as f(T) gravity, has been recently proposed as an extended theory of gravitation able to give rise to an accelerated expansion in a matter only universe. The cosmic speed up is driven by an effective torsion fluid whose equation of state depend on the f(T) function entering the modified gravity Lagrangian. We focus on two particular choices for f(T) which share the nice property to emulate a phantom divide crossing as suggested by some recent data. We check their viability contrasting the predicted background dynamics to the Hubble diagram as traced by both Type Ia Supernovae (SNeIa) and Gamma Ray Bursts (GRBs), the measurement of the rate expansion H(z), the Baryon Acoustic Oscillations (BAOs) at different redshifts, and the Cosmic Microwave Background Radiation (CMBR) distance priors. Both f(T) models turn out to be in very good agreement with this large dataset so that we also investigate whether it is possible to discriminate among them relying on the dif...
Exact solutions for scalar field cosmology in f(R) gravity
Maharaj, S D; Chervon, S V; Nikolaev, A V
2016-01-01
We look for exact solutions in scalar field cosmology. To achieve this we use $f(R)$ modified gravity with a scalar field and do not specify the the form of the $f(R)$ function. In particular, we study Friedmann universe assuming that acceleration of the scalar curvature is negligible. We first present solutions for special cases and then the general solution. Using initial conditions which represent the universe at the present epoch, we evaluated the constants of integration. This allows for the comparison of the scale factor in the new solutions with that of the $\\Lambda CDM$ solution, thereby affecting the age of the universe in $f(R)$ gravity.
Which spectral distortions does ΛCDM actually predict?
Chluba, Jens
2016-07-01
Ever refined cosmological measurements have established the ΛCDM concordance model, with the key cosmological parameters being determined to per cent-level precision today. This allows us to make explicit predictions for the spectral distortions of the cosmic microwave background (CMB) created by various processes occurring in the early Universe. Here, we summarize all guaranteed CMB distortions and assess their total uncertainty within ΛCDM. We also compare simple methods for approximating them, highlighting some of the subtle aspects when it comes to interpreting future distortion measurements. Under simplified assumptions, we briefly study how well a PIXIE-like experiment may measure the main distortion parameters (i.e. μ and y). Next-generation CMB spectrometers are expected to detect the distortion caused by reionization and structure formation at extremely high significance. They will also be able to constrain the small-scale power spectrum through the associated μ-distortion, improving limits on running of the spectral index. Distortions from the recombination era, adiabatic cooling of matter relative to the CMB and dark matter annihilation require a higher sensitivity than PIXIE in its current design. The crucial next step is an improved modelling of foregrounds and instrumental aspects, as we briefly discuss here.
Primer on CDM programme of activities
Energy Technology Data Exchange (ETDEWEB)
Hinostroza, M. (UNEP Risoe Centre, Roskilde (Denmark)); Lescano, A.D. (A2G Carbon Partners (Peru)); Alvarez, J.M. (Ministerio del Ambiente del Peru (Peru)); Avendano, F.M. (EEA Fund Management Ltd. (United Kingdom)
2009-07-01
As an advanced modality introduced in 2005, the Programmatic CDM (POA) is expected to address asymmetries of participation, especially of very small-scale project activities in certain areas, key sectors and many countries with considerable potential for greenhouse gas emission reductions, not reached by the traditional single-project-based CDM. Latest experiences with POAs and the recently finalized official guidance governing the Programmatic CDM are the grassroots of this Primer, which has the purpose of supporting the fully understanding of rules and procedures of POAs by interpreting them and analyzing real POA cases. Professional and experts from the public and private entities have contributed to the development of this Primer, produced by the UNEP Risoe Centre, as part of knowledge support activities for the Capacity Development for the CDM (CD4CDM) project. The overall objective of the CD4CDM is to develop the capacities of host countries to identify, design, approve, finance, implement CDM projects and commercialize CERs in participating countries. The CDM4CDM is funded by the Netherlands Ministry of Foreign Affairs. (author)
Grand Banquet of CDM for Power Enterprises
Institute of Scientific and Technical Information of China (English)
Peng Yuanchang; Jin Wen
2007-01-01
@@ The Kyoto Protocol was taken into effect on Feb. 16, 2005. It requires developed countries to reduce their greenhouse gas emissions, but it doesn't set binding limits on developing countries, such as China. The developed countries found that it is more cost-effective to reduce the emissions in developing countries than in their own. Therefore, the CDM emerged as the times require. Due to unfamiliarity and complicatedness, Chinese enterprises had been hesitating and taking wait-and-see attitude toward CDM, but they couldn't resist the attraction of free dinner of CDM, more and more enterprises started to attend the grand banquet of CDM since 2006.
Chavanis, Pierre-Henri
2013-01-01
We develop a cosmological model based on a quadratic equation of state p/c^2=-(\\alpha+1){\\rho^2}/{\\rho_P}+\\alpha\\rho-(\\alpha+1)\\rho_{\\Lambda} (where \\rho_P is the Planck density and \\rho_{\\Lambda} the cosmological density) "unifying" vacuum energy and dark energy in the spirit of a generalized Chaplygin gas model. For $\\rho\\rightarrow \\rho_P$, it reduces to p=-\\rho c^2 leading to a phase of early accelerated expansion (early inflation) with a constant density equal to the Planck density \\rho_P (vacuum energy). For $\\rho_{\\Lambda}\\ll\\rho\\ll \\rho_P$, we recover the standard linear equation of state p=\\alpha \\rho c^2 describing radiation (\\alpha=1/3) or pressureless matter (\\alpha=0) and leading to an intermediate phase of decelerating expansion. For $\\rho\\rightarrow \\rho_{\\Lambda}$, we get p=-\\rho c^2 leading to a phase of late accelerated expansion (late inflation) with a constant density equal to the cosmological density \\rho_{\\Lambda} (dark energy). We show a nice symmetry between the early universe (vacuum ...
The HII Galaxy Hubble Diagram Strongly Favors Rh = ct over ΛCDM
Wei, Jun-Jie; Wu, Xue-Feng; Melia, Fulvio
2016-08-01
We continue to build support for the proposal to use HII galaxies (HIIGx) and giant extragalactic HII regions (GEHR) as standard candles to construct the Hubble diagram at redshifts beyond the current reach of Type Ia supernovae. Using a sample of 25 high-redshift HIIGx, 107 local HIIGx, and 24 GEHR, we confirm that the correlation between the emission-line luminosity and ionized-gas velocity dispersion is a viable luminosity indicator, and use it to test and compare the standard model ΛCDM and the Rh = ct Universe by optimizing the parameters in each cosmology using a maximization of the likelihood function. For the flat ΛCDM model, the best fit is obtained with Ω _m= 0.40_{-0.09}^{+0.09}. However, statistical tools, such as the Akaike (AIC), Kullback (KIC) and Bayes (BIC) Information Criteria favor Rh = ct over the standard model with a likelihood of ≈94.8% - 98.8% versus only ≈1.2% - 5.2%. For wCDM (the version of ΛCDM with a dark-energy equation of state wde ≡ pde/ρde rather than wde = wΛ = -1), a statistically acceptable fit is realized with Ω _m=0.22_{-0.14}^{+0.16} and w_de= -0.51_{-0.25}^{+0.15} which, however, are not fully consistent with their concordance values. In this case, wCDM has two more free parameters than Rh = ct, and is penalized more heavily by these criteria. We find that Rh = ct is strongly favored over wCDM with a likelihood of ≈92.9% - 99.6% versus only 0.4% - 7.1%. The current HIIGx sample is already large enough for the BIC to rule out ΛCDM/wCDM in favor of Rh = ct at a confidence level approaching 3σ.
Born-Infeld cosmology with scalar Born-Infeld matter
Jana, Soumya; Kar, Sayan
2016-09-01
Cosmology in Eddington-inspired Born-Infeld gravity is investigated using a scalar Born-Infeld field (e.g. tachyon condensate) as matter. In this way, both in the gravity and matter sectors we have Born-Infeld-like structures characterized by their actions and via two separate constants, κ and αT2 , respectively. With a particular choice of the form of ϕ ˙ (the time derivative of the Born-Infeld scalar), analytical cosmological solutions are found. Thereafter, we explore some of the unique features of the corresponding cosmological spacetimes. For κ >0 , our solution has a de Sitter-like expansion both at early and late times, with an intermediate deceleration sandwiched between the accelerating phases. On the other hand, when κ data—a fact we demonstrate explicitly. The estimated properties of the Universe obtained from the fitting of the κ >0 solution are as good as in Λ CDM cosmology. However, the κ <0 solution has to be discarded due to the occurrence of a bounce at an unacceptably low redshift.
Energy Technology Data Exchange (ETDEWEB)
Curnow, P. (Baker and McKenzie, London (United Kingdom)); Hodes, G. (UNEP Risoe Centre on Energy, Climate and Sustainable Development, DTU, Roskilde (Denmark))
2009-08-15
The Clean Development Mechanism (CDM) continues to evolve organically, and many legal issues remain to be addressed in order to maximise its effectiveness. This Guidebook explains through case studies how domestic laws and regulatory frameworks in CDM Host Countries interact with international rules on carbon trading, and how the former can be enhanced to facilitate the implementation and financing of CDM projects. (author)
Cosmological models with running cosmological term and decaying dark matter
Szydlowski, Marek
2015-01-01
We are investigating dynamics of the generalized $\\Lambda$CDM model, which the $\\Lambda$ term is running with the cosmological time. We demonstrate that this model of $\\Lambda(t)$CDM cosmology can easily interpret in the interacting cosmology. Time, which is depended on $\\Lambda$ term, is emerging from the covariant theory of the scalar field $\\phi$ with the self-interacting potential $V(\\phi)$. On the example of the model $\\Lambda(t)=\\Lambda_{\\text{bare}}+\\frac{\\alpha^2}{t^2}$ we show the existence of a mechanism of the modification of the scaling law for energy density of dark matter: $\\rho_{\\text{dm}}\\propto a^{-3+\\delta(t)}$. We also present the idea of the testing $\\Lambda(t)$CDM model with dark energy and dark matter not as an isolated hypothesis but as integral part of the concordance cosmological model. At the $2\\sigma$ confidence level, we find $\\delta<0$, which is an evidence that the energy transfer from decaying dark matter is favored. This effect gives rise to lowering a mass of dark matter pa...
Confronting the Hubble diagram of gamma-ray bursts with Cardassian cosmology
Energy Technology Data Exchange (ETDEWEB)
Mosquera Cuesta, Herman J; Habib Dumet M; Furlanetto, Cristina, E-mail: hermanjc@cbpf.br, E-mail: hdumetm@cbpf.br, E-mail: crisf@cbpf.br [Instituto de Cosmologia, Relatividade e Astrofisica (ICRA-BR), Centro Brasileiro de Pesquisas Fisicas, Rua Dr Xavier Sigaud 150, Cep 22290-180, Urca, Rio de Janeiro, RJ (Brazil)
2008-07-15
We construct the Hubble diagram of gamma-ray bursts (GRBs) with redshifts reaching up to z{approx}6, by using five luminosity versus luminosity indicator relations calibrated with the Cardassian cosmology. This model has a major interesting feature: despite being matter dominated and flat, it can explain the present accelerated expansion of the universe. This is the first study of this class of models using high redshift GRBs. We have performed a {chi} squared statistical analysis of the GRBs calibrated with the Cardassian model, and also combined them with both the current cosmic microwave background and baryonic acoustic oscillation data. Our results show consistency between the current observational data and the model predictions; in particular, the best fit parameters obtained from that {chi}{sup 2} analysis are in agreement with those obtained from previous investigations. The influence of these best fit parameters on the redshift at which the universe would start to follow the Cardassian expansion, i.e., z{sub card}, and on both the redshift at which the universe supposedly had started to accelerate, i.e., z{sub acc}, and the age-redshift relation, H{sub 0}t{sub 0}, are also discussed. Our results also show that the universe, from the point of view of GRBs, had undergone a transition to acceleration at a redshift z Almost-Equal-To 0.2-0.7, which agrees with the type Ia supernovae results. One important point that we notice is that despite the statistical analysis being performed with a model that does not need any vacuum energy, we found that the results attained using this cosmological model are compatible with those obtained with the concordance cosmology ({Lambda}-CDM; CDM: cold dark matter), as far as GRBs are concerned. Hence, after confronting the Cardassian scenario with the GRB Hubble diagram, our main conclusion is that GRBs should indeed be considered a tool complementary to several other observational studies for doing precision cosmology.
Constraining the CDM spectrum normalization in flat dark energy cosmologies
Basilakos, S; Basilakos, Spyros
2006-01-01
We study the relation between the rms mass fluctuations on 8$h^{-1}$Mpc scales and $\\Omega_{\\rm m}$ using the recent clustering results of XMM-{\\it Newton} soft (0.5-2 keV) X-ray sources, which have a median redshift of $z\\sim 1.2$. The relation can be represented in the form $\\sigma_{8}=0.34 (\\pm 0.01) \\Omega_{\\rm m}^{-\\gamma}$ where $\\gamma\\equiv \\gamma(\\Omega_{\\rm m},w)$ and it is valid for all $w<-1/3$ models. By combining the X-ray clustering and SNIa data we find that the model which best reproduces the observational data is that with: $\\Omega_{\\rm m}\\simeq 0.26$, $w\\simeq -0.90$ and $\\sigma_{8}\\simeq 0.73$, which is in excellent agreement with the recent 3-year Wilkinson Microwave Anisotropy Probe results.
Integrating ecological restoration into CDM forestry projects
International Nuclear Information System (INIS)
Highlights: • Concerns and issues in sustainability of CDM forestry projects are reviewed. • Ecological restoration is suggested to be integrated in the CDM framework. • As an ecosystem supporting service, soil restoration on degraded land is of primary importance. • Regenerating forests naturally rather than through monoculture plantations is suggested. • Potential social impacts of ecological restoration are discussed. - Abstract: The Clean Development Mechanism (CDM) is proposed to reduce greenhouse gas emissions and promote sustainable development. CDM forestry projects should contribute to mitigation of climate change through afforestation and reforestation (A/R) activities on degraded land in developing countries. However, like other types of CDM projects, the forestry projects have encountered a number of concerns and critiques. Appropriate approaches and concrete aims to achieve long-term sustainability have been lacking, and reforms have therefore been called for. The aims of this paper are to examine the published information relevant to these concerns, and frame appropriate approaches for a more sustainable CDM. In this review, as a first step to tackle some of these issues, ecological restoration is suggested for integration into the CDM framework. Essentially, this involves the restoration of ecosystem supporting service (soil restoration), upon which forests regenerate naturally rather than establishing monoculture plantations. In this way, forestry projects would bring cost-effective opportunities for multiple ecosystem services. Potential approaches, necessary additions to the monitoring plans, and social impacts of ecological restoration in CDM projects are discussed
A study of regional CDM projects distribution in China
Institute of Scientific and Technical Information of China (English)
Liu Xutong; Liu Qingqian; Gu A'lun
2009-01-01
sector development, CDM market and information circulation aspects, suggestions are given to support CDM development in western areas by the "sector development guidance + CDM capability construction + market support" mode in this paper.
Montani, Giovanni
1. Historical picture. 1.1. The concept of universe through the centuries. 1.2. The XIX century knowledge. 1.3. Birth of scientific cosmology. 1.4. The genesis of the hot big bang model. 1.5. Guidelines to the literature -- 2. Fundamental tools. 2.1. Einstein equations. 2.2. Matter fields. 2.3. Hamiltonian formulation of the dynamics. 2.4. Synchronous reference system. 2.5. Tetradic formalism. 2.6. Gauge-like formulation of GR. 2.7. Singularity theorems. 2.8. Guidelines to the literature -- 3. The structure and dynamics of the isotropic universe. 3.1. The RW geometry. 3.2. The FRW cosmology. 3.3. Dissipative cosmologies. 3.4. Inhomogeneous fluctuations in the universe. 3.5. General relativistic perturbation theory. 3.6. The Lemaitre-Tolmann-Bondi spherical solution. 3.7. Guidelines to the literature -- 4. Features of the observed universe. 4.1. Current status: The concordance model. 4.2. The large-scale structure. 4.3. The acceleration of the universe. 4.4. The cosmic microwave background. 4.5. Guidelines to the literature -- 5. The theory of inflation. 5.1. The shortcomings of the standard cosmology. 5.2. The inflationary paradigm. 5.3. Presence of a self-interacting scalar field. 5.4. Inflationary dynamics. 5.5. Solution to the shortcomings of the standard cosmology. 5.6. General features. 5.7. Possible explanations for the present acceleration of the universe. 5.8. Guidelines to the literature -- 6. Inhomogeneous quasi-isotropic cosmologies. 6.1. Quasi-isotropic solution. 6.2. The presence of ultrarelativistic matter. 6.3. The role of a massless scalar field. 6.4. The role of an electromagnetic field. 6.5. Quasi-isotropic inflation. 6.6. Quasi-isotropic viscous solution. 6.7. Guidelines to the literature -- 7. Homogeneous universes. 7.1. Homogeneous cosmological models. 7.2. Kasner solution. 7.3. The dynamics of the Bianchi models. 7.4. Bianchi types VIII and IX models. 7.5. Dynamical systems approach. 7.6. Multidimensional homogeneous universes. 7.7. Guidelines
Extended Born-Infeld Dynamics and Cosmology
Novello, M; Werneck, L S; Romero, C A
2005-01-01
We introduce an extension of the Born-Infeld action for a scalar field and show that it can act as unifying-dark-matter, providing an explanation for both structure formation and the accelerated expansion of the universe. We investigate the cosmological dynamics of this theory in a particular case, referred as the "Milne-Born-Infeld" (MBI) Lagrangian. We show that this model, whose equation of state has effectively a single free parameter, is consistent with recent type Ia supernovae data, providing a fit as good as for the $\\Lambda$CDM model with the same number of degrees of freedom. Furthermore, this parameter is tightly constrained by current data, making the model easily testable with other observables. Contrary to previous candidates for unifying-dark-matter, the sound velocity of the MBI model is vanishing both close to the dark matter state as well as near the cosmological constant state. This could avoid the problems on the matter power spectrum that were present in previous adiabatic dark-matter/dar...
Dirian, Yves; Foffa, Stefano; Kunz, Martin; Maggiore, Michele; Pettorino, Valeria
2016-05-01
We present a comprehensive and updated comparison with cosmological observations of two non-local modifications of gravity previously introduced by our group, the so called RR and RT models. We implement the background evolution and the cosmological perturbations of the models in a modified Boltzmann code, using CLASS. We then test the non-local models against the Planck 2015 TT, TE, EE and Cosmic Microwave Background (CMB) lensing data, isotropic and anisotropic Baryonic Acoustic Oscillations (BAO) data, JLA supernovae, H0 measurements and growth rate data, and we perform Bayesian parameter estimation. We then compare the RR, RT and ΛCDM models, using the Savage-Dickey method. We find that the RT model and ΛCDM perform equally well, while the performance of the RR model with respect to ΛCDM depends on whether or not we include a prior on H0 based on local measurements.
A Consistent Approach to Falsifying Lambda-CDM with Rare Galaxy Clusters
Harrison, Ian
2013-01-01
We consider methods with which to answer the question "is any observed galaxy cluster too unusual for Lambda-CDM?" After emphasising that many previous attempts to answer this question have fallen foul of a statistical bias which causes them to overestimate the confidence levels to which Lambda-CDM can be ruled out, we outline a consistent approach to these rare clusters which allows the question to be answered. We explicitly separate the two procedures of first ranking clusters according to which appears 'most unusual' and secondly calculating the probability that such an unusual observation was made in a given cosmology. For the ranking procedure we define three properties of individual galaxy clusters, each of which are sensitive to changes in cluster populations arising from different modifications to the cosmological model. We use these properties to define the "equivalent mass at redshift zero" for a cluster - the mass of an equally unusual cluster today. This quantity is independent of the observationa...
Testing CCDM Cosmology with the Radiation Temperature-Redshift Relation
Baranov, I; Lima, J A S
2016-01-01
The standard $\\Lambda$CDM model can be mimicked at the background and perturbative levels (linear and non-linear) by a class of gravitationally induced particle production cosmology dubbed CCDM cosmology. However, the radiation component in the CCDM model follows a slightly different temperature-redshift $T(z)$-law which depends on an extra parameter, $\
Can the Clean Development Mechanism (CDM) deliver?
International Nuclear Information System (INIS)
The paper investigates whether the Clean Development Mechanism (CDM) under the Kyoto Protocol has played a significant role in the development of rural communities, specifically investigating uptake of small-scale renewable energy projects. The investigation involved an assessment of 500 registered small-scale CDM projects under the Kyoto Protocol in terms of their potential impact on the envisaged sustainable development goals for rural communities. Five case studies from the Indian subcontinent were also examined. The paper concludes that the CDM in its current state and design has typically failed to deliver the promised benefits with regard to development objectives in rural areas. Successful projects were found to have had good community involvement and such projects were typically managed by cooperative ventures rather than money making corporations. The paper puts forward a new framework for the assessment of such benefits in the hope that future projects can be better assessed in this regard. The key problem, however, remains on how to deal with the inherent contradiction between development and sustainability. - Research Highlights: → Role of CDM towards sustainable development of rural communities. → Assessment of 500 registered small-scale CDM projects. → CDM in its current state and design has typically failed to deliver. → A new framework for sustainable development assessment of small-scale CDM projects. → Inherent contradiction between development and sustainability.
Running cosmological constant with observational tests
Geng, Chao-Qiang; Lee, Chung-Chi; Zhang, Kaituo
2016-01-01
We investigate the running cosmological constant model with dark energy linearly proportional to the Hubble parameter, $\\Lambda = \\sigma H + \\Lambda_0$, in which the $\\Lambda$CDM limit is recovered by taking $\\sigma=0$. We derive the linear perturbation equations of gravity under the Friedmann-Lema\\"itre-Robertson-Walker cosmology, and show the power spectra of the CMB temperature and matter density distribution. By using the Markov chain Monte Carlo method, we fit the model to the current ob...
Nagai, D; Nagai, Daisuke; Kravtsov, Andrey V.
2003-01-01
Recently, high-resolution Chandra observations revealed the existence of very sharp features in the X-ray surface brightness and temperature maps of several clusters (Vikhlinin et. al., 2001). These features, called ``cold fronts'', are characterized by an increase in surface brightness by a factor >2 over 10-50 kpc, accompanied by a drop in temperature of a similar magnitude. The existence of such sharp gradients can be used to put interesting constraints on the physics of the intracluster medium (ICM), if their mechanism and longevity are well understood. Here, we present results of a search for cold fronts in high-resolution simulations of galaxy clusters in cold dark matter (CDM) models. We show that sharp gradients with properties similar to those of observed cold fronts naturally arise in cluster mergers when the shocks heat gas surrounding the merging sub-cluster, while its dense core remains relatively cold. The compression induced by supersonic motions and shock heating during the merger enhance the ...
Navarro, J F
1995-01-01
High resolution N-body simulations show that the density profiles of dark matter halos formed in the standard CDM cosmogony can be fit accurately by scaling a simple ``universal'' profile. Regardless of their mass, halos are nearly isothermal over a large range in radius, but significantly shallower than r^{-2} near the center and steeper than r^{-2} in the outer regions. The characteristic overdensity of a halo correlates strongly with halo mass in a manner consistent with the mass dependence of the epoch of halo formation. Matching the shape of the rotation curves of disk galaxies with this halo structure requires (i) disk mass-to-light ratios to increase systematically with luminosity, (ii) halo circular velocities to be systematically lower than the disk rotation speed, and (iii) that the masses of halos surrounding bright galaxies depend only weakly on galaxy luminosity. This offers an attractive explanation for the puzzling lack of correlation between luminosity and dynamics in observed samples of binar...
Comparison of Cluster Lensing Profiles with Lambda CDM Predictions
Broadhurst, Tom; Medezinski, Elinor; Oguri, Masamune; Rephaeli, Yoel
2008-01-01
We derive lens distortion and magnification profiles of four well known clusters observed with Subaru. Each cluster is very well fitted by the general form predicted for Cold Dark Matter (CDM) dominated halos, with good consistency found between the independent distortion and magnification measurements. The inferred level of mass concentration is surprisingly high, 8 = 10.39 \\pm 0.91), compared to the relatively shallow profiles predicted by the LCDM model, c_{vir} = 5.06 \\pm 1.10 (for =1.25\\times 10^{15} M_{\\odot}/h). This represents a 4\\sigma discrepancy, and includes the relatively modest effects of projection bias and profile evolution derived from N-body simulations, which oppose each other with little residual effect. In the context of CDM based cosmologies, this discrepancy implies some modification of the widely assumed spectrum of initial density perturbations, so clusters collapse earlier (z > 1) than predicted (z<0.5) when the Universe was correspondingly denser.
Scalar-tensor extension of the $\\Lambda$CDM model
Algoner, W C; Zimdahl, W
2016-01-01
We construct a cosmological scalar-tensor-theory model in which the Brans-Dicke type scalar $\\Phi$ enters the effective (Jordan-frame) Hubble rate as a simple modification of the Hubble rate of the $\\Lambda$CDM model. This allows us to quantify differences between the background dynamics of scalar-tensor theories and general relativity (GR) in a transparent and observationally testable manner in terms of one single parameter. Problems of the mapping of the scalar-field degrees of freedom on an effective fluid description in a GR context are discused. Data from supernovae, the differential age of old galaxies and baryon acoustic oscillations are shown to strongly limit potential deviations from the standard model.
Constraints on the $\\Lambda$CDM model with redshift tomography
Cai, Rong-Gen; Tang, Bo
2013-01-01
Recently released Planck data favor a lower value of the Hubble constant and a higher value of the fraction matter density in the standard $\\Lambda$CDM model, which are discrepant with some of the low-redshift measurements. Within the context of this cosmology, we examine the consistency of the estimated values for the Hubble constant and fraction matter density with redshift tomography. Using the SNe Ia, Hubble parameter, BAO and CMB data, which are divided into three bins, we find no statistical evidence for any tension in the three redshift bins, although there exists a 1.4$\\sigma$ deviation of the Hubble constant in the middle redshift from the one in the high redshift bin.
Cosmological dynamics of extended chameleons
Tamanini, Nicola
2016-01-01
We investigate the cosmological dynamics of the recently proposed extended chameleon models at both background and linear perturbation levels. Dynamical systems techniques are employed to fully characterize the evolution of the universe at the largest distances, while structure formation is analysed at sub-horizon scales within the quasi-static approximation. The late time dynamical transition from dark matter to dark energy domination can be well described by almost all extended chameleon models considered, with no deviations from $\\Lambda$CDM results at both background and perturbation levels. The results obtained in this work confirm the cosmological viability of extended chameleons as alternative dark energy models.
Zhao, Wen
2016-01-01
The foundation of modern cosmology relies on the so-called cosmological principle which states an homogeneous and isotropic distribution of matter in the universe on large scales. However, recent observations, such as the temperature anisotropy of the cosmic microwave background (CMB) radiation, the motion of galaxies in the universe, the polarization of quasars and the acceleration of the cosmic expansion, indicate preferred directions in the sky. If these directions have a cosmological origin, the cosmological principle would be violated, and modern cosmology should be reconsidered. In this paper, by considering the preferred axis in the CMB parity violation, we find that it coincides with the preferred axes in CMB quadrupole and CMB octopole, and they all align with the direction of the CMB kinematic dipole. In addition, the preferred directions in the velocity flows, quasar alignment, anisotropy of the cosmic acceleration, the handedness of spiral galaxies, and the angular distribution of the fine-structu...
Bimetric gravity is cosmologically viable
Directory of Open Access Journals (Sweden)
Yashar Akrami
2015-09-01
Full Text Available Bimetric theory describes gravitational interactions in the presence of an extra spin-2 field. Previous work has suggested that its cosmological solutions are generically plagued by instabilities. We show that by taking the Planck mass for the second metric, Mf, to be small, these instabilities can be pushed back to unobservably early times. In this limit, the theory approaches general relativity with an effective cosmological constant which is, remarkably, determined by the spin-2 interaction scale. This provides a late-time expansion history which is extremely close to ΛCDM, but with a technically-natural value for the cosmological constant. We find Mf should be no larger than the electroweak scale in order for cosmological perturbations to be stable by big-bang nucleosynthesis. We further show that in this limit the helicity-0 mode is no longer strongly-coupled at low energy scales.
China's CDM Policies and Their Development Implications: Major Concerns for CDM Implementation
Institute of Scientific and Technical Information of China (English)
Zhu Xianli; Pan Jiahua
2006-01-01
Most CDM (Clean Development Mechanism)opportunities exist in some large industrializing developing countries. For instance, China is estimated to take 48% of the world potential for CDM project activities. In reality, however, the share by China over the CDM projects registered and CDM projects in the pipeline is less than 10% as of Auguest 2005. This paper will examine the reasons behind, as reflected in China's CDM policies. Further investigation will be made into the use of these policies to boost the country's sustainable development, the sustainable development implications and effects of these policies. In addition, it is noted that incompatibility of some other Chinese laws and policies can be responsible for the low level and slow pace of CDM implementation in China and some suggestions are offered for promoting CDM project activities in China. There also exist barriers at the international level that impedes implementation of CDM project activities. A conclusion is drawn that CDM policies in a developing country like China aim mainly at promotion of sustainable development and to a lesser extent the generation of CERs.
Rich, James
2009-01-01
The book is aimed at astrophysics students and professional physicists who wish to understand the basics of cosmology and general relativity as well as the observational foundations of the LambdaCDM model of the Universe. The book provides a self-contained introduction to general relativity that is based on the homogeneity and isotropy of the local universe. The simplicity of this space allows general relativity to be presented in a very elementary manner while laying the foundation for the treatment of more complicated problems. The new edition presents the most recent observations, including those of CMB anisotropies by WMAP and of Baryon Acoustic Oscillations by SDSS. Future observational and theoretical challenges for the understanding of dark energy and dark matter are discussed. From 1st edition reviews: "The book provides a comprehensive and thorough explication of current cosmology at a level appropriate for a beginning graduate student or an advanced and motivated undergraduate. ... This is an extrem...
Gariazzo, Stefano
2016-01-01
In this Thesis I discuss several recent results obtained using the CMB spectra measured by Planck and several other cosmological probes. Extensions of the $\\Lambda$CDM model are studied, including the presence of an additional sterile neutrino (motivated by the short-baseline oscillation anomalies) and of a thermal axion. The degeneracies of the cosmological effects of these particles with the power spectrum of primordial perturbations are tested. We also show that the power spectrum of initial scalar perturbations can be degenerate with the presence of primordial non-Gaussianities, thus affecting the constraints on the non-Gaussianity parameter $f_{NL}$. Finally, an effective interaction between dark energy and dark matter is studied.
Full chip modelling of ICs under CDM stress
Sowariraj, Mary Sheela Bobby
2005-01-01
In this thesis, CDM ESD stress on the Integrated Circuits (IC) and the various factors which affect the robustness of an IC design against CDM stress is investigated. One of the main reasons for CDM failure are the voltage gradients set across the circuit during CDM stress. The IC being also the sou
Solomon, Adam R
2015-01-01
The accelerating expansion of the Universe poses a major challenge to our understanding of fundamental physics. One promising avenue is to modify general relativity and obtain a new description of the gravitational force. Because gravitation dominates the other forces mostly on large scales, cosmological probes provide an ideal testing ground for theories of gravity. In this thesis, we describe two complementary approaches to the problem of testing gravity using cosmology. In the first part, we discuss the cosmological solutions of massive gravity and its generalisation to a bimetric theory. These theories describe a graviton with a small mass, and can potentially explain the late-time acceleration in a technically-natural way. We describe these self-accelerating solutions and investigate the cosmological perturbations in depth, beginning with an investigation of their linear stability, followed by the construction of a method for solving these perturbations in the quasistatic limit. This allows the predictio...
The Imprint of Warm Dark Matter on the Cosmological 21-cm Signal
Sitwell, Michael; Ma, Yin-Zhe; Sigurdson, Kris
2013-01-01
We investigate the effects of warm dark matter (WDM) on the cosmic 21-cm signal. If dark matter exists as WDM instead of cold dark matter (CDM), its non-negligible velocities can inhibit the formation of low-mass halos that normally form first in CDM models, therefore delaying star-formation. The absence of early sources delays the build-up of UV and X-ray backgrounds that affect the 21-cm radiation signal produced by neutral hydrogen. With use of the 21CMFAST code, we demonstrate that the pre-reionization 21-cm signal can be changed significantly in WDM models with a free-streaming length equivalent to that of a thermal relic with mass mx of up to ~ 10-20 keV. In such a WDM cosmology, the 21-cm signal traces the growth of more massive halos, resulting in a delay of the 21-cm absorption signature and followed by accelerated X-ray heating. CDM models where astrophysical sources have a suppressed photon-production efficiency can delay the 21-cm signal as well, although its subsequent evolution is not as rapid a...
Exploring Bouncing Cosmologies with Cosmological Surveys
Cai, Yi-Fu
2014-01-01
In light of the recent observational data coming from the sky we have two significant directions in the field of theoretical cosmology recently. First, we are now able to make use of present observations, such as the Planck and BICEP2 data, to examine theoretical predictions from the standard inflationary $\\Lambda$CDM which were made decades of years ago. Second, we can search for new cosmological signatures as a way to explore physics beyond the standard cosmic paradigm. In particular, a subset of early universe models admit a nonsingular bouncing solution that attempts to address the issue of the big bang singularity. These models have achieved a series of considerable developments in recent years, in particular in their perturbative frameworks, which made brand-new predictions of cosmological signatures that could be visible in current and forthcoming observations. In this article we present two representative paradigms of very early universe physics. The first is the so-called new matter (or matter-ekpyro...
Confronting Lemaitre-Tolman-Bondi models with observational cosmology
Energy Technology Data Exchange (ETDEWEB)
Garcia-Bellido, Juan; Haugbolle, Troels, E-mail: juan.garciabellido@uam.es, E-mail: haugboel@phys.au.dk [Instituto de Fisica Teorica UAM-CSIC, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain)
2008-04-15
The possibility that we live in a special place in the universe, close to the centre of a large void, seems an appealing alternative to the prevailing interpretation of the acceleration of the universe in terms of a {Lambda}CDM model with a dominant dark energy component. In this paper we confront the asymptotically flat Lemaitre-Tolman-Bondi (LTB) models with a series of observations, from type Ia supernovae to cosmic microwave background and baryon acoustic oscillations data. We propose two concrete LTB models describing a local void in which the only arbitrary functions are the radial dependence of the matter density {Omega}{sub M} and the Hubble expansion rate H. We find that all observations can be accommodated within 1 sigma, for our models with four or five independent parameters. The best fit models have a {chi}{sup 2} very close to that of the {Lambda}CDM model. A general Fortran program for comparing LTB models with cosmological observations, that has been used to make the parameter scan in this paper, has been made public, and can be downloaded at http://www.phys.au.dk/{approx}haugboel/software.shtml together with IDL routines for creating the likelihood plots. We perform a simple Bayesian analysis and show that one cannot exclude the hypothesis that we live within a large local void of an otherwise Einstein-de Sitter model.
Confronting Lemaitre–Tolman–Bondi models with observational cosmology
International Nuclear Information System (INIS)
The possibility that we live in a special place in the universe, close to the centre of a large void, seems an appealing alternative to the prevailing interpretation of the acceleration of the universe in terms of a ΛCDM model with a dominant dark energy component. In this paper we confront the asymptotically flat Lemaitre–Tolman–Bondi (LTB) models with a series of observations, from type Ia supernovae to cosmic microwave background and baryon acoustic oscillations data. We propose two concrete LTB models describing a local void in which the only arbitrary functions are the radial dependence of the matter density ΩM and the Hubble expansion rate H. We find that all observations can be accommodated within 1 sigma, for our models with four or five independent parameters. The best fit models have a χ2 very close to that of the ΛCDM model. A general Fortran program for comparing LTB models with cosmological observations, that has been used to make the parameter scan in this paper, has been made public, and can be downloaded at http://www.phys.au.dk/~haugboel/software.shtml together with IDL routines for creating the likelihood plots. We perform a simple Bayesian analysis and show that one cannot exclude the hypothesis that we live within a large local void of an otherwise Einstein–de Sitter model
Cosmological implications of two types of baryon acoustic oscillation data
Hu, Yazhou; Li, Nan; Wang, Shuang
2015-01-01
Aims: We explore the cosmological implications of two types of baryon acoustic oscillation (BAO) data that are extracted by using the spherically averaged one-dimensional galaxy clustering (GC) statistics (hereafter BAO1) and the anisotropic two-dimensional GC statistics (hereafter BAO2), respectively. Methods: Firstly, making use of the BAO1 and the BAO2 data, as well as the SNLS3 type Ia supernovae sample and the Planck distance priors data, we constrain the parameter spaces of the $\\Lambda$CDM, the $w$CDM, and the Chevallier-Polarski-Linder (CPL) model. Then, we discuss the impacts of different BAO data on parameter estimation, equation of state $w$, figure of merit and deceleration-acceleration transition redshift. At last, we use various dark energy diagnosis, including Hubble diagram $H(z)$, deceleration diagram $q(z)$, statefinder hierarchy $\\{S^{(1)}_3, S^{(1)}_4\\}$, composite null diagnosic (CND) $\\{S^{(1)}_3, \\epsilon(z)\\}$ and $\\{S^{(1)}_4, \\epsilon(z)\\}$, to distinguish the differences between the...
Stable and unstable cosmological models in bimetric massive gravity
Könnig, Frank; Amendola, Luca; Motta, Mariele; Solomon, Adam R
2014-01-01
Nonlinear, ghost-free massive gravity has two tensor fields; when both are dynamical, the mass of the graviton can lead to cosmic acceleration that agrees with background data, even in the absence of a cosmological constant. Here the question of the stability of linear perturbations in this theory is examined. Instabilities are presented for several classes of models, and simple criteria for the cosmological stability of massive bigravity are derived. In this way, we identify a particular self-accelerating bigravity model, infinite-branch bigravity (IBB), which exhibits both viable background evolution and stable linear perturbations. We discuss the modified gravity parameters for IBB, which do not reduce to the standard $\\Lambda$CDM result at early times, and compute the combined likelihood from measured growth data and type Ia supernovae. IBB predicts a present matter density $\\Omega_{m0}=0.18$ and an equation of state $w(z)=-0.79+0.21z/(1+z)$. The growth rate of structure is well-approximated at late times...
Cosmological perturbations in mimetic matter model
Matsumoto, Jiro; Sushkov, Sergey V
2015-01-01
We investigate the cosmological evolution of mimetic matter model with arbitrary scalar potential. The cosmological reconstruction is explicitly done for different choices of potential. The cases that mimetic matter model shows the evolution as Cold Dark Matter(CDM), wCDM model, dark matter and dark energy with dynamical $Om(z)$ or phantom dark energy with phantom-non-phantom crossing are presented in detail. The cosmological perturbations for such evolution are studied in mimetic matter model. For instance, the evolution behavior of the matter density contrast which is different from usual one, i.e. $\\ddot \\delta + 2 H \\dot \\delta - \\kappa ^2 \\rho \\delta /2 = 0$ is investigated. The possibility of peculiar evolution of $\\delta$ in the model under consideration is shown. Special attention is paid to the behavior of matter density contrast near to future singularity where decay of perturbations may occur much earlier the singularity.
Srivastava, S. K.
2008-01-01
Here, cosmology is obtained from the variable gravitational constant $ G \\propto \\phi^{-2}$ with $ \\phi(x) $ being a scalar and its fluctuations around the ground state. The gravitational action contains Einstein-Hilbert like term with variable $ G $, kinetic energy and self-interaction potential for $ \\phi(x) $. Two phase transitions take place in this model. The first one takes place at the GUT (grand unified theory) scale $ \\sim 2.45 \\times 10^{14}{\\rm GeV} $, when the early universe exits...
Vacuum energy and the cosmological constant
Bass, Steven D
2015-01-01
The accelerating expansion of the Universe points to a small positive value for the cosmological constant or vacuum energy density. We discuss recent ideas that the cosmological constant plus LHC results might hint at critical phenomena near the Planck scale.
Cosmological constraints on variable warm dark matter
International Nuclear Information System (INIS)
Although ΛCDM model is very successful in many aspects, it has been seriously challenged. Recently, warm dark matter (WDM) remarkably rose as an alternative of cold dark matter (CDM). In the literature, many attempts have been made to determine the equation-of-state parameter (EoS) of WDM. However, in most of the previous works, it is usually assumed that the EoS of dark matter (DM) is constant (and usually the EoS of dark energy is also constant). Obviously, this assumption is fairly restrictive. It is more natural to assume a variable EoS for WDM (and dark energy). In the present work, we try to constrain the EoS of variable WDM with the current cosmological observations. We find that the best fits indicate WDM, while CDM is still consistent with the current observational data. However, ΛCDM is still better than WDM models from the viewpoint of goodness-of-fit. So, in order to distinguish WDM and CDM, the further observations on the small/galactic scale are required. On the other hand, in this work we also consider WDM whose EoS is constant, while the role of dark energy is played by various models. We find that the cosmological constraint on the constant EoS of WDM is fairly robust
Srivastava, S K
2008-01-01
Here, cosmology is obtained from the variable gravitational constant $ G \\propto \\phi^{-2}$ with $ \\phi(x) $ being a scalar and its fluctuations around the ground state. The gravitational action contains Einstein-Hilbert like term with variable $ G $, kinetic energy and self-interaction potential for $ \\phi(x) $. Two phase transitions take place in this model. The first one takes place at the GUT (grand unified theory) scale $ \\sim 2.45 \\times 10^{14}{\\rm GeV} $, when the early universe exits the inflationay phase and the second one at the electro-weak scale. Spontaneous symmetry breaking takes place around this scale As a consequence, variable $ G $ acquires constant value $G_N$ (the Newtonian gravitational constant).The standard model of cosmology is obtained in the post-second phase transition era. Interestingly, the dark matter and quintessence dark energy are created from the gravitational sector as a combined effect of the linear term of scalar curvature and $ \\phi(x) $ without using non-linear terms of...
Small scale problems of the $\\Lambda$CDM model: a short review
Del Popolo, Antonino
2016-01-01
The $\\Lambda$CDM model, or concordance cosmology, as it is often called, is a paradigm at its maturity. It has been checked against a large quantity of observations, and it passed almost all tests. The paradigm is clearly able to describe the universe at large scale, even if some issues remain open, like the cosmological constant problem, or the unexplained anomalies in the CMB. However, $\\Lambda$CDM clearly shows difficulty at small scales, that could be related to our scant understanding, from the nature of dark matter to that of gravity, or to the role of baryon physics, which is not well understood and implemented in simulation codes or in semi-analytic models. At this stage, it is of fundamental importance to understand if the problems encountered by the $\\Lambda$DCM model are a sign of its limits or a sign of our failures in getting the finer details right. In the present paper, we will review the small scale problems of the $\\Lambda$CDM model, we will discuss the proposed solutions and to what extent t...
Ryden, Barbara
2002-01-01
Introduction to Cosmology provides a rare combination of a solid foundation of the core physical concepts of cosmology and the most recent astronomical observations. The book is designed for advanced undergraduates or beginning graduate students and assumes no prior knowledge of general relativity. An emphasis is placed on developing the readers' physical insight rather than losing them with complex math. An approachable writing style and wealth of fresh and imaginative analogies from "everyday" physics are used to make the concepts of cosmology more accessible. The book is unique in that it not only includes recent major developments in cosmology, like the cosmological constant and accelerating universe, but also anticipates key developments expected in the next few years, such as detailed results on the cosmic microwave background.
Energy Technology Data Exchange (ETDEWEB)
Townsend, Paul K [Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA (United Kingdom); Wohlfarth, Mattias N R [Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA (United Kingdom)
2004-12-07
For gravity coupled to N scalar fields, with arbitrary potential V, it is shown that all flat (homogeneous and isotropic) cosmologies correspond to geodesics in an (N + 1)-dimensional 'augmented' target space of Lorentzian signature (1, N), timelike if V > 0, null if V = 0 and spacelike if V < 0. Accelerating cosmologies correspond to timelike geodesics that lie within an 'acceleration subcone' of the 'lightcone'. Non-flat (k = {+-}1) cosmologies are shown to evolve as projections of geodesic motion in a space of dimension N + 2, of signature (1, N + 1) for k = -1 and signature (2, N) for k = +1. This formalism is illustrated by cosmological solutions of models with an exponential potential, which are comprehensively analysed; the late-time behaviour for other potentials of current interest is deduced by comparison.
Hidden photon CDM search at Tokyo
Suzuki, Jun'ya; Horie, Tomoki; Minowa, Makoto
2015-01-01
We report on a search for hidden photon cold dark matter (HP CDM) using a novel technique with a dish antenna. We constructed two independent apparatus: one is aiming at the detection of the HP with a mass of $\\sim\\,\\rm{eV}$ which employs optical instruments, and the other is for a mass of $\\sim5\\times10^{-5}\\, \\rm{eV}$ utilizing a commercially available parabolic antenna facing on a plane reflector. From the result of the measurements, we found no evidence for the existence of HP CDM and set upper limits on the photon-HP mixing parameter $\\chi$.
Galaxy clustering, CMB and supernova data constraints on ϕCDM model with massive neutrinos
Directory of Open Access Journals (Sweden)
Yun Chen
2016-01-01
Full Text Available We investigate a scalar field dark energy model (i.e., ϕCDM model with massive neutrinos, where the scalar field possesses an inverse power-law potential, i.e., V(ϕ∝ϕ−α (α>0. We find that the sum of neutrino masses Σmν has significant impacts on the CMB temperature power spectrum and on the matter power spectrum. In addition, the parameter α also has slight impacts on the spectra. A joint sample, including CMB data from Planck 2013 and WMAP9, galaxy clustering data from WiggleZ and BOSS DR11, and JLA compilation of Type Ia supernova observations, is adopted to confine the parameters. Within the context of the ϕCDM model under consideration, the joint sample determines the cosmological parameters to high precision: the angular size of the sound horizon at recombination, the Thomson scattering optical depth due to reionization, the physical densities of baryons and cold dark matter, and the scalar spectral index are estimated to be θ⁎=(1.0415−0.0011+0.0012×10−2, τ=0.0914−0.0242+0.0266, Ωbh2=0.0222±0.0005, Ωch2=0.1177±0.0036, and ns=0.9644−0.0119+0.0118, respectively, at 95% confidence level (CL. It turns out that α<4.995 at 95% CL for the ϕCDM model. And yet, the ΛCDM scenario corresponding to α=0 is not ruled out at 95% CL. Moreover, we get Σmν<0.262 eV at 95% CL for the ϕCDM model, while the corresponding one for the ΛCDM model is Σmν<0.293 eV. The allowed scale of Σmν in the ϕCDM model is a bit smaller than that in the ΛCDM model. It is consistent with the qualitative analysis, which reveals that the increases of α and Σmν both can result in the suppression of the matter power spectrum. As a consequence, when α is larger, in order to avoid suppressing the matter power spectrum too much, the value of Σmν should be smaller.
Concordance cosmology without dark energy
Rácz, Gábor; Beck, Róbert; Szapudi, István; Csabai, István
2016-01-01
According to the general relativistic Birkhoff's theorem, spherically symmetric regions in an isotropic universe behave like mini-universes with their own cosmological parameters. We estimate local expansion rates for a large number of such regions, and use the volume-averaged increment of the scale parameter at each time step in an otherwise standard cosmological $N$-body simulation. The particle mass, corresponding to a coarse graining scale, is an adjustable parameter. This mean field approximation neglects tidal forces and boundary effects, but it is the first step towards a non-perturbative statistical backreaction calculation. We show that a volume-averaged simulation with the $\\Omega_m=1$ Einstein--de~Sitter setting in each region closely tracks the expansion and structure growth history of a $\\Lambda$CDM cosmology, and confirm the numerical results with analytic calculations as well. The very similar expansion history guarantees consistency with the concordance model and, due to the small but characte...
Cosmological stealths with nonconformal couplings
Ayón-Beato, Eloy; Terrero-Escalante, César A
2016-01-01
In this paper the existence of a stealth field during the evolution of our Universe is studied. With this aim, in the framework of the FRW cosmology, the case of non-conformal non-minimal coupling between a stealth scalar field and gravity is studied. It is shown that de Sitter's are the only backgrounds allowing for a stealth field fully depending on the spacetime coordinates. This way, such a field is not consistent with the present cosmological picture. If the stealth is homogeneous, then its dynamics is restricted by the underlying cosmological evolution. It is shown that homogeneous stealths can coexist with the kind of matter used to describe the matter content of our Universe according to the $\\Lambda$CDM model.
CDM. Is it a 'win-win' strategy for rural poverty alleviation in India?
Energy Technology Data Exchange (ETDEWEB)
Sirohi, Smita [Department of Dairy Economics, Statistics and Management, National Dairy Research Institute, Karnal, Haryana, 132001 (India)
2007-09-15
India is perceived to be one of the most attractive Non-Annex I countries for CDM project development. There are more than 350 projects in the CDM pipeline, largely in the areas of renewable energy, energy efficiency in industries and fossil fuel switching. This paper examines the socio-economic component of sustainable development commitments of the CDM projects to see if they can make any impact on rural poverty in India, since the goal of poverty alleviation lies at the core of the country's development priorities. The study concludes that CDM is not contributing to rural poverty alleviation to any notable extent. Nearly all the projects have a business orientation and are not directed to the development of rural poor. Even the renewable energy projects will have limited role in up-liftment of the masses below poverty line due to their weak resource base. For CDM to emerge as a 'win-win' strategy for poverty alleviation projects should be aimed at the rural communities and designed to accelerate agricultural growth in the rain-fed regions of the country.
Accelerating Universe with spacetime torsion but without dark matter and dark energy
Minkevich, A. V.
2009-01-01
It is shown that cosmological equations for homogeneous isotropic models deduced in the framework of the Poincar\\'e gauge theory of gravity by certain restrictions on indefinite parameters of gravitational Lagrangian take at asymptotics the same form as cosmological equations of general relativity theory for $\\Lambda CDM$-model. Terms related to dark matter and dark energy in cosmological equations of standard theory for $\\Lambda CDM$-model are connected in considered theory with the change o...
Determining Cosmology for a Nonlocal Realization of MOND
Kim, M; Sayeb, M; Tan, L; Woodard, R P; Xu, B
2016-01-01
We numerically determine the cosmological branch of the free function in a nonlocal metric-based modification of gravity which provides a relativistic generalization of Milgrom's Modified Newtonian Dynamics. Although we are not able to get exact agreement with $\\Lambda$CDM cosmology for the range $0 \\leq z < 0.0880$ the deviation is interesting in that it makes the current value of the Hubble parameter about 4.5% larger than in the $\\Lambda$CDM model. This may resolve the tension between inferences of $H_0$ which are based on data from large redshift and inferences based on Hubble plots.
Point mass Cosmological Black Holes
Firouzjaee, Javad T
2016-01-01
Real black holes in the universe are located in the expanding accelerating background which are called the cosmological black holes. Hence, it is necessary to model these black holes in the cosmological background where the dark energy is the dominant energy. In this paper, we argue that most of the dynamical cosmological black holes can be modeled by point mass cosmological black holes. Considering the de Sitter background for the accelerating universe, we present the point mass cosmological background in the cosmological de Sitter space time. Our work also includes the point mass black holes which have charge and angular momentum. We study the mass, horizons, redshift structure and geodesics properties for these black holes.
Stakeholder participation in CDM and new climate mitigation mechanisms: China CDM case study
DEFF Research Database (Denmark)
Dong, Yan; Olsen, Karen Holm
2015-01-01
Stakeholder participation is recognized as a key principle for effective climate governance. Climate mechanisms such as the Clean Development Mechanism (CDM), REDD +, and the Green Climate Fund (GCF) provide guidelines for local stakeholder consultation (LSC). However, little empirical research...... exists on how LSC is practised, and synergies between climate mechanisms are largely unexplored. This study explores how international LSC rules are practised at national and local levels. It aims to better shape future LSC in climate mechanisms by learning from the case of China. First, LSC policies...... in CDM, REDD +, and GCF are identified. Relevant rules in China’s local policies are analysed. To understand the interaction between CDM policies and China’s local LSC rules, a selection of Chinese CDM Projects Design Documents (PDDs) are analysed, providing an overall impression of the stakeholder...
Agarwal, Nishant; Khoury, Justin; Trodden, Mark
2009-01-01
We develop a fully covariant, well-posed 5D effective action for the 6D cascading gravity brane-world model, and use this to study cosmological solutions. We obtain this effective action through the 6D decoupling limit, in which an additional scalar degree mode, \\pi, called the brane-bending mode, determines the bulk-brane gravitational interaction. The 5D action obtained this way inherits from the sixth dimension an extra \\pi self-interaction kinetic term. We compute appropriate boundary terms, to supplement the 5D action, and hence derive fully covariant junction conditions and the 5D Einstein field equations. Using these, we derive the cosmological evolution induced on a 3-brane moving in a static bulk. We study the strong- and weak-coupling regimes analytically in this static ansatz, and perform a complete numerical analysis of our solution. Although the cascading model can generate an accelerating solution in which the \\pi field comes to dominate at late times, the presence of a critical singularity prev...
Cosmology with three interacting spin-2 fields
Lüben, Marvin; Akrami, Yashar; Amendola, Luca; Solomon, Adam R.
2016-08-01
Theories of massive gravity with one or two dynamical metrics generically lack stable and observationally viable cosmological solutions that are distinguishable from Λ cold dark matter (CDM). We consider an extension to trimetric gravity, with three interacting spin-2 fields which are not plagued by the Boulware-Deser ghost. We systematically explore every combination with two free parameters in search of background cosmologies that are competitive with Λ CDM . For each case we determine whether the expansion history satisfies viability criteria, and whether or not it contains beyond-Λ CDM phenomenology. Among the many models we consider, there are only three cases that seem to be both viable and distinguishable from standard cosmology. One of the models has only one free parameter and displays a crossing from above to below the phantom divide. The other two provide scaling behavior, although they contain future singularities that need to be studied in more detail. These models possess interesting features that make them compelling targets for a full comparison to observations of both cosmological expansion history and structure formation.
International Nuclear Information System (INIS)
The invention claims equipment for stabilizing the position of the front covers of the accelerator chamber in cyclic accelerators which significantly increases accelerator reliability. For stabilizing, it uses hydraulic cushions placed between the electromagnet pole pieces and the front chamber covers. The top and the bottom cushions are hydraulically connected. The cushions are disconnected and removed from the hydraulic line using valves. (J.P.)
CDM sustainable development impacts developed for the UNEP project 'CD4CDM'
Energy Technology Data Exchange (ETDEWEB)
Olhoff, Anne; Markandya, Anil; Halsnaes, Kirsten; Taylor, Tim
2004-07-01
The Clean Development Mechanism (CDM), an innovative cooperative mechanism under the Kyoto Protocol, is designed with the dual aim of assisting developing countries in achieving sustainable development (SD) and of assisting industrialised countries in achieving compliance with their greenhouse gas (GHG) emission reduction commitments. The SD dimension is not merely a requirement of the CDM; it should be seen as a main driver for developing country interest in participating in CDM projects. This is so, since apart from GHG emission reductions CDM projects will have a number of impacts in the host countries, including impacts on economic and social development and on the local environment. Furthermore, the selecting of the SD criteria and the assessment of the SD impacts are sovereign matters of the host countries in the current operationalisation of the Kyoto Protocol. National authorities can thus use the SD dimension to evaluate key linkages between national development goals and CDM projects, with the aim of selecting and designing CDM projects so that they create and maximise synergies with local development goals. (au)
Dirian, Yves; Kunz, Martin; Maggiore, Michele; Pettorino, Valeria
2016-01-01
We present a comprehensive and updated comparison with cosmological observations of two non-local modifications of gravity previously introduced by our group, the so called RR and RT models. We implement the background evolution and the cosmological perturbations of the models in a modified Boltzmann code, using CLASS. We then test the non-local models against the Planck 2015 TT, TE, EE and Cosmic Microwave Background (CMB) lensing data, isotropic and anisotropic Baryonic Acoustic Oscillations (BAO) data, JLA supernovae, $H_0$ measurements and growth rate data, and we perform Bayesian parameter estimation. We then compare the RR, RT and $\\Lambda$CDM models, using the Savage-Dickey method. We find that the RT model and $\\Lambda$CDM perform equally well, while the RR model is disfavored.
Revisiting Cosmological parameter estimation
Prasad, Jayanti
2014-01-01
Constraining theoretical models with measuring the parameters of those from cosmic microwave background (CMB) anisotropy data is one of the most active areas in cosmology. WMAP, Planck and other recent experiments have shown that the six parameters standard $\\Lambda$CDM cosmological model still best fits the data. Bayesian methods based on Markov-Chain Monte Carlo (MCMC) sampling have been playing leading role in parameter estimation from CMB data. In one of the recent studies \\cite{2012PhRvD..85l3008P} we have shown that particle swarm optimization (PSO) which is a population based search procedure can also be effectively used to find the cosmological parameters which are best fit to the WMAP seven year data. In the present work we show that PSO not only can find the best-fit point, it can also sample the parameter space quite effectively, to the extent that we can use the same analysis pipeline to process PSO sampled points which is used to process the points sampled by Markov Chains, and get consistent res...
The bispectrum of f(R) cosmologies
Energy Technology Data Exchange (ETDEWEB)
Gil-Marín, Héctor [Institute of Space Sciences (IEEC-CSIC), Faculty of Science, Campus UAB, Bellaterra 08193 (Spain); Schmidt, Fabian [Theoretical Astrophysics, California Institute of Technology, Mail Code 350-17, Pasadena, California 91125 (United States); Hu, Wayne [Kavli Institute for Cosmological Physics, Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637 (United States); Jimenez, Raul; Verde, Licia, E-mail: gil@ieec.uab.es, E-mail: fabians@caltech.edu, E-mail: whu@background.uchicago.edu, E-mail: raul.jimenez@icc.ub.edu, E-mail: liciaverde@icc.ub.edu [ICREA Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona (Spain)
2011-11-01
In this paper we analyze a suite of cosmological simulations of modified gravitational action f(R) models, where cosmic acceleration is induced by a scalar field that acts as a fifth force on all forms of matter. In particular, we focus on the bispectrum of the dark matter density field on mildly non-linear scales. For models with the same initial power spectrum, the dark matter bispectrum shows significant differences for cases where the final dark matter power spectrum also differs. Given the different dependence on bias of the galaxy power spectrum and bispectrum, bispectrum measurements can close the loophole of galaxy bias hiding differences in the power spectrum. Alternatively, changes in the initial power spectrum can also hide differences. By constructing ΛCDM models with very similar final non-linear power spectra, we show that the differences in the bispectrum are reduced (∼<4%) and are comparable with differences in the imperfectly matched power spectra. These results indicate that the bispectrum depends mainly on the power spectrum and less sensitively on the gravitational signatures of the f(R) model. This weak dependence of the matter bispectrum on gravity makes it useful for breaking degeneracies associated with galaxy bias, even for models beyond general relativity.
Strong Lensing Probabilities in a Cosmological Model with a Running Primordial Power Spectrum
Zhang, T J; Yang, Z L; He, X T; Zhang, Tong-Jie; Chen, Da-Ming; Yang, Zhi-Liang; He, Xiang-Tao
2004-01-01
The combination of the first-year Wilkinson Microwave Anisotropy Probe (WMAP) data with other finer scale cosmic microwave background (CMB) experiments (CBI and ACBAR) and two structure formation measurements (2dFGRS and Lyman $\\alpha$ forest) suggest a $\\Lambda$CDM cosmological model with a running spectral power index of primordial density fluctuations. Motivated by this new result on the index of primordial power spectrum, we present the first study on the predicted lensing probabilities of image separation in a spatially flat $\\Lambda$CDM model with a running spectral index (RSI-$\\Lambda$CDM model). It is shown that the RSI-$\\Lambda$CDM model suppress the predicted lensing probabilities on small splitting angles of less than about 4$^{''}$ compared with that of standard power-law $\\Lambda$CDM (PL-$\\Lambda$CDM) model.
Cosmology with a stiff matter era
Chavanis, Pierre-Henri
2015-11-01
We consider the possibility that the Universe is made of a dark fluid described by a quadratic equation of state P =K ρ2 , where ρ is the rest-mass density and K is a constant. The energy density ɛ =ρ c2+K ρ2 is the sum of two terms: a rest-mass term ρ c2 that mimics "dark matter" (P =0 ) and an internal energy term u =K ρ2=P that mimics a "stiff fluid" (P =ɛ ) in which the speed of sound is equal to the speed of light. In the early universe, the internal energy dominates and the dark fluid behaves as a stiff fluid (P ˜ɛ , ɛ ∝a-6). In the late universe, the rest-mass energy dominates and the dark fluid behaves as pressureless dark matter (P ≃0 , ɛ ∝a-3). We provide a simple analytical solution of the Friedmann equations for a universe undergoing a stiff matter era, a dark matter era, and a dark energy era due to the cosmological constant. This analytical solution generalizes the Einstein-de Sitter solution describing the dark matter era, and the Λ CDM model describing the dark matter era and the dark energy era. Historically, the possibility of a primordial stiff matter era first appeared in the cosmological model of Zel'dovich where the primordial universe is assumed to be made of a cold gas of baryons. A primordial stiff matter era also occurs in recent cosmological models where dark matter is made of relativistic self-gravitating Bose-Einstein condensates (BECs). When the internal energy of the dark fluid mimicking stiff matter is positive, the primordial universe is singular like in the standard big bang theory. It expands from an initial state with a vanishing scale factor and an infinite density. We consider the possibility that the internal energy of the dark fluid is negative (while, of course, its total energy density is positive), so that it mimics anti-stiff matter. This happens, for example, when the BECs have an attractive self-interaction with a negative scattering length. In that case, the primordial universe is nonsingular and
Cosmological effects of nonlinear electrodynamics
Energy Technology Data Exchange (ETDEWEB)
Novello, M [Instituto de Cosmologia Relatividade Astrofisica (ICRA-Brasil/CBPF), Rua Dr Xavier Sigaud, 150, CEP 22290-180, Rio de Janeiro (Brazil); Goulart, E [Instituto de Cosmologia Relatividade Astrofisica (ICRA-Brasil/CBPF), Rua Dr Xavier Sigaud, 150, CEP 22290-180, Rio de Janeiro (Brazil); Salim, J M [Instituto de Cosmologia Relatividade Astrofisica (ICRA-Brasil/CBPF), Rua Dr Xavier Sigaud, 150, CEP 22290-180, Rio de Janeiro (Brazil); Bergliaffa, S E Perez [Departamento de Fisica Teorica, Universidade do Estado do Rio de Janeiro, R. Sao Francisco Xavier, 524, Maracana, CEP 20559-900, Rio de Janeiro (Brazil)
2007-06-07
It will be shown that a given realization of nonlinear electrodynamics, used as a source of Einstein's equations, generates a cosmological model with interesting features, namely a phase of current cosmic acceleration, and the absence of an initial singularity, thus pointing to a way of solving two important problems in cosmology.
Dark matter and cosmic acceleration from Wesson's IMT
Israelit, Mark
2009-12-01
In the present work a procedure is build up, that allows obtaining dark matter (DM) and cosmic acceleration in our 4D universe embedded in a 5D manifold. Both, DM and the factor causing cosmic acceleration, as well ordinary matter are induced in the 4D space-time by a warped, but empty from matter, 5D bulk. The procedure is carried out in the framework of the Weyl-Dirac version (Israelit, Found Phys 35:1725, 2005; Israelit, Found Phys 35:1769, 2005) of Paul Wesson’s Induced Matter Theory (Wesson, Space-time matter, 1999) enriched by Rosen’s approach (Found Phys 12:213, 1982). Considering chaotically oriented Weyl vector fields, which exist in microscopic cells, we obtain cold dark matter (CDM) consisting of weylons, massive bosons having spin 1. Assuming homogeneity and isotropy at large scale we derive cosmological equations in which luminous matter, CDM and dark energy may be considered separately. Making in the given procedure use of present observational data one can develop a model of the Universe with conventional matter, DM and cosmic acceleration, induced by the 5D bulk.
The Shared Causal Pasts and Futures of Cosmological Events
Friedman, Andrew S; Gallicchio, Jason
2013-01-01
We derive criteria for whether two cosmological events can have a shared causal past or a shared causal future, assuming a Friedmann-Lemaitre-Robertson-Walker universe with best-fit \\Lambda CDM cosmological parameters from the Planck satellite. We further derive criteria for whether either cosmic event could have been in past causal contact with our own worldline since the time of the hot "big bang", which we take to be the end of early-universe inflation. We find that pairs of objects such as quasars on opposite sides of the sky with redshifts z >= 3.65 have no shared causal past with each other or with our past worldline. More complicated constraints apply if the objects are at different redshifts from each other or appear at some relative angle less than 180 degrees, as seen from Earth. We present examples of observed quasar pairs that satisfy all, some, or none of the criteria for past causal independence. Given dark energy and the recent accelerated expansion, our observable universe has a finite conform...
f(R,T,RμνTμν) gravity phenomenology and ΛCDM universe
International Nuclear Information System (INIS)
We propose general f(R,T,RμνTμν) theory as generalization of covariant Hořava-like gravity with dynamical Lorentz symmetry breaking. FRLW cosmological dynamics for several versions of such theory is considered. The reconstruction of the above action is explicitly done, including the numerical reconstruction for the occurrence of ΛCDM universe. De Sitter universe solutions in the presence of non-constant fluid are also presented. The problem of matter instability in f(R,T,RμνTμν) gravity is discussed
KiDS-450 : Cosmological parameter constraints from tomographic weak gravitational lensing
Hildebrandt, H.; Viola, M.; Heymans, C.; Joudaki, S.; Kuijken, K.; Blake, C.; Erben, T.; Joachimi, B.; Klaes, D.; Miller, L.; Morrison, C. B.; Nakajima, R.; Kleijn, G. Verdoes; Amon, A.; Choi, A.; Covone, G.; Jong, J. T. A. de; Dvornik, A.; Conti, I. Fenech; Grado, A.; Harnois-Déraps, J.; Herbonnet, R.; Hoekstra, H.; Köhlinger, F.; McFarland, J.; Mead, A.; Merten, J.; Napolitano, N.; Peacock, J. A.; Radovich, M.; Schneider, P.; Simon, P.; Valentijn, E. A.; Busch, J. L. van den; Uitert, E. van; Waerbeke, L. Van
2016-01-01
We present cosmological parameter constraints from a tomographic weak gravitational lensing analysis of ~450deg$^2$ of imaging data from the Kilo Degree Survey (KiDS). For a flat $\\Lambda$CDM cosmology with a prior on $H_0$ that encompasses the most recent direct measurements, we find $S_8\\equiv\\sig
Power law cosmology model comparison with CMB scale information
Tutusaus, Isaac; Blanchard, Alain; Dupays, Arnaud; Zolnierowski, Yves; Cohen-Tanugi, Johann; Ealet, Anne; Escoffier, Stéphanie; Fèvre, Olivier Le; Ilić, Stéphane; Piazza, Federico; Pisani, Alice; Plaszczynski, Stéphane; Sakr, Ziad; Salvatelli, Valentina; Schücker, Thomas; Tilquin, André; Virey, Jean-Marc
2016-01-01
Despite the ability of the cosmological concordance model ($\\Lambda$CDM) to describe the cosmological observations exceedingly well, power law expansion of the Universe scale radius has been proposed as an alternative framework. We examine here these models, analyzing their ability to fit cosmological data using robust model comparison criteria. Type Ia supernovae (SNIa), baryonic acoustic oscillations (BAO) and acoustic scale information from the cosmic microwave background (CMB) have been used. We find that SNIa data either alone or combined with BAO, can be well reproduced by both $\\Lambda$CDM and power law expansion models with $n \\sim 1.5$, while the constant expansion rate model ($n = 1$) is clearly disfavored. Allowing for some redshift evolution in the SNIa luminosity essentially removes any clear preference for a specific model. The CMB data is well known to provide the most stringent constraints on standard cosmological models, in particular through the position of the first peak of the temperature ...
Mavromatos, Nikolaos E
2007-01-01
In these Lectures I review possible constraints on particle physics models, obtained by means of combining the results of collider measurements with astrophysical data. I emphasize the theoretical-model dependence of these results. I discuss supersymmetric dark matter constraints at colliders (mainly LHC) in various theoretical contexts: the standard Cosmological-Constant-Cold-Dark-Matter (Lambda-CDM) model, (super)string-inspired ones and non-equilibrium relaxation dark energy models. I then investigate the capability of LHC measurements in asserting whether supersymmetric matter (if discovered) constitutes part, or all, of the astrophysical dark matter. I also discuss prospects for improving the constraints in future precision facilities, such as the International Linear Collider.
Cosmology with Superluminous Supernovae
Scovacricchi, Dario; Bacon, David; Sullivan, Mark; Prajs, Szymon
2015-01-01
We predict cosmological constraints for forthcoming surveys using Superluminous Supernovae (SLSNe) as standardisable candles. Due to their high peak luminosity, these events can be observed to high redshift (z~3), opening up new possibilities to probe the Universe in the deceleration epoch. We describe our methodology for creating mock Hubble diagrams for the Dark Energy Survey (DES), the "Search Using DECam for Superluminous Supernovae" (SUDSS) and a sample of SLSNe possible from the Large Synoptic Survey Telescope (LSST), exploring a range of standardisation values for SLSNe. We include uncertainties due to gravitational lensing and marginalise over possible uncertainties in the magnitude scale of the observations (e.g. uncertain absolute peak magnitude, calibration errors). We find that the addition of only ~100 SLSNe from SUDSS to 3800 Type Ia Supernovae (SNe Ia) from DES can improve the constraints on w and Omega_m by at least 20% (assuming a flat wCDM universe). Moreover, the combination of DES SNe Ia a...
Testing Fractional Action Cosmology
Shchigolev, V K
2015-01-01
The present work deals with a combined test of the so-called Fractional Action Cosmology (FAC) on the example of a specific model obtained by the author earlier. In this model, the effective cosmological term is proportional to the Hubble parameter squared through the so-called kinematic induction. The reason of studying this cosmological model could be explained by its ability to describe two periods of accelerated expansion, that is in agreement with the recent observations and the cosmological inflation paradigm. First of all, we put our model through the theoretical tests that gives a general conception of the influence of the model parameters on its behavior. Then, we obtain some restrictions on the principal parameters of the model, including the fractional index, by means of the observational data. Finally, the cosmography parameters and the observational data compared to the theoretical predictions are presented both analytically and graphically.
Testing fractional action cosmology
Shchigolev, V. K.
2016-08-01
The present work deals with a combined test of the so-called Fractional Action Cosmology (FAC) on the example of a specific model obtained by the author earlier. In this model, the effective cosmological term is proportional to the Hubble parameter squared through the so-called kinematic induction. The reason of studying this cosmological model could be explained by its ability to describe two periods of accelerated expansion, that is in agreement with the recent observations and the cosmological inflation paradigm. First of all, we put our model through the theoretical tests, which gives a general conception of the influence of the model parameters on its behavior. Then, we obtain some restrictions on the principal parameters of the model, including the fractional index, by means of the observational data. Finally, the cosmography parameters and the observational data compared to the theoretical predictions are presented both analytically and graphically.
Angular Distribution of Clustersin Skewed CDM Models
Borgani, S; Plionis, M
1994-01-01
We perform a detailed investigation of the statistical properties of the projected distribution of galaxy clusters obtained in Cold Dark Matter (CDM) models with both Gaussian and skewed primordial density fluctuations. We use N-body simulations to construct a set artificial Lick maps. An objective cluster--finding algorithm is used to identify clusters of different richness. For Gaussian models, the overall number of clusters is too small in the standard CDM case, but a model with higher normalisation fares much better; non--Gaussian models with negative skewness also fit faily well. We apply several statistical tests to compare real and simulated cluster samples, such as the 2-point correlation function, the minimal spanning tree construction, the multifractal analysis and the skewness of cell counts. The emerging picture is that Gaussian models, even with a higher normalization, are in trouble. Skew-positive models are also ruled out, while skew-negative models can reproduce the observed clustering of gala...
Viable singularity-free f(R) gravity without a cosmological constant.
Miranda, Vinícius; Jorás, Sergio E; Waga, Ioav; Quartin, Miguel
2009-06-01
Several authors have argued that self-consistent f(R) gravity models distinct from the cold dark matter model with a cosmological constant (LambdaCDM) are almost ruled out. Confronting such claims, we present a particular two-parameter f(R) model that (a) is cosmologically viable and distinguishable from LambdaCDM, (b) is compatible with the existence of relativistic stars, (c) is free of singularities of the Ricci scalar during the cosmological evolution, and (d) allows the addition of high-curvature corrections that could be relevant for inflation.
International Nuclear Information System (INIS)
In recent years different explanations are provided for both an inflation and a recent acceleration in the expansion of the universe. In this Letter we show that a model of physical interest is the modification of general relativity with a Gauss-Bonnet term coupled to a dynamical scalar-field as predicted by certain versions of string theory. This construction provides a model of evolving dark energy that naturally explains a dynamical relaxation of the vacuum energy (gravitationally repulsive pressure) to a small value (exponentially close to zero) after a sufficient number of e-folds. The model also leads to a small deviation from the w=-1 prediction of non-evolving dark energy
Energy Technology Data Exchange (ETDEWEB)
Neupane, Ishwaree P. [Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch (New Zealand) and Central Department of Physics, Tribhuvan University, Kirtipur, Kathmandu (Nepal)]. E-mail: ishwaree.neupane@cern.ch; Carter, Benedict M.N. [Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch (New Zealand)
2006-07-06
In recent years different explanations are provided for both an inflation and a recent acceleration in the expansion of the universe. In this Letter we show that a model hysical interest is the modification of general relativity with a Gauss-Bonnet term coupled to a dynamical scalar-field as predicted by certain versions of string theory. This construction provides a model of evolving dark energy that naturally explains a dynamical relaxation of the vacuum energy (gravitationally repulsive pressure) to a small value (exponentially close to zero) after a sufficient number of e-folds. The model also leads to a small deviation from the w=-1 prediction of non-evolving dark energy.
Townsend, P K; Townsend, Paul K.; Wohlfarth, Mattias N.R.
2004-01-01
For gravity coupled to N scalar fields with arbitrary potential V, it is shown that all flat (homogeneous and isotropic) cosmologies correspond to geodesics in an (N+1)-dimensional `extended target space' of Lorentzian signature (1,N), timelike if V>0 and spacelike if V<0. Accelerating cosmologies correspond to timelike geodesics that lie within an `acceleration subcone' of the `lightcone'. Non-flat (k=-1,+1) cosmologies are shown to evolve as projections of geodesic motion in a space of dimension N+2, of signature (1,N+1) for k=-1 and signature (2,N) for k=+1. We illustrate these results for various potentials of current interest, including exponential and inverse power potentials.
Tartaglia, Angelo
2015-01-01
Starting from some relevant facts concerning the behaviour of the universe over large scale and time span, the analogy between the geometric approach of General Relativ- ity and the classical description of an elastic strained material continuum is discussed. Extending the elastic deformation approach to four dimensions it is shown that the accelerated expansion of the universe is recovered. The strain field of space-time repro- duces properties similar to the ones ascribed to the dark energy currently called in to explain the accelerated expansion. The strain field in the primordial universe behaves as radiation, but asymptotically it reproduces the cosmological constant. Subjecting the theory to a number of cosmological tests confirms the soundness of the approach and gives an optimal value for the one parameter of the model, i.e. the bulk modulus of the space-time continuum. Finally various aspects of the Strained State Cosmology (SSC) are discussed and contrasted with some non-linear massive gravity theor...
Using supercluster geometry as a cosmological probe
Basilakos, S; Plionis, M
2001-01-01
We study the properties of superclusters detected in the Abell/ACO cluster catalogue. We identify the superclusters utilizing the `friend-of-friend' procedure, and then determine supercluster shapes by using the differential geometry approach. We find that the dominant supercluster morphological feature is filamentariness. We compare our Abell/ACO supercluster results with the corresponding ones generated from two different CDM cosmological models in order to investigate statistically which of the latter models best reproduces the observational results.
Cosmological perturbation theory in the synchronous and conformal newtonian gauges
Ma Chung Pei; Ma, Chung Pei; Bertschinger, Edmund
1995-01-01
This paper presents a systematic treatment of the linear theory of scalar gravitational perturbations in the synchronous gauge and the conformal Newtonian (or longitudinal) gauge. It differs from others in the literature in that we give, in both gauges, a complete discussion of all particle species that are relevant to any flat cold dark matter (CDM), hot dark matter (HDM), or CDM+HDM models (including a possible cosmological constant). The particles considered include CDM, baryons, photons, massless neutrinos, and massive neutrinos (an HDM candidate), where the CDM and baryons are treated as fluids while a detailed phase-space description is given to the photons and neutrinos. Particular care is applied to the massive neutrino component, which has been either ignored or approximated crudely in previous works. Isentropic initial conditions on super-horizon scales are derived. The coupled, linearized Boltzmann, Einstein and fluid equations that govern the evolution of the metric and density perturbations are t...
Cosmological dark energy effects from entanglement
International Nuclear Information System (INIS)
The thorny issue of relating information theory to cosmology is here addressed by assuming a possible connection between quantum entanglement measures and observable universe. In particular, we propose a cosmological toy model, where the equation of state of the cosmological fluid, which drives the today observed cosmic acceleration, can be inferred from quantum entanglement between different cosmological epochs. In such a way the dynamical dark energy results as byproduct of quantum entanglement.
Cosmological dark energy effects from entanglement
Energy Technology Data Exchange (ETDEWEB)
Capozziello, Salvatore, E-mail: capozziello@na.infn.it [Dipartimento di Fisica, Università di Napoli “Federico II”, Via Cinthia, 80126 Napoli (Italy); Istituto Nazionale di Fisica Nucleare (INFN), Sez. di Napoli, Via Cinthia, 80126 Napoli (Italy); Luongo, Orlando [Dipartimento di Fisica, Università di Napoli “Federico II”, Via Cinthia, 80126 Napoli (Italy); Istituto Nazionale di Fisica Nucleare (INFN), Sez. di Napoli, Via Cinthia, 80126 Napoli (Italy); Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de México (UNAM) (Mexico); Mancini, Stefano [Scuola di Scienze and Tecnologie, Università di Camerino, 62032 Camerino (Italy); Istituto Nazionale di Fisica Nucleare (INFN), Sez. di Perugia, Via Pascoli, 06123 Perugia (Italy)
2013-06-03
The thorny issue of relating information theory to cosmology is here addressed by assuming a possible connection between quantum entanglement measures and observable universe. In particular, we propose a cosmological toy model, where the equation of state of the cosmological fluid, which drives the today observed cosmic acceleration, can be inferred from quantum entanglement between different cosmological epochs. In such a way the dynamical dark energy results as byproduct of quantum entanglement.
K-mouflage gravity models that pass Solar System and cosmological constraints
Barreira, Alexandre; Clesse, Sebastien; Li, Baojiu; Valageas, Patrick
2015-01-01
We show that Solar System tests can place very strong constraints on K-mouflage models of gravity, which are coupled scalar field models with nontrivial kinetic terms that screen the fifth force in regions of large gravitational acceleration. In particular, the bounds on the anomalous perihelion of the Moon imposes stringent restrictions on the K-mouflage Lagrangian density, which can be met when the contributions of higher order operators in the static regime are sufficiently small. The bound on the rate of change of the gravitational strength in the Solar System constrains the coupling strength $\\beta$ to be smaller than $0.1$. These two bounds impose tighter constraints than the results from the Cassini satellite and Big Bang Nucleosynthesis. Despite the Solar System restrictions, we show that it is possible to construct viable models with interesting cosmological predictions. In particular, relative to $\\Lambda$-CDM, such models predict percent level deviations for the clustering of matter and the number ...
A Thousand Problems in Cosmology: Horizons
Bolotin, Yu L
2013-01-01
This is one chapter of the collection of problems in cosmology, in which we assemble the problems that concern one of the most distinctive features of general relativity and cosmology---the horizons. The first part gives an elementary introduction into the concept in the cosmological context, then we move to more formal exposition of the subject and consider first simple, and then composite models, such as $\\Lambda$CDM. The fourth section elevates the rigor one more step and explores the causal structure of different simple cosmological models in terms of conformal diagrams. The section on black holes relates the general scheme of constructing conformal diagrams for stationary black hole spacetimes. The consequent parts focus on more specific topics, such as the various problems regarding the Hubble sphere, inflation and holography. This version contains only formulations of 97 problems. The full collection, with solutions included, is available in the form of a wiki-based resource at http://universeinproblem...
Cosmology from start to finish.
Bennett, Charles L
2006-04-27
Cosmology is undergoing a revolution. With recent precise measurements of the cosmic microwave background radiation, large galaxy redshift surveys, better measurements of the expansion rate of the Universe and a host of other astrophysical observations, there is now a standard, highly constrained cosmological model. It is not a cosmology that was predicted. Unidentified dark particles dominate the matter content of our Universe, and mysteries surround the processes responsible for the accelerated expansion at its earliest moments (inflation?) and for its recent acceleration (dark energy?). New measurements must address the fundamental questions: what happened at the birth of the Universe, and what is its ultimate fate?
Reconstruction, thermodynamics and stability of the ΛCDM model in f(T,{ T }) gravity
Junior, Ednaldo L. B.; Rodrigues, Manuel E.; Salako, Ines G.; Houndjo, Mahouton J. S.
2016-06-01
We reconstruct the ΛCDM model for f(T,{ T }) theory, where T is the torsion scalar and { T } the trace of the energy-momentum tensor. The result shows that the action of ΛCDM is a combination of a linear term, a constant (-2{{Λ }}) and a nonlinear term given by the product \\sqrt{-T}{F}g[({T}1/3/16π G) (16π G{ T }+T+8{{Λ }})], with F g being a generic function. We show that to maintain conservation of the energy-momentum tensor, we should impose that {F}g[y] must be linear on the trace { T }. This reconstruction decays in f (T) theory for {F}g\\equiv Q, with Q a constant. Our reconstruction describes the cosmological eras to the present time. The model present stability within the geometric and matter perturbations for the choice {F}g=y, where y=({T}1/3/16π G)(16π G{ T }+T+8{{Λ }}), except for the geometric part in the de Sitter model. We impose the first and second laws of thermodynamics to ΛCDM and find the condition where they are satisfied, that is, {T}A,{G}{{eff}}\\gt 0, however where this is not possible in the cases that we choose, this leads to a breakdown of positive entropy and Misner–Sharp energy.
The distinctions between {Lambda}CDM and f(T) gravity according to Noether symmetry
Energy Technology Data Exchange (ETDEWEB)
Dong, Han; Wang, Jiaxin [Nankai University, Department of physics, Tianjin (China); Meng, Xinhe [Nankai University, Department of physics, Tianjin (China); CAS, Kavli Institute of Theoretical Physics China, Beijing (China)
2013-08-15
Noether's theory offers us a useful tool to research the conserved quantities and symmetries of the modified gravity theories, among which the f(T) theory, a generally modified teleparallel gravity, has been proposed to account for the dark energy phenomena. By the Noether symmetry approach, we investigate the power-law, exponential and polynomial forms of f(T) theories. All forms of f(T) concerned in this work possess the time translational symmetry, which is related with energy condition or Hamilton constraint. In addition, we find that the performances of the power-law and exponential forms are not pleasing. It is rational adding a linear term T to T {sup n} as the most efficient amendment to resemble the teleparallel gravity or General Relativity on small scales, i.e., the scale of the solar system. The corresponding Noether symmetry indicates that only time translational symmetry remains. Through numerically calculations and observational data-sets constraining, the optimal form {alpha}T+ {beta}T {sup -1} is obtained, whose cosmological solution resembles the standard {Lambda}CDM best with lightly reduced cosmic age which can be alleviated by introducing another T {sup m} term. More important is that we find the significant differences between {Lambda}CDM and f(T) gravity. The {Lambda}CDM model has also two additional symmetries and corresponding positive conserved quantities, except the two negative conserved quantities. (orig.)
Some Inflationary Einstein-Aether Cosmologies
Barrow, John D
2012-01-01
We show how to derive several families of accelerating universe solutions to an Einstein-Aether gravity theory. These solutions provide possible descriptions of inflationary behaviour in the early universe and late-time cosmological acceleration.
Cosmological test with the QSO Hubble diagram
López-Corredoira, M.; Melia, F.; Lusso, E.; Risaliti, G.
2016-03-01
A Hubble diagram (HD) has recently been constructed in the redshift range 0 ≲ z ≲ 6.5 using a nonlinear relation between the ultraviolet (UV) and X-ray luminosities of quasi stellar objects (QSOs). The Type Ia Supernovae (SN) HD has already provided a high-precision test of cosmological models, but the fact that the QSO distribution extends well beyond the supernova range (z ≲ 1.8), in principle provides us with an important complementary diagnostic whose significantly greater leverage in z can impose tighter constraints on the distance versus redshift relationship. In this paper, we therefore perform an independent test of nine different cosmological models, among which six are expanding, while three are static. Many of these are disfavored by other kinds of observations (including the aforementioned Type Ia SNe). We wish to examine whether the QSO HD confirms or rejects these earlier conclusions. We find that four of these models (Einstein-de Sitter, the Milne universe, the static universe with simple tired light and the static universe with plasma tired light) are excluded at the > 99% C.L. The quasi-steady state model is excluded at > 95% C.L. The remaining four models (ΛCDM/wCDM, the Rh = ct universe, the Friedmann open universe and a static universe with a linear Hubble law) all pass the test. However, only ΛCDM/wCDM and Rh = ct also pass the Alcock-Paczyński (AP) test. The optimized parameters in ΛCDM/wCDM are Ωm = 0.20-0.20+0.24 and wde = -1.2-∞+1.6 (the dark energy equation-of-state). Combined with the AP test, these values become Ωm = 0.38-0.19+0.20 and wde = -0.28-0.40+0.52. But whereas this optimization of parameters in ΛCDM/wCDM creates some tension with their concordance values, the Rh = ct universe has the advantage of fitting the QSO and AP data without any free parameters.
Faint dwarfs as a test of DM models: WDM vs. CDM
Governato, Fabio; Pontzen, Andrew; Loebman, Sarah; Reed, Darren; Brooks, Alyson M; Behroozi, Peter; Christensen, Charlotte; Madau, Piero; Mayer, Lucio; Shen, Sijing; Walker, Matthew; Quinn, Thomas; Wadsley, James
2014-01-01
We use high resolution Hydro$+$N-Body cosmological simulations to compare the assembly and evolution of a small field dwarf (stellar mass ~ 10$^{6-7}$ M$\\odot$, total mass 10$^{10}$ M$\\odot$ in $\\Lambda$ dominated CDM and 2keV WDM cosmologies. We find that star formation (SF) in the WDM model is reduced and delayed by 1-2 Gyr relative to the CDM model, independently of the details of SF and feedback. Independent of the DM model, but proportionally to the SF efficiency, gas outflows lower the central mass density through `dynamical heating', such that all realizations have circular velocities $<$ 20kms at 500$~$pc, in agreement with local kinematic constraints. As a result of dynamical heating, older stars are less centrally concentrated than younger stars, similar to stellar population gradients observed in nearby dwarf galaxies. We translate our simulations into artificial color-magnitude diagrams and star formation histories in order to directly compare to available observations. The simulated galaxies f...
Institute of Scientific and Technical Information of China (English)
曾学敏
2006-01-01
@@ 实施清洁发展机制(CDM)项目,在我国已掀起热潮,截止4月上旬,已有25个CDM项目获国家发改委批准,报联合国CDM执行理事会(EB)批准的项目已有7个,减排CO2当量3亿吨,交易额达20多亿美元.
Cosmological consequences of an adiabatic matter creation process
Nunes, Rafael C
2016-01-01
In this paper we investigate the cosmological consequences of a continuous matter creation associated with the production of particles by the gravitational field acting on the quantum vacuum. To illustrate this, three phenomenological models are considered. An equivalent scalar field description is presented for each models. The effects on the cosmic microwave background power spectrum are analyzed for the first time in the context of adiabatic matter creation cosmology. Further, we introduce a model independent treatment, $Om$, which depends only on the Hubble expansion rate and the cosmological redshift to distinguish any cosmological model from $\\Lambda$CDM by providing a null test for the cosmological constant, meaning that, for any two redshifts $z_1$, $z_2$, $Om (z)$ is same, i.e. $Om (z_1)- Om (z_2)= 0$. Also, this diagnostic can differentiate between several cosmological models by indicating their quintessential/ phantom behavior without knowing the accurate value of the matter density, and the presen...
Co-benefits of CDM projects and policy implications
Sun, Qie; Xu, Bo; Wennersten, Ronald; Brandt, Nils
2010-01-01
This paper aims to study the co-benefits of clean development mechanism (CDM) projects, and further to discuss the policy of its implications. It has been found that many energy-related climate change mitigation (CCM) activities, including CDM projects, are able to produce a significant amount of co-benefits, while the policy implications have been limited. Through co-benefits assessment of Chinese CDM projects, it can be concluded that: (1) there are uncertainties relating to co-benefits ass...
Cosmology with decaying cosmological constant -- exact solutions and model testing
Szydlowski, Marek
2015-01-01
We study dynamics of $\\Lambda(t)$ cosmological models which are a natural generalization of the standard cosmological model (the $\\Lambda$CDM model). We consider a class of models: the ones with a prescribed form of $\\Lambda(t)=\\Lambda_{\\text{bare}}+\\frac{\\alpha^2}{t^2}$. This type of a $\\Lambda(t)$ parametrization is motivated by different cosmological approaches. To guarantee the covariance principle in general relativity we interpreted $\\Lambda(t)$ relation as $\\Lambda(\\phi(t))$, where $\\phi(t)$ is a scalar field with a self-interacting potential $V(\\phi)$. For the $\\Lambda(t)$ cosmology with a prescribed form of $\\Lambda(t)$ we have found the exact solution in the form of Bessel functions. We have also constrained the model parameters for this class of models using the astronomical data such as SNIa data, BAO, CMB, measurements of $H(z)$ and the Alcock-Paczy{\\'n}ski test. In this context we formulate a simple criterion of variability of $\\Lambda$ with respect to $t$ in terms of variability of the jerk or ...
Energy Technology Data Exchange (ETDEWEB)
NONE
2012-11-01
The Swedish Energy Agency is responsible for the Swedish government program for the Clean Development Mechanism (CDM) and Joint Implementation (JI). CDM and JI is the Kyoto Protocol's two project-based flexible mechanisms. This program focuses on participation in individual CDM- and JI-projects and on participation in multilateral CDM- and JI- funds. In the report the Swedish Energy Agency, on behalf of the Government, presents a proposal for developed reporting for the CDM- and JI-program. Furthermore, issues related to how CDM and JI can assist in meeting the Swedish climate objective by 2020 are discussed. Also, the role for potential new flexible mechanisms under UN Climate Convention is mentioned.
The HII Galaxy Hubble Diagram Strongly Favors $R_{\\rm h}=ct$ over $\\Lambda$CDM
Wei, Jun-Jie; Melia, Fulvio
2016-01-01
We continue to build support for the proposal to use HII galaxies (HIIGx) and giant extragalactic HII regions (GEHR) as standard candles to construct the Hubble diagram at redshifts beyond the current reach of Type Ia supernovae. Using a sample of 25 high-redshift HIIGx, 107 local HIIGx, and 24 GEHR, we confirm that the correlation between the emission-line luminosity and ionized-gas velocity dispersion is a viable luminosity indicator, and use it to test and compare the standard model $\\Lambda$CDM and the $R_{\\rm h}=ct$ Universe by optimizing the parameters in each cosmology using a maximization of the likelihood function. For the flat $\\Lambda$CDM model, the best fit is obtained with $\\Omega_{\\rm m}= 0.40_{-0.09}^{+0.09}$. However, statistical tools, such as the Akaike (AIC), Kullback (KIC) and Bayes (BIC) Information Criteria favor $R_{\\rm h}=ct$ over the standard model with a likelihood of $\\approx 94.8\\%-98.8\\%$ versus only $\\approx 1.2\\%-5.2\\%$. For $w$CDM (the version of $\\Lambda$CDM with a dark-energy...
COSMIC EMULATION: THE CONCENTRATION-MASS RELATION FOR wCDM UNIVERSES
Energy Technology Data Exchange (ETDEWEB)
Kwan, Juliana; Bhattacharya, Suman; Heitmann, Katrin; Habib, Salman [High Energy Physics Division, Argonne National Laboratory, Lemont, IL 60439 (United States)
2013-05-10
The concentration-mass relation for dark matter-dominated halos is one of the essential results expected from a theory of structure formation. We present a simple prediction scheme, a cosmic emulator, for the concentration-mass (c-M) relation as a function of cosmological parameters for wCDM models. The emulator is constructed from 37 individual models, with three nested N-body gravity-only simulations carried out for each model. The mass range covered by the emulator is 2 Multiplication-Sign 10{sup 12} M{sub Sun} < M < 10{sup 15} M{sub Sun} with a corresponding redshift range of z = 0-1. Over this range of mass and redshift, as well as the variation of cosmological parameters studied, the mean halo concentration varies from c {approx} 2 to c {approx} 8. The distribution of the concentration at fixed mass is Gaussian with a standard deviation of one-third of the mean value, almost independent of cosmology, mass, and redshift over the ranges probed by the simulations. We compare results from the emulator with previously derived heuristic analytic fits for the c-M relation, finding that they underestimate the halo concentration at high masses. Using the emulator to investigate the cosmology dependence of the c-M relation over the currently allowable range of values, we find-not surprisingly-that {sigma}{sub 8} and {omega}{sub m} influence it considerably, but also that the dark energy equation-of-state parameter w has a substantial effect. In general, the concentration of lower-mass halos is more sensitive to changes in cosmological parameters as compared to cluster mass halos. The c-M emulator is publicly available from http://www.hep.anl.gov/cosmology/CosmicEmu.
Ellman, R
2000-01-01
Recently it has become possible to determine the distance to Type Ia supernovae by redshift-independent means. Those new distance determinations exceed the Hubble distance by 10 - 15%. The explanation others propose is that an "antigravity effect" is accelerating the universe' expansion, which had hitherto been thought to be slowing down because of gravitation. That has led to their proposing reinstatement of Einstein's "cosmological constant", a term in his equations introduced to account for gravitation not promptly collapsing the universe and which he disavowed upon Hubble's discovery of the expansion of the universe. And that has further led to their proposing some form of the Ancients' fifth essence, quintessence [the first four being earth, air, fire and water], to account for the "antigravity effect". Any "antigravity effect", regardless of its cause, would have the effect of counteracting ordinary gravitation. Inasmuch as one of the major current problems in cosmology is to identify more gravitation t...
Can we distinguish early dark energy from a cosmological constant?
Shi, Difu; Baugh, Carlton M.
2016-07-01
Early dark energy (EDE) models are a class of quintessence dark energy with a dynamically evolving scalar field which display a small but non-negligible amount of dark energy at the epoch of matter-radiation equality. Compared with a cosmological constant, the presence of dark energy at early times changes the cosmic expansion history and consequently the shape of the linear theory power spectrum and potentially other observables. We constrain the cosmological parameters in the EDE cosmology using recent measurements of the cosmic microwave background and baryon acoustic oscillations. The best-fitting models favour no EDE; here we consider extreme examples which are in mild tension with current observations in order to explore the observational consequences of a maximally allowed amount of EDE. We study the non-linear evolution of cosmic structure in EDE cosmologies using large-volume N-body simulations. Many large-scale structure statistics are found to be very similar between the Λ cold dark matter (ΛCDM) and EDE models. We find that EDE cosmologies predict fewer massive haloes in comparison to ΛCDM, particularly at high redshifts. The most promising way to distinguish EDE from ΛCDM is to measure the power spectrum on large scales, where differences of up to 15 per cent are expected.
COSMOLOGY WITH PHOTOMETRICALLY CLASSIFIED TYPE Ia SUPERNOVAE FROM THE SDSS-II SUPERNOVA SURVEY
Energy Technology Data Exchange (ETDEWEB)
Campbell, Heather; D' Andrea, Chris B; Nichol, Robert C.; Smith, Mathew; Lampeitl, Hubert [Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, PO1 3FX (United Kingdom); Sako, Masao [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States); Olmstead, Matthew D.; Brown, Peter; Dawson, Kyle S. [Department of Physics and Astronomy, University of Utah, 115 South 1400 East 201, Salt Lake City, UT 84112 (United States); Bassett, Bruce [Mathematics Department, University of Cape Town, Rondebosch, Cape Town (South Africa); Biswas, Rahul; Kuhlmann, Steve [Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL 60439 (United States); Cinabro, David [Department of Physics and Astronomy, Wayne State University, Detroit, MI 48126 (United States); Dilday, Ben [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Dr., Suite 102, Goleta, CA 93117 (United States); Foley, Ryan J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Frieman, Joshua A. [Department of Astronomy and Astrophysics, The University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Garnavich, Peter [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Hlozek, Renee [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Jha, Saurabh W. [Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, NJ 08854 (United States); Kunz, Martin, E-mail: Heather.Campbell@port.ac.uk [African Institute for Mathematical Sciences, Muizenberg, 7945, Cape Town (South Africa); and others
2013-02-15
We present the cosmological analysis of 752 photometrically classified Type Ia Supernovae (SNe Ia) obtained from the full Sloan Digital Sky Survey II (SDSS-II) Supernova (SN) Survey, supplemented with host-galaxy spectroscopy from the SDSS-III Baryon Oscillation Spectroscopic Survey. Our photometric-classification method is based on the SN classification technique of Sako et al., aided by host-galaxy redshifts (0.05 < z < 0.55). SuperNova ANAlysis simulations of our methodology estimate that we have an SN Ia classification efficiency of 70.8%, with only 3.9% contamination from core-collapse (non-Ia) SNe. We demonstrate that this level of contamination has no effect on our cosmological constraints. We quantify and correct for our selection effects (e.g., Malmquist bias) using simulations. When fitting to a flat {Lambda}CDM cosmological model, we find that our photometric sample alone gives {Omega} {sub m} = 0.24{sup +0.07} {sub -0.05} (statistical errors only). If we relax the constraint on flatness, then our sample provides competitive joint statistical constraints on {Omega} {sub m} and {Omega}{sub {Lambda}}, comparable to those derived from the spectroscopically confirmed Three-year Supernova Legacy Survey (SNLS3). Using only our data, the statistics-only result favors an accelerating universe at 99.96% confidence. Assuming a constant wCDM cosmological model, and combining with H {sub 0}, cosmic microwave background, and luminous red galaxy data, we obtain w = -0.96{sup +0.10} {sub -0.10}, {Omega} {sub m} = 0.29{sup +0.02} {sub -0.02}, and {Omega} {sub k} = 0.00{sup +0.03} {sub -0.02} (statistical errors only), which is competitive with similar spectroscopically confirmed SNe Ia analyses. Overall this comparison is reassuring, considering the lower redshift leverage of the SDSS-II SN sample (z < 0.55) and the lack of spectroscopic confirmation used herein. These results demonstrate the potential of photometrically classified SN Ia samples in improving
Determination of the cosmological parameters and the nature of dark energy
International Nuclear Information System (INIS)
The measured properties of the dark energy component being consistent with a Cosmological Constant, Λ, this cosmological standard model is referred to as the Λ-Cold-Dark-Matter (ΛCDM) model. Despite its overall success, this model suffers from various problems. The existence of a Cosmological Constant raises fundamental questions. Attempts to describe it as the energy contribution from the vacuum as following from Quantum Field Theory failed quantitatively. In consequence, a large number of alternative models have been developed to describe the dark energy component: modified gravity, additional dimensions, Quintessence models. Also, astrophysical effects have been considered to mimic an accelerated expansion. The basics of the ΛCDM model and the various attempts of explaining dark energy are outlined in this thesis. Another major problem of the model comes from the dependencies of the fit results on a number of a priori assumptions and parameterization effects. Today, combined analyses of the various cosmological probes are performed to extract the parameters of the model. Due to a wrong model assumption or a bad parameterization of the real physics, one might end up measuring with high precision something which is not there. We show, that indeed due to the high precision of modern cosmological measurements, purely kinematic approaches to distance measurements no longer yield valid fit results except for accidental special cases, and that a fit of the exact (integral) redshift-distance relation is necessary. The main results of this work concern the use of the CPL parameterization of dark energy when coping with the dynamics of tracker solutions of Quintessence models, and the risk of introducing biases on the parameters due to the possibly prohibited extrapolation to arbitrary high redshifts of the SN type Ia magnitude calibration relation, which is obtained in the low-redshift regime. Whereas the risks of applying CPL shows up to be small for a wide range of
DGP cosmological model with generalized Ricci dark energy
Energy Technology Data Exchange (ETDEWEB)
Aguilera, Yeremy [Universidad de Santiago, Departamento de Matematicas y Ciencia de la Computacion, Santiago (Chile); Avelino, Arturo [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States); Cruz, Norman [Universidad de Santiago, Departamento de Fisica, Facultad de Ciencia, Santiago (Chile); Lepe, Samuel [Pontificia Universidad Catolica de Valparaiso, Facultad de Ciencias, Instituto de Fisica, Valparaiso (Chile); Pena, Francisco [Universidad de La Frontera, Departamento de Ciencias Fisicas, Facultad de Ingenieria y Ciencias, Temuco (Chile)
2014-11-15
The brane-world model proposed by Dvali, Gabadadze and Porrati (DGP) leads to an accelerated universe without cosmological constant or other form of dark energy for the positive branch (element of = +1). For the negative branch (element of = -1) we have investigated the behavior of a model with an holographic Ricci-like dark energy and dark matter, where the IR cutoff takes the form αH{sup 2} + βH, H being the Hubble parameter and α, β positive constants of the model. We perform an analytical study of the model in the late-time dark energy dominated epoch, where we obtain a solution for r{sub c}H(z), where r{sub c} is the leakage scale of gravity into the bulk, and conditions for the negative branch on the holographic parameters α and β, in order to hold the conditions of weak energy and accelerated universe. On the other hand, we compare the model versus the late-time cosmological data using the latest type Ia supernova sample of the Joint Light-curve Analysis (JLA), in order to constrain the holographic parameters in the negative branch, as well as r{sub c}H{sub 0} in the positive branch, where H{sub 0} is the Hubble constant. We find that the model has a good fit to the data and that the most likely values for (r{sub c}H{sub 0}, α, β) lie in the permitted region found from an analytical solution in a dark energy dominated universe. We give a justification to use a holographic cutoff in 4D for the dark energy in the 5-dimensional DGP model. Finally, using the Bayesian Information Criterion we find that this model is disfavored compared with the flat ΛCDM model. (orig.)
Supernovae as cosmological probes
Nielsen, Jeppe Trost
2015-01-01
The cosmological standard model at present is widely accepted as containing mainly things we do not understand. In particular the appearance of a Cosmological Constant, or dark energy, is puzzling. This was first inferred from the Hubble diagram of a low number of Type Ia supernovae, and later corroborated by complementary cosmological probes. Today, a much larger collection of supernovae is available, and here I perform a rigorous statistical analysis of this dataset. Taking into account how the supernovae are calibrated to be standard candles, we run into some subtleties in the analysis. To our surprise, this new dataset - about an order of bigger than the size of the original dataset - shows, under standard assumptions, only mild evidence of an accelerated universe.
Aller guten Dinge sind drei: Cosmology with three interacting spin-2 fields
Lüben, Marvin; Amendola, Luca; Solomon, Adam R
2016-01-01
Theories of massive gravity with one or two dynamical metrics generically lack stable and observationally-viable cosmological solutions that are distinguishable from $\\Lambda$CDM. We consider an extension to trimetric gravity, with three interacting spin-2 fields which are not plagued by the Boulware-Deser ghost. We systematically explore every combination with two free parameters in search of background cosmologies that are competitive with $\\Lambda$CDM. For each case we determine whether the expansion history satisfies viability criteria, and whether or not it contains beyond-$\\Lambda$CDM phenomenology. Among the many models we consider, there are only three cases that seem to be both viable and distinguishable from standard cosmology. One of the models has only one free parameter and displays a crossing from above to below the phantom divide. The other two provide scaling behavior, although they contain future singularities that need to be studied in more detail. These models possess interesting features t...
Employment impacts of CDM projects in China's power sector
International Nuclear Information System (INIS)
There are continuous debates around the question of whether CDM really contributes to sustainable development (SD) in host countries. Employment impact is an essential indicator of SD. Based on an input-out approach this research builds a quantitative assessment model to evaluate the employment impacts of CDM. Both direct and indirect jobs creation and job losses of CDM projects in the power sector registered by the end of 2011 are calculated by project types and power grids where the project is located. Results of this study show that, although the above mentioned CDM projects causes about 99,000 net direct job losses, they also create about 3.08 million indirect jobs, resulting in the gross employment of CDM to be about 2.98 million. Thereof, hydro projects induce both direct and indirect job losses, which comes to approximately 0.89 million. Solar projects have the most potential since they own the highest indirect jobs created by one GWh generation, about 104 jobs/GWh. - Highlights: • An input–output model was built for assessment of CDM projects' employment impact; • CDM projects create direct and indirect jobs while cause some losses in short. • Significant indirect job gains of CDM projects were found; • Solar projects cause 104 jobs/GWh in average, ranking as the highest contributor
Sanders, RH; Papantonopoulos, E
2005-01-01
I discuss the classical cosmological tests, i.e., angular size-redshift, flux-redshift, and galaxy number counts, in the light of the cosmology prescribed by the interpretation of the CMB anisotropies. The discussion is somewhat of a primer for physicists, with emphasis upon the possible systematic
Moresco, Michele; Pozzetti, Lucia; Cimatti, Andrea; Jimenez, Raul; Maraston, Claudia; Verde, Licia; Thomas, Daniel; Citro, Annalisa; Tojeiro, Rita; Wilkinson, David
2016-05-01
Deriving the expansion history of the Universe is a major goal of modern cosmology. To date, the most accurate measurements have been obtained with Type Ia Supernovae (SNe) and Baryon Acoustic Oscillations (BAO), providing evidence for the existence of a transition epoch at which the expansion rate changes from decelerated to accelerated. However, these results have been obtained within the framework of specific cosmological models that must be implicitly or explicitly assumed in the measurement. It is therefore crucial to obtain measurements of the accelerated expansion of the Universe independently of assumptions on cosmological models. Here we exploit the unprecedented statistics provided by the Baryon Oscillation Spectroscopic Survey (BOSS, [1-3]) Data Release 9 to provide new constraints on the Hubble parameter H(z) using the cosmic chronometers approach. We extract a sample of more than 130000 of the most massive and passively evolving galaxies, obtaining five new cosmology-independent H(z) measurements in the redshift range 0.3 < z < 0.5, with an accuracy of ~11–16% incorporating both statistical and systematic errors. Once combined, these measurements yield a 6% accuracy constraint of H(z = 0.4293) = 91.8 ± 5.3 km/s/Mpc. The new data are crucial to provide the first cosmology-independent determination of the transition redshift at high statistical significance, measuring zt = 0.4 ± 0.1, and to significantly disfavor the null hypothesis of no transition between decelerated and accelerated expansion at 99.9% confidence level. This analysis highlights the wide potential of the cosmic chronometers approach: it permits to derive constraints on the expansion history of the Universe with results competitive with standard probes, and most importantly, being the estimates independent of the cosmological model, it can constrain cosmologies beyond—and including—the ΛCDM model.
The low mass end of the neutral gas mass and velocity width functions of galaxies in $\\Lambda$CDM
Yaryura, C Y; Abadi, M G; Starkenburg, E
2016-01-01
We use the high-resolution Aquarius cosmological dark matter simulations coupled to the semi-analytic model by Starkenburg et al. (2013) to study the HI content and velocity width properties of field galaxies at the low mass end in the context of $\\Lambda$CDM. We compare our predictions to the observed ALFALFA survey HI mass and velocity width functions, and find very good agreement without fine-tuning, when considering central galaxies. Furthermore, the properties of the dark matter halos hosting galaxies, characterised by their peak velocity and circular velocity at 2 radial disk scalelengths overlap perfectly with the inferred values from observations. This suggests that our galaxies are placed in the right dark matter halos, and consequently at face value, we do not find any discrepancy with the predictions from the $\\Lambda$CDM model. Our analysis indicates that previous tensions, apparent when using abundance matching models, arise because this technique cannot be straightforwardly applied for objects w...
Running cosmological constant with observational tests
Geng, Chao-Qiang; Zhang, Kaituo
2016-01-01
We investigate the running cosmological constant model with dark energy linearly proportional to the Hubble parameter, $\\Lambda = \\sigma H + \\Lambda_0$, in which the $\\Lambda$CDM limit is recovered by taking $\\sigma=0$. We derive the linear perturbation equations of gravity under the Friedmann-Lema\\"itre-Robertson-Walker cosmology, and show the power spectra of the CMB temperature and matter density distribution. By using the Markov chain Monte Carlo method, we fit the model to the current observational data and find that $\\sigma H_0/ \\Lambda_0 \\lesssim 2.63 \\times 10^{-2}$ and $6.74 \\times 10^{-2}$ for $\\Lambda(t)$ coupled to matter and radiation-matter, respectively, along with constraints on other cosmological parameters.
Running cosmological constant with observational tests
Directory of Open Access Journals (Sweden)
Chao-Qiang Geng
2016-09-01
Full Text Available We investigate the running cosmological constant model with dark energy linearly proportional to the Hubble parameter, Λ=σH+Λ0, in which the ΛCDM limit is recovered by taking σ=0. We derive the linear perturbation equations of gravity under the Friedmann–Lemaïtre–Robertson–Walker cosmology, and show the power spectra of the CMB temperature and matter density distribution. By using the Markov chain Monte Carlo method, we fit the model to the current observational data and find that σH0/Λ0≲2.63×10−2 and 6.74×10−2 for Λ(t coupled to matter and radiation-matter, respectively, along with constraints on other cosmological parameters.
Running cosmological constant with observational tests
Geng, Chao-Qiang; Lee, Chung-Chi; Zhang, Kaituo
2016-09-01
We investigate the running cosmological constant model with dark energy linearly proportional to the Hubble parameter, Λ = σH +Λ0, in which the ΛCDM limit is recovered by taking σ = 0. We derive the linear perturbation equations of gravity under the Friedmann-Lemaïtre-Robertson-Walker cosmology, and show the power spectra of the CMB temperature and matter density distribution. By using the Markov chain Monte Carlo method, we fit the model to the current observational data and find that σH0 /Λ0 ≲ 2.63 ×10-2 and 6.74 ×10-2 for Λ (t) coupled to matter and radiation-matter, respectively, along with constraints on other cosmological parameters.
Cosmology with Peculiar Velocities: Observational Effects
Andersen, Per; Howlett, Cullan
2016-01-01
In this paper we investigate how observational effects could possibly bias cosmological inferences from peculiar velocity measurements. Specifically, we look at how bulk flow measurements are compared with theoretical predictions. Usually bulk flow calculations try to approximate the flow that would occur in a sphere around the observer. Using the Horizon Run 2 simulation we show that the traditional methods for bulk flow estimation can overestimate the magnitude of the bulk flow for two reasons: when the survey geometry is not spherical (the data do not cover the whole sky), and when the observations undersample the velocity distributions. Our results may explain why several bulk flow measurements found bulk flow velocities that seem larger than those expected in standard {\\Lambda}CDM cosmologies. We recommend a different approach when comparing bulk flows to cosmological models, in which the theoretical prediction for each bulk flow measurement is calculated specifically for the geometry and sampling rate o...
CDM. Information and guidebook - Developed for the UNEP project 'CD4CDM'[Clean development nedianism
Energy Technology Data Exchange (ETDEWEB)
Lee, M.K. (ed.)
2003-12-01
Since the Clean Development Mechanism (CDM) was defined at Conference of the Parties 3 in Kyoto 1997, it took the international community another 4 years to reach the Marrakesh Accords in which the modalities and procedures to implement the CDM was elaborated. Even if more detailed rules, procedures and modalities have to be further developed a general framework to implement the CDM and other Kyoto mechanisms are now in place. This guidebook is produced to support the UNEP project 'Capacity Development for the Clean Development Mechanism'. Focus is on the CDM project cycle, the Project Design Document (PDD), and related issues such as sustainable development goals, financing and market intelligence. The appendices present frequently asked questions and answers, a short overview of existing guidelines and a possible future list of eligible CDM projects categories. (BA)
An analytic cosmology solution of Poincaré gauge gravity
Lu, Jianbo; Chee, Guoying
2016-06-01
A cosmology of Poincaré gauge theory is developed. An analytic solution is obtained. The calculation results agree with observation data and can be compared with the ΛCDM model. The cosmological constant puzzle is the coincidence and fine tuning problem are solved naturally at the same time. The cosmological constant turns out to be the intrinsic torsion and curvature of the vacuum universe, and is derived from the theory naturally rather than added artificially. The dark energy originates from geometry, includes the cosmological constant but differs from it. The analytic expression of the state equations of the dark energy and the density parameters of the matter and the geometric dark energy are derived. The full equations of linear cosmological perturbations and the solutions are obtained.
The entropy-corrected holographic dark energy in Brans-Dicke cosmology with varying mass fermions
Farajollahi, H.; Tayebi, F.
2013-07-01
We aim in this paper to study Brans-Dicke cosmology in the presence of varying mass fermions and a self-interaction potential. Furthermore, we also probe the entropy corrected holographic dark energy (ECHDE) in the model in two non-interacting and interacting scenarios. The model parameters are constrained by using the recent SNe Ia observational data and tested against observational data of Hubble parameter. For a comparison, we also constrained and tested the cosmological parameters in ΛCDM model with the same observational data. We show that in non of the scenarios the model prediction is better than ΛCDM model.
The screening Horndeski cosmologies
Starobinsky, Alexei A.; Sushkov, Sergey V.; Volkov, Mikhail S.
2016-06-01
We present a systematic analysis of homogeneous and isotropic cosmologies in a particular Horndeski model with Galileon shift symmetry, containing also a Λ-term and a matter. The model, sometimes called Fab Five, admits a rich spectrum of solutions. Some of them describe the standard late time cosmological dynamic dominated by the Λ-term and matter, while at the early times the universe expands with a constant Hubble rate determined by the value of the scalar kinetic coupling. For other solutions the Λ-term and matter are screened at all times but there are nevertheless the early and late accelerating phases. The model also admits bounces, as well as peculiar solutions describing ``the emergence of time''. Most of these solutions contain ghosts in the scalar and tensor sectors. However, a careful analysis reveals three different branches of ghost-free solutions, all showing a late time acceleration phase. We analyse the dynamical stability of these solutions and find that all of them are stable in the future, since all their perturbations stay bounded at late times. However, they all turn out to be unstable in the past, as their perturbations grow violently when one approaches the initial spacetime singularity. We therefore conclude that the model has no viable solutions describing the whole of the cosmological history, although it may describe the current acceleration phase. We also check that the flat space solution is ghost-free in the model, but it may acquire ghost in more general versions of the Horndeski theory.
Cosmic Constraints to wCDM Model from Strong Gravitational Lensing
An, Jie; Xu, Lixin
2016-01-01
In this paper, we study the cosmic constraint to $w$CDM model via $118$ strong gravitational lensing systems which are complied from SLACS, BELLS, LSD and SL2S surveys, where the ratio between two angular diameter distances $D^{obs} = D_A(z_l,z_s)/D_A(0,z_s)$ is taken as a cosmic observable. To obtain this ratio, we adopt two strong lensing models: one is the singular isothermal sphere model (SIS), the other one is the power-law density profile (PLP) model. Via the Markov Chain Mote Carlo method, the posterior distribution of the cosmological model parameters space is obtained. The results show that the cosmological model parameters are not sensitive to the parameterized forms of the power-law index $\\gamma$. Furthermore, the PLP model gives a relative tighter constraint to the cosmological parameters than that of the SIS model. The predicted value of $\\Omega_m=0.31^{+0.44}_{-0.24}$ by SIS model is compatible with that obtained by {\\it Planck}2015: $\\Omega_{m}=0.313\\pm0.013$. However, the value of $\\Omega_m=0...
The Lambda CDM-model in quantum field theory on curved spacetime and Dark Radiation
Hack, Thomas-Paul
2013-01-01
In the standard model of cosmology, the universe is described by a Robertson-Walker spacetime, while its matter/energy content is modeled by a perfect fluid with three components corresponding to matter/dust, radiation and a cosmological constant. On the other hand, in particle physics matter and radiation are described in terms of quantum field theory on Minkowski spacetime. We unify these seemingly different theoretical frameworks by analysing the standard model of cosmology from first principles within quantum field theory on curved spacetime: assuming that the universe is homogeneous and isotropic on large scales, we specify a class of quantum states whose expectation value of the energy density is qualitatively and quantitatively of the standard perfect fluid form up to potential corrections. Qualitatively, these corrections depend on new parameters not present in the standard Lambda CDM-model and can account for e.g. the phenomenon of Dark Radiation (N_eff>3.046), having a characteristic signature which...
Cosmic Emulation: The Concentration-Mass Relation for wCDM Universes
Kwan, Juliana; Heitmann, Katrin; Habib, Salman
2012-01-01
The concentration-mass relation for dark matter-dominated halos is one of the essential results expected from a theory of structure formation. We present a simple prediction scheme, a cosmic emulator, for the c-M relation as a function of cosmological parameters for wCDM models. The emulator is constructed from 37 individual models, with three nested N-body gravity-only simulations carried out for each model. The mass range covered by the emulator is 2 x 10^{12} M_sun < M <10^{15} M_sun with a corresponding redshift range of z=0 -1. Over this range of mass and redshift, as well as the variation of cosmological parameters studied, the mean halo concentration varies from c ~ 2 to c ~ 8. The distribution of the concentration at fixed mass is Gaussian with a standard deviation of one-third of the mean value, almost independent of cosmology, mass, and redshift over the ranges probed by the simulations. We compare results from the emulator with previously derived heuristic analytic fits for the c-M relation, ...
Observational Aspects of an Inhomogeneous Cosmology
Saulder, Christoph; Zeilinger, Werner W
2012-01-01
One of the biggest mysteries in cosmology is Dark Energy, which is required to explain the accelerated expansion of the universe within the standard model. But maybe one can explain the observations without introducing new physics, by simply taking one step back and re-examining one of the basic concepts of cosmology, homogeneity. In standard cosmology, it is assumed that the universe is homogeneous, but this is not true at small scales (<200 Mpc). Since general relativity, which is the basis of modern cosmology, is a non-linear theory, one can expect some backreactions in the case of an inhomogeneous matter distribution. Estimates of the magnitude of these backreactions (feedback) range from insignificant to being perfectly able to explain the accelerated expansion of the universe. In the end, the only way to be sure is to test predictions of inhomogeneous cosmological theories, such as timescape cosmology, against observational data. If these theories provide a valid description of the universe, one expe...
Probing Cosmology with Weak Lensing Minkowski Functionals
Kratochvil, Jan M; Wang, Sheng; Haiman, Zoltan; May, Morgan; Huffenberger, Kevin
2011-01-01
In this paper, we show that Minkowski Functionals (MFs) of weak gravitational lensing (WL) convergence maps contain significant non-Gaussian, cosmology-dependent information. To do this, we use a large suite of cosmological ray-tracing N-body simulations to create mock WL convergence maps, and study the cosmological information content of MFs derived from these maps. Our suite consists of 80 independent 512^3 N-body runs, covering seven different cosmologies, varying three cosmological parameters Omega_m, w, and sigma_8 one at a time, around a fiducial LambdaCDM model. In each cosmology, we use ray-tracing to create a thousand pseudo-independent 12 deg^2 convergence maps, and use these in a Monte Carlo procedure to estimate the joint confidence contours on the above three parameters. We include redshift tomography at three different source redshifts z_s=1, 1.5, 2, explore five different smoothing scales theta_G=1, 2, 3, 5, 10 arcmin, and explicitly compare and combine the MFs with the WL power spectrum. We fi...
Cosmological perturbations on the phantom brane
Bag, Satadru; Viznyuk, Alexander; Shtanov, Yuri; Sahni, Varun
2016-07-01
We obtain a closed system of equations for scalar perturbations in a multi-component braneworld. Our braneworld possesses a phantom-like equation of state at late times, weff Consequently, the quasi-static approximation of Koyama and Maartens provides a good fit to the exact results during the matter-dominated epoch. We find that the late-time growth of density perturbations on the brane proceeds at a faster rate than in ΛCDM. Additionally, the gravitational potentials Φ and Ψ evolve differently on the brane than in ΛCDM, for which Φ = Ψ. On the brane, by contrast, the ratio Φ/Ψ exceeds unity during the late matter-dominated epoch (z lesssim 50). These features emerge as smoking gun tests of phantom brane cosmology and allow predictions of this scenario to be tested against observations of galaxy clustering and large-scale structure.
Chiral Cosmological Models: Dark Sector Fields Description
Chervon, S V
2014-01-01
The present review is devoted to a Chiral Cosmological Model as the self-gravitating nonlinear sigma model with the potential of (self)interactions employed in cosmology. The chiral cosmological model has successive applications in descriptions of the inflationary epoch of the Universe evolution; the present accelerated expansion of the Universe also can be described by the chiral fields multiplet as the dark energy in wide sense. To be more illustrative we are often addressed to the two-component chiral cosmological model. Namely, the two-component chiral cosmological model describing the phantom field with interaction to a canonical scalar field is analyzed in details. New generalized model of quintom character is proposed and exact solutions are founded out. In the review we represented the perturbation theory for chiral cosmological model with the aim to describe the structure formation using the progress achieved in the inflation theory. It was shown that cosmological perturbations from chiral fields can...
Belinski, V
2009-01-01
The talk at international conference in honor of Ya. B. Zeldovich 95th Anniversary, Minsk, Belarus, April 2009. The talk represents a review of the old results and contemporary development on the problem of cosmological singularity.
Beyond lensing by the cosmological constant
Faraoni, Valerio
2016-01-01
The long-standing problem of whether the cosmological constant affects directly the deflection of light caused by a gravitational lens is reconsidered. We use a new approach based on the Hawking quasilocal mass of a sphere grazed by light rays and on its splitting into local and cosmological parts. Previous literature restricted to the cosmological constant is extended to any form of dark energy accelerating the universe in which the gravitational lens is embedded.
Understanding the shape and diversity of dwarf galaxy rotation curves in ΛCDM
Read, J. I.; Iorio, G.; Agertz, O.; Fraternali, F.
2016-11-01
The shape and diversity of dwarf galaxy rotation curves is at apparent odds with dark matter halos in a Λ Cold Dark Matter (ΛCDM) cosmology. We use mock data from isolated dwarf galaxy simulations to show that this owes to three main effects. Firstly, stellar feedback heats dark matter, leading to a `CORENFW' dark matter density profile with a slowly rising rotation curve. Secondly, if close to a recent starburst, large H I bubbles push the rotation curve out of equilibrium, deforming the rotation curve shape. Thirdly, when galaxies are viewed near face-on, their best fit inclination is biased high. This can lead to a very shallow rotation curve that falsely implies a large dark matter core. All three problems can be avoided, however, by a combination of improved mass models and a careful selection of target galaxies. Fitting our CORENFW model to mock rotation curve data, we show that we can recover the rotation curve shape, dark matter halo mass M200 and concentration parameter c within our quoted uncertainties. We fit our CORENFW model to real data for four isolated dwarf irregulars, chosen to span a wide range of rotation curve shapes. We obtain an excellent fit for NGC 6822 and WLM, with tight constraints on M200, and c consistent with ΛCDM. However, IC 1613 and DDO 101 give a poor fit. For IC 1613, we show that this owes to disequilibria and its uncertain inclination i; for DDO 101, it owes to its uncertain distance D. If we assume iIC1613 ˜ 15° and DDDO101 ˜ 12 Mpc, consistent with current uncertainties, we are able to fit both galaxies very well. We conclude that ΛCDM appears to give an excellent match to dwarf galaxy rotation curves.
Lesgourges, J.
2013-08-01
We present a self-contained summary of the theory of linear cosmological perturbations. We emphasize the effect of the six parameters of the minimal cosmological model, first, on the spectrum of Cosmic Microwave Background temperature anisotropies, and second, on the linear matter power spectrum. We briefly review at the end the possible impact of a few non-minimal dark matter and dark energy models.
Polytropic dark matter flows illuminate dark energy and accelerated expansion
Kleidis, K.; Spyrou, N. K.
2015-04-01
Currently, a large amount of data implies that the matter constituents of the cosmological dark sector might be collisional. An attractive feature of such a possibility is that, it can reconcile dark matter (DM) and dark energy (DE) in terms of a single component, accommodated in the context of a polytropic-DM fluid. In fact, polytropic processes in a DM fluid have been most successfully used in modeling dark galactic haloes, thus significantly improving the velocity dispersion profiles of galaxies. Motivated by such results, we explore the time evolution and the dynamical characteristics of a spatially-flat cosmological model, in which, in principle, there is no DE at all. Instead, in this model, the DM itself possesses some sort of fluidlike properties, i.e., the fundamental units of the Universe matter-energy content are the volume elements of a DM fluid, performing polytropic flows. In this case, together with all the other physical characteristics, we also take the energy of this fluid's internal motions into account as a source of the universal gravitational field. This form of energy can compensate for the extra energy, needed to compromise spatial flatness, namely, to justify that, today, the total energy density parameter is exactly unity. The polytropic cosmological model, depends on only one free parameter, the corresponding (polytropic) exponent, Γ. We find this model particularly interesting, because for Γ ≤ 0.541, without the need for either any exotic DE or the cosmological constant, the conventional pressure becomes negative enough so that the Universe accelerates its expansion at cosmological redshifts below a transition value. In fact, several physical reasons, e.g., the cosmological requirement for cold DM (CDM) and a positive velocity-of-sound square, impose further constraints on the value of Γ, which is eventually settled down to the range -0.089 < Γ ≤ 0. This cosmological model does not suffer either from the age problem or from the
Confusion in Cosmology and Gravitation
Corda, C.; Katebi, R.; Schmidt, N. O.
2016-06-01
In a series of papers, Santilli and collaborators released various strong statements against the general theory of relativity (GTR) and the standard ΛCDM model of cosmology. In this paper we show that such claims are due to misunderstandings of basic concepts of gravitation and cosmology. In particular, we show that Santilli and collaborators demonstrated neither that the GTR is wrong, nor that the Universe is not expanding. We also show that the so-called iso-gravitation theory (IGT) of Santilli is in macroscopic contrast with geodesic motion and, in turn, with the Equivalence Principle (EP) and must therefore be ultimately rejected. Finally, we show that, although the so called iso-redshift could represent an interesting alternative (similar to the tired light theory historically proposed by Zwicky) to the Universe expansion from a qualitative point of view, it must be rejected from a quantitative point of view because the effect of iso-redshift is 10-6 smaller than the effect requested to achieve the cosmological redshift.
Confusion in Cosmology and Gravitation
Corda, C.; Katebi, R.; Schmidt, N. O.
2016-10-01
In a series of papers, Santilli and collaborators released various strong statements against the general theory of relativity (GTR) and the standard ΛCDM model of cosmology. In this paper we show that such claims are due to misunderstandings of basic concepts of gravitation and cosmology. In particular, we show that Santilli and collaborators demonstrated neither that the GTR is wrong, nor that the Universe is not expanding. We also show that the so-called iso-gravitation theory (IGT) of Santilli is in macroscopic contrast with geodesic motion and, in turn, with the Equivalence Principle (EP) and must therefore be ultimately rejected. Finally, we show that, although the so called iso-redshift could represent an interesting alternative (similar to the tired light theory historically proposed by Zwicky) to the Universe expansion from a qualitative point of view, it must be rejected from a quantitative point of view because the effect of iso-redshift is 10-6 smaller than the effect requested to achieve the cosmological redshift.
Silk, Joseph
2008-11-01
The field of cosmology has been transformed since the glorious decades of the 1920's and 1930's when theory and observation converged to develop the current model of the expanding universe. It was a triumph of the theory of general relativity and astronomy. The first revolution came when the nuclear physicists entered the fray. This marked the debut of the hot big bang, in which the light elements were synthesized in the first three minutes. It was soon realised that elements like carbon and iron were synthesized in exploding stars. However helium, as well as deuterium and lithium, remain as George Gamow envisaged, the detritus of the big bang. The climax arrived with one of the most remarkable discoveries of the twentieth century, the cosmic microwave background radiation, in 1964. The fossil glow turned out to have the spectrum of an ideal black body. One could not imagine a stronger confirmation of the hot and dense origin of the universe. This discovery set the scene for the next major advance. It was now the turn of the particle physicists, who realized that the energies attained near the beginning of the universe, and unachievable in any conceivable terrestrial accelerator, provided a unique testing ground for theories of grand unification of the fundamental forces. This led Alan Guth and Andrei Linde in 1980 to propose the theory of inflation, which solved outstanding puzzles of the big bang. One could now understand why the universe is so large and homogeneous, and the origin of the seed fluctuations that gave rise to large-scale structure. A key prediction was that the universe should have Euclidean geometry, now verified to a precision of a few percent. Modern cosmology is firmly embedded in particle physics. It merits a text written by a particle physicist who can however appreciate the contributions of astronomy that provide the foundation and infrastructure for the theory of the expanding universe. There are now several such texts available. The most
How smooth are particle trajectories in a $\\Lambda$CDM Universe?
Rampf, Cornelius; Frisch, Uriel
2015-01-01
Very. Indeed, it is shown here that in a flat, cold dark matter (CDM) dominated Universe with positive cosmological constant ($\\Lambda$), modelled in terms of a Newtonian and collisionless fluid, particle trajectories are analytical in time (representable by a convergent Taylor series) until at least a finite time after decoupling. The time variable used for this statement is the cosmic scale factor, i.e., the "$a$-time", and not the cosmic time. For this, a Lagrangian-coordinates formulation of the Euler-Poisson equations is employed, originally used by Cauchy for 3-D incompressible flow. Temporal analyticity for $\\Lambda$CDM is found to be a consequence of novel explicit all-order recursion relations for the $a$-time Taylor coefficients of the Lagrangian displacement field, from which we derive the convergence of the $a$-time Taylor series. A lower bound for the $a$-time where analyticity is guaranteed and shell-crossing is ruled out is obtained, whose value depends only on $\\Lambda$ and on the initial spat...
Banik, Indranil
2016-01-01
We recently used an axisymmetric model of the Local Group (LG) to show that the observed positions and velocities of galaxies inside it are difficult to reconcile with the standard cosmological model, $\\Lambda$CDM (MNRAS, 459, 2237). We now extend this investigation using a 3D model of the LG. This makes it feasible to directly include several other mass concentrations within and just outside the LG e.g. M33 and IC 342, respectively. As before, LG dwarf galaxies are treated as test particles. Although our best-fitting 3D model yields different velocity predictions for individual galaxies, the overall picture remains unchanged. In particular, observed radial velocities (RVs) tend to exceed $\\Lambda$CDM model predictions. The typical mismatch is slightly higher than in our earlier axisymmetric analysis, with a root mean square value of $\\sim$50 km/s. \\emph{Our main finding is that including the 3D distribution of massive perturbing dark matter halos is unlikely to help greatly with the high velocity galaxy prob...
Cosmological perturbations in a mimetic matter model
Matsumoto, Jiro; Odintsov, Sergei D.; Sushkov, Sergey V.
2015-03-01
We investigate the cosmological evolution of a mimetic matter model with arbitrary scalar potential. The cosmological reconstruction—which is the method for constructing a model for an arbitrary evolution of the scale factor—is explicitly performed for different choices of potential. The cases where the mimetic matter model shows the evolution as cold dark matter (CDM), the w CDM model, dark matter and dark energy with a dynamical O m (z ) [where O m (z )≡[(H (z )/H0)2-1 ]/[(1 +z )3-1 ] ], and phantom dark energy with a phantom-nonphantom crossing are presented in detail. The cosmological perturbations for such evolutions are studied in the mimetic matter model. For instance, the evolution behavior of the matter density contrast (which is different than the usual one, i.e., δ ¨+2 H δ ˙-κ2ρ δ /2 =0 ) is investigated. The possibility of a peculiar evolution of δ in the model under consideration is shown. Special attention is paid to the behavior of the matter density contrast near the future singularity, where the decay of perturbations may occur much earlier than the singularity.
Cosmological Constraints on Higgs-Dilaton Inflation
Trashorras, Manuel; Garcia-Bellido, Juan
2016-01-01
We test the viability of the Higgs-Dilaton Model (HDM) compared to the cosmological constant ($\\Lambda$CDM) and evolving dark energy ($w_0 w_a$CDM) models, by using the latest cosmological data that includes the Cosmic Microwave Background temperature, polarization and lensing data from the Planck satellite (2015 release), the BICEP and Keck Array experiments, the Type Ia supernovae from the JLA catalog, the Baryon Acoustic Oscillations and finally, the Weak Lensing data from the CFHTLenS survey. We find that the values of all cosmological parameters allowed by the Higgs-Dilaton model Inflation are well within the \\textit{Planck 15} constraints. In particular, we have that $w_0 = -1.0001^{+0.0072}_{-0.0074}$, $w_a = 0.00^{+0.15}_{-0.16}$, $n_s = 0.9693^{+0.0083}_{-0.0082}$, $\\alpha_s = -0.001^{+0.013}_{-0.014}$ and $r_{0.05} = 0.0025^{+0.0017}_{-0.0016}$ (95\\%C.L.). We also place new stringent constraints on the couplings of the Higgs-Dilaton model and we find that $\\xi_\\chi < 0.00328$ and $\\xi_h/\\sqrt{\\la...
Dolgov, A D
2016-01-01
Recent astronomical discoveries of supermassive black holes (quasars), gamma-bursters, supernovae, and dust at high redshifts, z = (5 --10), are reviewed. Such a dense population of the early universe is at odds with the conventional mechanisms of its possible origin. Similar data from the contemporary universe, which are also in conflict with natural expectations, are considered too. Two possible mechanisms are suggested, at least one of which can potentially solve all these problems. As a by-product of the last model, an abundant cosmological antimatter may be created.
Cosmological perturbations in an effective and genuinely phantom dark energy Universe
Albarran, Imanol; Morais, João
2016-01-01
We carry out an analysis of the cosmological perturbations in general relativity for three different models which are good candidates to describe the current acceleration of the Universe. These three set-ups are described classically by perfect fluids with a phantom nature and represent deviations from the most widely accepted $\\Lambda$CDM model. In addition, each of the models under study induce different future singularities or abrupt events known as (i) Big Rip, (ii) Little Rip and (iii) Little Sibling of the Big Rip. Only the first one is regarded as a true singularity since it occurs at a finite cosmic time. For this reason, we refer to the others as abrupt events. With the aim to find possible footprints of this scenario in the Universe matter distribution, we not only obtain the evolution of the cosmological scalar perturbations but also calculate the matter power spectrum for each model. Finally, we constrain observationally these models using several measurements of the growth rate function, more pre...
Kaluza-Klein cosmological model in f(R, T) gravity with Λ(T)
Sahoo, P. K.; Mishra, B.; Tripathy, S. K.
2016-04-01
A class of Kaluza-Klein cosmological models in $f(R,T)$ theory of gravity have been investigated. In the work, we have considered the functional $f(R,T)$ to be in the form $f(R,T)=f(R)+f(T)$ with $f(R)=\\lambda R$ and $f(T)=\\lambda T$. Such a choice of the functional $f(R,T)$ leads to an evolving effective cosmological constant $\\Lambda$ which depends on the stress energy tensor. The source of the matter field is taken to be a perfect cosmic fluid. The exact solutions of the field equations are obtained by considering a constant deceleration parameter which leads two different aspects of the volumetric expansion namely a power law and an exponential volumetric expansion. Keeping an eye on the accelerating nature of the universe in the present epoch, the dynamics and physical behaviour of the models have been discussed. From statefinder diagnostic pair we found that the model with exponential volumetric expansion behaves more like a $\\Lambda$CDM model.
Experiences of project developers around CDM projects in South Africa
International Nuclear Information System (INIS)
Project developers in South Africa are puzzled with the long process of evaluating and registering their CDM projects. In addition to other obstacles, we find that South African big businesses are rather reluctant to engage in any new business activities such as CDM projects and municipalities often lack the necessary flexibility. This offers opportunities for small-scale project developers who spot the opportunities and find creative solutions to overcome these difficulties. - Highlights: • First paper analysing the experience of small project developers in South Africa. • Project developers in South Africa are puzzled with the long process. • South African big businesses are reluctant to engage in CDM projects. • Small-scale project developers spot opportunities and find creative solutions to overcome difficulties. • Also, we saw learning processes of South African administration in support of CDM projects
CDM/baryon isocurvature perturbations in a sneutrino curvaton model
Energy Technology Data Exchange (ETDEWEB)
Harigaya, Keisuke; Kawasaki, Masahiro [Kavli IPMU (WPI), TODIAS, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8583 (Japan); Hayakawa, Taku; Yokoyama, Shuichiro, E-mail: keisuke.harigaya@ipmu.jp, E-mail: taku1215@icrr.u-tokyo.ac.jp, E-mail: kawasaki@icrr.u-tokyo.ac.jp, E-mail: shuichiro@rikkyo.ac.jp [Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582 (Japan)
2014-10-01
Matter isocurvature perturbations are strictly constrained from cosmic microwave background observations. We study a sneutrino curvaton model where both cold dark matter (CDM)/baryon isocurvature perturbations are generated. In our model, total matter isocurvature perturbations are reduced since the CDM/baryon isocurvature perturbations compensate for each other. We show that this model can not only avoid the stringent observational constraints but also suppress temperature anisotropies on large scales, which leads to improved agreement with observations.
Simple inhomogeneous cosmological (toy) models
I., Eddy G Chirinos; Zimdahl, Winfried
2016-01-01
Based on the Lema\\^itre-Tolman-Bondi (LTB) metric we consider two flat inhomogeneous big-bang models. We aim at clarifying, as far as possible analytically, basic features of the dynamics of the simplest inhomogeneous models and to point out the potential usefulness of exact inhomogeneous solutions as generalizations of the homogeneous configurations of the cosmological standard model. We discuss explicitly partial successes but also potential pitfalls of these simplest models. Although primarily seen as toy models, the relevant free parameters are fixed by best-fit values using the Joint Light-curve Analysis (JLA)-sample data. On the basis of a likelihood analysis we find that a local hump provides a better description of the observations than a local void. Future redshift-drift measurements are discussed as a promising tool to discriminate between inhomogeneous configurations and the $\\Lambda$CDM model.
Planck 2015 results. XIII. Cosmological parameters
Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Bartolo, N.; Battaner, E.; Battye, R.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R.-R.; Chiang, H. C.; Chluba, J.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Combet, C.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Désert, F.-X.; Di Valentino, E.; Dickinson, C.; Diego, J. M.; Dolag, K.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dunkley, J.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Farhang, M.; Fergusson, J.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Gauthier, C.; Gerbino, M.; Ghosh, T.; Giard, M.; Giraud-Héraud, Y.; Giusarma, E.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Hamann, J.; Hansen, F. K.; Hanson, D.; Harrison, D. L.; Helou, G.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huang, Z.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leahy, J. P.; Leonardi, R.; Lesgourgues, J.; Levrier, F.; Lewis, A.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maggio, G.; Maino, D.; Mandolesi, N.; Mangilli, A.; Marchini, A.; Maris, M.; Martin, P. G.; Martinelli, M.; Martínez-González, E.; Masi, S.; Matarrese, S.; McGehee, P.; Meinhold, P. R.; Melchiorri, A.; Melin, J.-B.; Mendes, L.; Mennella, A.; Migliaccio, M.; Millea, M.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Pearson, T. J.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Popa, L.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rouillé d'Orfeuil, B.; Rowan-Robinson, M.; Rubiño-Martín, J. A.; Rusholme, B.; Said, N.; Salvatelli, V.; Salvati, L.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Seiffert, M. D.; Serra, P.; Shellard, E. P. S.; Spencer, L. D.; Spinelli, M.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Trombetti, T.; Tucci, M.; Tuovinen, J.; Türler, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, F.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; White, M.; White, S. D. M.; Wilkinson, A.; Yvon, D.; Zacchei, A.; Zonca, A.
2016-09-01
This paper presents cosmological results based on full-mission Planck observations of temperature and polarization anisotropies of the cosmic microwave background (CMB) radiation. Our results are in very good agreement with the 2013 analysis of the Planck nominal-mission temperature data, but with increased precision. The temperature and polarization power spectra are consistent with the standard spatially-flat 6-parameter ΛCDM cosmology with a power-law spectrum of adiabatic scalar perturbations (denoted "base ΛCDM" in this paper). From the Planck temperature data combined with Planck lensing, for this cosmology we find a Hubble constant, H0 = (67.8 ± 0.9) km s-1Mpc-1, a matter density parameter Ωm = 0.308 ± 0.012, and a tilted scalar spectral index with ns = 0.968 ± 0.006, consistent with the 2013 analysis. Note that in this abstract we quote 68% confidence limits on measured parameters and 95% upper limits on other parameters. We present the first results of polarization measurements with the Low Frequency Instrument at large angular scales. Combined with the Planck temperature and lensing data, these measurements give a reionization optical depth of τ = 0.066 ± 0.016, corresponding to a reionization redshift of z_re=8.8+1.7-1.4. These results are consistent with those from WMAP polarization measurements cleaned for dust emission using 353-GHz polarization maps from the High Frequency Instrument. We find no evidence for any departure from base ΛCDM in the neutrino sector of the theory; for example, combining Planck observations with other astrophysical data we find Neff = 3.15 ± 0.23 for the effective number of relativistic degrees of freedom, consistent with the value Neff = 3.046 of the Standard Model of particle physics. The sum of neutrino masses is constrained to ∑ mν CMB observations and many other astrophysical data sets.
Quintessential Maldacena-Maoz cosmologies
International Nuclear Information System (INIS)
Maldacena and Maoz have proposed a new approach to holographic cosmology based on Euclidean manifolds with disconnected boundaries. This approach appears, however, to be in conflict with the known geometric results [the Witten-Yau theorem and its extensions] on spaces with boundaries of non-negative scalar curvature. We show precisely how the Maldacena-Maoz approach evades these theorems. We also exhibit Maldacena-Maoz cosmologies with [cosmologically] more natural matter content, namely quintessence instead of Yang-Mills fields, thereby demonstrating that these cosmologies do not depend on a special choice of matter to split the Euclidean boundary. We conclude that if our Universe is fundamentally anti-de Sitter-like [with the current acceleration being only temporary], then this may force us to confront the holography of spaces with a connected bulk but a disconnected boundary. (author)
MOND cosmology from entropic force
International Nuclear Information System (INIS)
We derive the MOND cosmology which is uniquely corresponding to the original MOND at galaxy scales via entropic gravity method. It inherits the key merit of MOND, that is, it reduces the baryonic matter and non-baryonic dark matter into baryonic matter only. For the first time we obtain the critical parameter in MOND, i.e., the transition acceleration ac at cosmological scale. We thus solve the long-standing coincidence problem ac∼cH0. More interestingly, a term like age-graphic dark energy emerges naturally. In the frame of this MOND cosmology, we only need baryonic matter to describe both dark matter and dark energy in standard cosmology.
Cosmological Inflation: A Personal Perspective
Kazanas, Demos
2008-01-01
We present a brief review of Cosmological Inflation from the personal perspective of the speaker who almost 30 years ago proposed a way of resolving the problem of Cosmological Horizon by employing certain notions and developments from the field of High Energy Physics. Along with a brief introduction of the Horizon and Flatness problems of standard cosmology, this lecture concentrates on personal reminiscing of the notions and ideas that prevailed and influenced the author's thinking at the time. The lecture then touches upon some more recent developments related to the subject including exact solutions to conformal gravity that provide a first principles emergence of a characteristic acceleration in the universe and concludes with some personal views concerning the direction that the cosmology field has taken in the past couple of decades and certain speculations some notions that may indicate future directions of research.
Cosmological and Astrophysical Neutrino Mass Measurements
Abazajian, K N; Cooray, A; De Bernardis, F; Dodelson, S; Friedland, A; Fuller, G M; Hannestad, S; Keating, B G; Linder, E V; Lunardini, C; Melchiorri, A; Miquel, R; Pierpaoli, E; Pritchard, J; Serra, P; Takada, M; Wong, Y Y Y
2011-01-01
Cosmological and astrophysical measurements provide powerful constraints on neutrino masses complementary to those from accelerators and reactors. Here we provide a guide to these different probes, for each explaining its physical basis, underlying assumptions, current and future reach.
Analysis of registered CDM projects: potential removal of evidenced bottlenecks
Energy Technology Data Exchange (ETDEWEB)
Agosto, D.; Bombard, P.; Gostinelli, F.
2007-07-01
The Clean Development Mechanism (CDM) has developed during its first period of implementation, a distinctive set of patterns. The authors thought of concentrating on the CDM analysis in order to highlight potential remedies or reasons for given bottlenecks. In order to establish a sort of extensive SWOT analysis for CDMs, all the 356 projects actually (November 2006) registered at UNFCCC were examined, together with all the about 1000 PDDs presented to the UNFCCC but not registered yet. The CDM projects have been studied trying to cluster projects according to relevant characteristics, both from a technical and an economic point of view. Chosen indicators are meant to identify: more convenient/more diffused energy system for a CDM; reasons for a geographical distribution of different types of projects; potentials for a future exploitation of lower used technologies in CDM. Conclusions are drawn and appropriate tables and graphs presented. (1) the Baseline Emission Factor, combined to economic patterns, is the pivotal factor that characterizes both choices of host country and technology; (2) some technologies can exploit appropriately CDM scheme, whilst other technologies, are constrained by it. (3) there are still some important weak points: grouping of non Annex I countries; crediting period; criteria for the evaluation of sustainable development. (auth)
Energy Technology Data Exchange (ETDEWEB)
Wesson, P.S.
1979-10-01
The Cosmological Principle states: the universe looks the same to all observers regardless of where they are located. To most astronomers today the Cosmological Principle means the universe looks the same to all observers because density of the galaxies is the same in all places. A new Cosmological Principle is proposed. It is called the Dimensional Cosmological Principle. It uses the properties of matter in the universe: density (rho), pressure (p), and mass (m) within some region of space of length (l). The laws of physics require incorporation of constants for gravity (G) and the speed of light (C). After combining the six parameters into dimensionless numbers, the best choices are: 8..pi..Gl/sup 2/ rho/c/sup 2/, 8..pi..Gl/sup 2/ rho/c/sup 4/, and 2 Gm/c/sup 2/l (the Schwarzchild factor). The Dimensional Cosmological Principal came about because old ideas conflicted with the rapidly-growing body of observational evidence indicating that galaxies in the universe have a clumpy rather than uniform distribution. (SC)
Energy Technology Data Exchange (ETDEWEB)
Zhang, Jing-Fei; Geng, Jia-Jia; Zhang, Xin, E-mail: jfzhang@mail.neu.edu.cn, E-mail: gengjiajia163@163.com, E-mail: zhangxin@mail.neu.edu.cn [Department of Physics, College of Sciences, Northeastern University, Shenyang 110004 (China)
2014-10-01
The detection of the B-mode polarization of the cosmic microwave background (CMB) by the BICEP2 experiment implies that the tensor-to-scalar ratio r should be involved in the base standard cosmology. In this paper, we extend the ΛCDM r+neutrino/dark radiation models by replacing the cosmological constant with the dynamical dark energy with constant w. Four neutrino plus dark energy models are considered, i.e., the wCDM r ∑ m{sub ν}, wCDM r N{sub eff}, wCDM r ∑ m{sub ν} N{sub eff}, and wCDM r N{sub eff} m{sub ν,sterile}{sup eff} models. The current observational data considered in this paper include the Planck temperature data, the WMAP 9-year polarization data, the baryon acoustic oscillation data, the Hubble constant direct measurement data, the Planck Sunyaev-Zeldovich cluster counts data, the Planck CMB lensing data, the cosmic shear data, and the BICEP2 polarization data. We test the data consistency in the four cosmological models, and then combine the consistent data sets to perform joint constraints on the models. We focus on the constraints on the parameters w, ∑ m{sub ν}, N{sub eff}, and m{sub ν,sterile}{sup eff}.
Conspiratorial cosmology - the case against the Universe
Rachen, Jörg P
2013-01-01
Based on the cosmological results of the Planck Mission, we show that all parameters describing our Universe within the \\Lambda CDM model can be constructed from a small set of numbers known from conspiracy theory. Our finding is confirmed by recent data from high energy particle physics. This clearly demonstrates that our Universe is a plot initiated an unknown interest group or lodge. We analyse possible scenarios for this conspiracy, and conclude that the belief in the existence of our Universe is an illusion, as previously assumed by ancient philosophers, 20th century science fiction authors and contemporary film makers.
Cosmological Models and Renormalization Group Flow
Kristjansson, K. R.; Thorlacius, L.
2002-01-01
We study cosmological solutions of Einstein gravity with a positive cosmological constant in diverse dimensions. These include big-bang models that re-collapse, big-bang models that approach de Sitter acceleration at late times, and bounce models that are both past and future asymptotically de Sitter. The re-collapsing and the bounce geometries are all tall in the sense that entire spatial slices become visible to a comoving observer before the end of conformal time, while the accelerating bi...
Cosmological and astrophysical neutrino mass measurements
DEFF Research Database (Denmark)
Abazajian, K.N.; Calabrese, E.; Cooray, A.;
2011-01-01
Cosmological and astrophysical measurements provide powerful constraints on neutrino masses complementary to those from accelerators and reactors. Here we provide a guide to these different probes, for each explaining its physical basis, underlying assumptions, current and future reach.......Cosmological and astrophysical measurements provide powerful constraints on neutrino masses complementary to those from accelerators and reactors. Here we provide a guide to these different probes, for each explaining its physical basis, underlying assumptions, current and future reach....
Spurious Small-Scale Structure & Discreteness-Driven Relaxation in Cosmological Simulations
Power, Chris; Robotham, Aaron S. G.; Obreschkow, Danail; Hobbs, Alexander; Lewis, Geraint F.
2016-01-01
There is strong evidence that cosmological N-body simulations dominated by Warm Dark Matter (WDM) contain spurious or unphysical haloes, most readily apparent as regularly spaced low-mass haloes strung along filaments. We show that spurious haloes are a feature of traditional N-body simulations of cosmological structure formation models, including WDM and Cold Dark Matter (CDM) models, in which gravitational collapse proceeds in an initially anisotropic fashion, and arises naturally as a cons...
Tsamis, N. C.; Woodard, R. P.
2016-08-01
We study a class of nonlocal, action-based, and purely gravitational models. These models seek to describe a cosmology in which inflation is driven by a large, bare cosmological constant that is screened by the self-gravitation between the soft gravitons that inflation rips from the vacuum. Inflation ends with the Universe poised on the verge of gravitational collapse, in an oscillating phase of expansion and contraction that should lead to rapid reheating when matter is included. After the attainment of a hot, dense Universe the nonlocal screening terms become constant as the Universe evolves through a conventional phase of radiation domination. The onset of matter domination triggers a much smaller antiscreening effect that could explain the current phase of acceleration.
An Improved Cosmological Model
Tsamis, N C
2016-01-01
We study a class of non-local, action-based, and purely gravitational models. These models seek to describe a cosmology in which inflation is driven by a large, bare cosmological constant that is screened by the self-gravitation between the soft gravitons that inflation rips from the vacuum. Inflation ends with the universe poised on the verge of gravitational collapse, in an oscillating phase of expansion and contraction that should lead to rapid reheating when matter is included. After the attainment of a hot, dense universe the nonlocal screening terms become constant as the universe evolves through a conventional phase of radiation domination. The onset of matter domination triggers a much smaller anti-screening effect that could explain the current phase of acceleration.
Narimani, Ali; Scott, Douglas
2011-01-01
Although it is possible that some fundamental physical constants could vary in time, it is important to only consider dimensionless combinations, such as the fine structure constant or the equivalent coupling constant for gravity. Once all such dimensionless numbers have been given, then we can be sure that our cosmological picture is governed by the same physical laws as that of another civilization with an entirely different set of units. An additional feature of the standard model of cosmology raises an extra complication, namely that the epoch at which we live is a crucial part of the model. This can be defined by giving the value of any one of the evolving cosmological parameters. It takes some care to avoid inconsistent results for constraints on variable constants, which could be caused by effectively fixing more than one parameter today. We show examples of this effect by considering in some detail the physics of Big Bang nucleosynthesis, recombination and microwave background anisotropies, being care...
Inflationary Cosmologies from Compactification?
Wohlfarth, M N R
2004-01-01
We consider the compactification of (d+n)-dimensional pure gravity and of superstring/M-theory on an n-dimensional internal space to a d-dimensional FLRW cosmology, with spatial curvature k=-1,0,+1, in Einstein conformal frame. The internal space is taken to be a product of Einstein spaces, each of which is allowed to have arbitrary curvature and a time-dependent volume. By investigating the effective d-dimensional scalar potential, which is a sum of exponentials, it is shown that such compactifications, in the k=0,+1 cases, do not lead to large amounts of accelerating expansion of the scale factor of the resulting FLRW universe, and, in particular, not to inflation. The case k=-1 admits solutions with eternal accelerating expansion for which the acceleration, however, tends to zero at late times.
Information gains from cosmological probes
Grandis, S.; Seehars, S.; Refregier, A.; Amara, A.; Nicola, A.
2016-05-01
In light of the growing number of cosmological observations, it is important to develop versatile tools to quantify the constraining power and consistency of cosmological probes. Originally motivated from information theory, we use the relative entropy to compute the information gained by Bayesian updates in units of bits. This measure quantifies both the improvement in precision and the `surprise', i.e. the tension arising from shifts in central values. Our starting point is a WMAP9 prior which we update with observations of the distance ladder, supernovae (SNe), baryon acoustic oscillations (BAO), and weak lensing as well as the 2015 Planck release. We consider the parameters of the flat ΛCDM concordance model and some of its extensions which include curvature and Dark Energy equation of state parameter w. We find that, relative to WMAP9 and within these model spaces, the probes that have provided the greatest gains are Planck (10 bits), followed by BAO surveys (5.1 bits) and SNe experiments (3.1 bits). The other cosmological probes, including weak lensing (1.7 bits) and {H0} measures (1.7 bits), have contributed information but at a lower level. Furthermore, we do not find any significant surprise when updating the constraints of WMAP9 with any of the other experiments, meaning that they are consistent with WMAP9. However, when we choose Planck15 as the prior, we find that, accounting for the full multi-dimensionality of the parameter space, the weak lensing measurements of CFHTLenS produce a large surprise of 4.4 bits which is statistically significant at the 8 σ level. We discuss how the relative entropy provides a versatile and robust framework to compare cosmological probes in the context of current and future surveys.
Farooq, Omer; Crandall, Sara; Ratra, Bharat
2016-01-01
We compile an updated list of 28 independent measurements of the Hubble parameter $H(z)$ between redshifts $0.1 \\leq z \\leq 2.36$ and use them to place constraints on model parameters of constant and time-varying dark energy cosmological models, both spatially flat and curved. We use five models to measure the redshift of the cosmological deceleration-acceleration transition, $z_{\\rm da}$, from these $H(z)$ data. Within the error bars, the measured $z_{\\rm da}$ are insensitive to the model used, depending only on the value assumed for the Hubble constant $H_0$. The weighted mean of our measurements is $z_{\\rm da} = 0.74 \\pm 0.06\\ (0.86 \\pm 0.04)$ for $H_0 = 68 \\pm 2.8\\ (73.8 \\pm 2.4)$ km s$^{-1}$ Mpc$^{-1}$ and should provide a reasonably model-independent estimate of this cosmological parameter. The $H(z)$ data are consistent with the standard spatially-flat $\\Lambda$CDM cosmological model but do not rule out non-flat models or dynamical dark energy models.
Constraints on non-flat cosmologies with massive neutrinos after Planck 2015
Chen, Yun; Biesiada, Marek; Li, Song; Zhu, Zong-Hong
2016-01-01
We investigate two dark energy cosmological models (i.e., the $\\Lambda$CDM and $\\phi$CDM models) with massive neutrinos in both the spatially flat and non-flat scenarios, where in the $\\phi$CDM model the scalar field possesses an inverse power-law potential, $V(\\phi)\\propto {\\phi}^{-\\alpha}$ ($\\alpha>0$). Cosmic microwave background data from Planck 2015, baryon acoustic oscillations data from 6dFGS, SDSS-MGS, BOSS-LOWZ and BOSS CMASS-DR11, the JLA compilation of Type Ia supernova apparent magnitude observations, and the Hubble Space Telescope $H_0$ prior, are jointly employed to constrain the model parameters. In the spatially flat (non-flat) $\\Lambda$CDM model, the sum of neutrino masses is bounded as $\\Sigma m_{\
Cosmological electromagnetic fields and dark energy
Jimenez, Jose Beltran
2008-01-01
Understanding why the expansion of the universe is presently accelerating is one of the most important open questions in modern cosmology. In this work we show that the presence of a temporal electromagnetic field on cosmological scales generates an effective cosmological constant which could be responsible for the acceleration. Primordial electromagnetic quantum fluctuations produced during electroweak scale inflation could naturally explain the presence of this field and the measured value of the dark energy density. This mechanism could be discriminated from a true cosmological constant by observations of CMB and structure formation. In the same way as the presence of matter or radiation in the Universe breaks global Lorentz symmetry, the existence of dark energy could be signalling the breakdown of electromagnetic gauge invariance on cosmological scales.
Bulk scalar field in DGP braneworld cosmology
Ansari, Rizwan ul Haq
2007-01-01
We investigated the effects of bulk scalar field in the braneworld cosmological scenario. The Friedmann equations and acceleration condition in presence of the bulk scalar field for a zero tension brane and cosmological constant are studied. In DGP model the effective Einstein equation on the brane is obtained with bulk scalar field. The rescaled bulk scalar field on the brane in the DGP model behaves as an effective four dimensional field, thus standard type cosmology is recovered. In present study of the DGP model, the late-time accelerating phase of the universe can be explained .
Kobayashi, M A R; Yonehara, A; Kobayashi, Masakazu A.R.; Kamaya, Hideyuki; Yonehara, Atsunori
2005-01-01
The first galaxies in the Universe are built up where cold dark matter (CDM) forms large scale filamentary structure. Although the galaxies are expected to emit numerous Lya photons, they are surrounded by plentiful neutral hydrogen with a typical optical depth for Lya of ~10^5 (HI halos) before the era of cosmological reionization. The HI halo almost follows the cosmological Hubble expansion with some anisotropic corrections around the galaxy because of the gravitational attraction by the underlying CDM filament. In this paper, we investigate the detectability of the Lya emissions from the first galaxies, examining their dependence on viewing angles. Solving the Lya line transfer problem in an anisotropically expanding HI halo, we show that the escape probability from the HI halo is the largest in direction along the filament axis. If the Lya source is observed with a narrow-band filter, the difference of apparent Lya line luminosities among viewing angles can be a factor of > 40 at an extreme case. Furtherm...
Polytropic dark matter flows illuminate dark energy and accelerated expansion
Kleidis, K.; Spyrou, N. K.
2015-04-01
Currently, a large amount of data implies that the matter constituents of the cosmological dark sector might be collisional. An attractive feature of such a possibility is that, it can reconcile dark matter (DM) and dark energy (DE) in terms of a single component, accommodated in the context of a polytropic-DM fluid. In fact, polytropic processes in a DM fluid have been most successfully used in modeling dark galactic haloes, thus significantly improving the velocity dispersion profiles of galaxies. Motivated by such results, we explore the time evolution and the dynamical characteristics of a spatially-flat cosmological model, in which, in principle, there is no DE at all. Instead, in this model, the DM itself possesses some sort of fluidlike properties, i.e., the fundamental units of the Universe matter-energy content are the volume elements of a DM fluid, performing polytropic flows. In this case, together with all the other physical characteristics, we also take the energy of this fluid's internal motions into account as a source of the universal gravitational field. This form of energy can compensate for the extra energy, needed to compromise spatial flatness, namely, to justify that, today, the total energy density parameter is exactly unity. The polytropic cosmological model, depends on only one free parameter, the corresponding (polytropic) exponent, Γ. We find this model particularly interesting, because for Γ ≤ 0.541, without the need for either any exotic DE or the cosmological constant, the conventional pressure becomes negative enough so that the Universe accelerates its expansion at cosmological redshifts below a transition value. In fact, several physical reasons, e.g., the cosmological requirement for cold DM (CDM) and a positive velocity-of-sound square, impose further constraints on the value of Γ, which is eventually settled down to the range -0.089 standard candles, and most naturally interprets, not only when, but also why the Universe
Cosmology with the Square Kilometre Array by SKA-Japan
Yamauchi, Daisuke; Kohri, Kazunori; Namikawa, Toshiya; Oyama, Yoshihiko; Sekiguchi, Toyokazu; Shimabukuro, Hayato; Takahashi, Keitaro; Takahashi, Tomo; Yokoyama, Shuichiro; Yoshikawa, Kohji
2016-01-01
In the past several decades, the standard cosmological model has been established and its parameters have been measured to a high precision, while there are still many of the fundamental questions in cosmology; such as the physics in the very early Universe, the origin of the cosmic acceleration and the nature of the dark matter. The future world's largest radio telescope, Square Kilometre Array (SKA), will be able to open the new frontier of cosmology and will be one of the most powerful tools for cosmology in the next decade. The cosmological surveys conducted by the SKA would have the potential not only to answer these fundamental questions but also deliver the precision cosmology. In this article we briefly review the role of the SKA from the view point of the modern cosmology. The cosmology science led by the SKA-Japan Consortium (SKA-JP) Cosmology Science Working Group is also discussed.
Cosmology with the Square Kilometre Array by SKA-Japan
Yamauchi, Daisuke; Ichiki, Kiyotomo; Kohri, Kazunori; Namikawa, Toshiya; Oyama, Yoshihiko; Sekiguchi, Toyokazu; Shimabukuro, Hayato; Takahashi, Keitaro; Takahashi, Tomo; Yokoyama, Shuichiro; Yoshikawa, Kohji
2016-10-01
In the past several decades, the standard cosmological model has been established and its parameters have been measured to a high precision, while there are still many fundamental questions in cosmology; such as the physics in the very early universe, the origin of the cosmic acceleration, and the nature of dark matter. The forthcoming radio telescope, the Square Kilometre Array (SKA), which will be the world's largest, will be able to open a new frontier in cosmology and will be one of the most powerful tools for cosmology in the coming decade. The cosmological surveys conducted by the SKA would have the potential not only to answer these fundamental questions but also deliver precision cosmology. In this article we briefly review the role of the SKA from the viewpoint of modern cosmology. The cosmological science led by the SKA-Japan Consortium (SKA-JP) Cosmology Science Working Group is also discussed.
Cold Dark Matter Cosmology Conflicts with Fluid Mechanics and Observations
Directory of Open Access Journals (Sweden)
Carl H. Gibson
2008-01-01
Full Text Available Cold dark matter (CDM cosmology based on the Jeans 1902 criterion for gravitational instability gives predictions about the early universe contrary to fluid mechanics and observations. Jeans neglected viscosity, diffusivity, and turbulence: factors that determine gravitational structure formation and contradict small structures (CDM halos forming from non-baryonic dark matter particle candidates. From hydro-gravitational-dynamics (HGD cosmology, viscous-gravitational fragmentation produced supercluster (10^46 kg, cluster, and galaxy-mass (10^42 kg clouds in the primordial plasma with the large fossil density turbulence (3 ×10 ^ -17 kg m ^ -3 of the first fragmentation at 10^12 s, and a protogalaxy linear morphology reflecting maximum stretching on vortex lines of the plasma turbulence at plasma-gas transition at 10^13 s. Gas protogalaxies fragmented into proto-globular-star-cluster mass (10 ^36 kg clumps of protoplanet gas clouds that are now frozen as earth-mass (10^ 24-25 kg Jovian planets of the baryonic dark matter, about 30,000,000 rogue planets per star. Observations contradict the prediction of CDM hierarchical clustering cosmology that massive Population III first stars at 10^16 s existed but support the HGD prediction of gentle formation of small first stars in globular-star-clusters soon after 10^13 s.
Enqvist, K
2012-01-01
The very basics of cosmological inflation are discussed. We derive the equations of motion for the inflaton field, introduce the slow-roll parameters, and present the computation of the inflationary perturbations and their connection to the temperature fluctuations of the cosmic microwave background.
Long-term prospects of CDM and JI; Langfristige Perspektiven von CDM und JI
Energy Technology Data Exchange (ETDEWEB)
Cames, Martin; Anger, Niels; Boehringer, Christoph; Harthan, Ralph O.; Schneider, Lambert [Oeko-Institut, Berlin (Germany)
2007-07-15
This study analyses whether Germany should use the flexible mechanisms under the Kyoto protocol or whether it should continue to achieve its greenhouse gas reduction targets by dint of domestic policies and measures. It estimates the future potential of the project-based Kyoto mechanisms (CDM and JI) and the impacts of its use on the German and the global economy, using an integrated-assessment model. In a Delphi survey, the expectations of international experts on the future prospects of the project-based Kyoto mechanisms are assessed. The study finishes with an analysis of options for promoting the use of the flexible mechanisms in Germany and concludes that the Federal Government of Germany should establish a project-based mechanisms fund of 25 to 50 million Kyoto units to cover the compliance uncertainties due to unexpected temperature or business cycle variations. (orig.) [German] Diese Studie untersucht, ob Deutschland die flexiblen Mechanismen unter dem Kyoto-Protokoll nutzen sollte oder weiterhin seine Treibhausgasreduktionsziele durch inlaendische Politiken und Massnahmen erreichen sollte. Das kuenftige Potenzial der projektbezogenen Kyoto-Mechanismen (CDM und JI) wird untersucht und die Auswirkungen von deren Nutzung auf die deutsche und globale Wirtschaft werden mit einem Integrated-Assessment-Modell abgeschaetzt. In einer Delphi-Befragung werden die Erwartungen internationaler Experten in Hinblick auf die kuenftigen Perspektiven der projektbezogenen Kyoto- Mechanismen ermittelt. Abschliessend werden Moeglichkeiten zur Foerderung der Nutzung der flexiblen Mechanismen in Deutschland analysiert, mit der Schlussfolgerung, dass die Bundesregierung einen 25 bis 50 Millionen Kyoto-Einheiten umfassenden Fonds fuer projektbezogene Mechanismen einrichten sollte, um die Unsicherheiten bei der Erfuellung des Kyoto-Ziels infolge unerwarteter Temperaturschwankungen oder einer Aenderung der Konjunkturentwicklung abzudecken. (orig.)
Genetically modified halos: towards controlled experiments in $\\Lambda$CDM galaxy formation
Roth, Nina; Peiris, Hiranya V
2015-01-01
We propose a method to generate `genetically-modified' (GM) initial conditions for high-resolution simulations of galaxy formation in a cosmological context. Building on the Hoffman-Ribak algorithm, we start from a reference simulation with fully random initial conditions, then make controlled changes to specific properties of a single halo (such as its mass and merger history). The algorithm demonstrably makes minimal changes to other properties of the halo and its environment, allowing us to isolate the impact of a given modification. As a significant improvement over previous work, we are able to calculate the abundance of the resulting objects relative to the $\\Lambda$CDM reference cosmology. Our approach can be applied to a wide range of cosmic structures and epochs; here we study two problems as a proof-of-concept. First, we investigate the change in density profile and concentration as the collapse time of three individual halos are varied at fixed final mass, showing good agreement with previous stati...
Cosmological Constant or Variable Dark Energy?
Institute of Scientific and Technical Information of China (English)
XU Li-Xin; ZHANG Cheng-Wu; LIU Hong-Ya
2007-01-01
@@ Selection statics of the Akaike information criterion (AIC) model and the Bayesian information criterion (BIC)model are applied to the Λ-cold dark matter (ΛCDM) cosmological model, the constant equation of state of dark energy, w =constant, and the parametrized equation of state of dark energy, w(z) = w0 + w1z/(1 + z),to determine which one is the better cosmological model to describe the evolution of the universe by combining the recent cosmic observational data including Sne Ia, the size of baryonic acoustic oscillation (BAO) peak from SDSS, the three-year WMAP CMB shift parameter. The results show that AIC, BIC and current datasets are not powerful enough to discriminate one model from the others, though odds suggest differences between them.
Sollerman, J; Davis, T M; Blomqvis, M; Bassett, B; Becker, A C; Cinabro, D; Filippenko, A V; Foley, R J; Frieman, J; Garnavich, P; Lampeitl, H; Marriner, J; Miquel, R; Nichol, R C; Richmond, M W; Sako, M; Schneider, D P; Smith, M; Vanderplas, J T; Wheeler, J C
2009-01-01
We use the new SNe Ia discovered by the SDSS-II Supernova Survey together with additional supernova datasets as well as observations of the cosmic microwave background and baryon acoustic oscillations to constrain cosmological models. This complements the analysis presented by Kessler et al. in that we discuss and rank a number of the most popular non-standard cosmology scenarios. When this combined data-set is analyzed using the MLCS2k2 light-curve fitter, we find that more exotic models for cosmic acceleration provide a better fit to the data than the Lambda-CDM model. For example, the flat DGP model is ranked higher by our information criteria tests than the standard model. When the dataset is instead analyzed using the SALT-II light-curve fitter, the standard cosmological constant model fares best. Our investigation also includes inhomogeneous Lemaitre-Tolman-Bondi (LTB) models. While our LTB models can be made to fit the supernova data as well as any other model, the extra parameters they require are not...
Galactic cannibalism and CDM density profiles
Nipoti, C; Ciotti, L; Stiavelli, M
2004-01-01
Using N-body simulations we show that the process of formation of the brightest cluster galaxy through dissipationless galactic cannibalism can affect the inner cluster dark matter density profile. In particular, we use as realistic test case the dynamical evolution of the galaxy cluster C0337-2522 at redshift z=0.59, hosting in its centre a group of five elliptical galaxies which are likely to be the progenitor of a central giant elliptical. After the formation of the brightest cluster galaxy, the inner cluster dark matter density profile is significantly flatter (logarithmic slope 0.48
Marsh, David J. E.
2016-07-01
Axions comprise a broad class of particles that can play a major role in explaining the unknown aspects of cosmology. They are also well-motivated within high energy physics, appearing in theories related to CP-violation in the standard model, supersymmetric theories, and theories with extra-dimensions, including string theory, and so axion cosmology offers us a unique view onto these theories. I review the motivation and models for axions in particle physics and string theory. I then present a comprehensive and pedagogical view on the cosmology and astrophysics of axion-like particles, starting from inflation and progressing via BBN, the CMB, reionization and structure formation, up to the present-day Universe. Topics covered include: axion dark matter (DM); direct and indirect detection of axions, reviewing existing and future experiments; axions as dark radiation; axions and the cosmological constant problem; decays of heavy axions; axions and stellar astrophysics; black hole superradiance; axions and astrophysical magnetic fields; axion inflation, and axion DM as an indirect probe of inflation. A major focus is on the population of ultralight axions created via vacuum realignment, and its role as a DM candidate with distinctive phenomenology. Cosmological observations place robust constraints on the axion mass and relic density in this scenario, and I review where such constraints come from. I next cover aspects of galaxy formation with axion DM, and ways this can be used to further search for evidence of axions. An absolute lower bound on DM particle mass is established. It is ma > 10-24eV from linear observables, extending to ma ≳ 10-22eV from non-linear observables, and has the potential to reach ma ≳ 10-18eV in the future. These bounds are weaker if the axion is not all of the DM, giving rise to limits on the relic density at low mass. This leads to the exciting possibility that the effects of axion DM on structure formation could one day be detected
Late time cosmic acceleration from natural infrared cutoff?
Gorji, Mohammad Ali
2016-01-01
In this paper, inspired by the ultraviolet deformation of the Friedmann-Lema\\^{\\i}tre-Robertson-Walker geometry in loop quantum cosmology, we formulate an infrared-modified cosmological model. We obtain the associated deformed Friedmann and Raychaudhuri equations and we show that the late time cosmic acceleration can be addressed by the infrared corrections. As a particular example, we applied the setup to the case of matter dominated universe. This model has the same number of parameters as $\\Lambda$CDM, but a dynamical dark energy generates in the matter dominated era at the late time. According to our model, as the universe expands, the energy density of the cold dark matter dilutes and when the Hubble parameter approaches to its minimum, the infrared effects dominate such that the effective equation of state parameter smoothly changes from $w_{_{\\rm eff}}=0$ to $w_{_{\\rm eff}}=-2$. Interestingly and nontrivially, the unstable de Sitter phase with $w_{_{\\rm eff}}=-1$ is corresponding to $\\Omega_m=\\Omega_d ...
Future Evolution of Bound Superclusters in an Accelerating Universe
Araya-Melo, Pablo A; Meza, Andres; van de Weygaert, Rien; Dünner, Rolando; Quintana, Hernan
2008-01-01
The evolution of marginally bound supercluster-like objects in an accelerating Universe, with Omega_l = 0.7 and Omega_m = 0.3, is followed from the present time to an expansion factor a = 100. The large scale evolution of these objects freezes shortly after the present cosmological epoch, in contrast to the vigorously continuing internal development. Our study follows the external and the internal evolution of these island universes, as they gradually detach themselves from the cosmic background and internally evolve in splendid isolation. We model the bound objects in a LambdaCDM cosmological simulation of 512^3 dark matter particles in a cube of 500 Mpc/h side length. The objects are identified on the basis of the binding density criterion introduced by Dunner et al. (2006). In our simulation we find one supercluster with a mass of M ~ 8x10^15 M_sun/h, slightly larger than that of the Shapley supercluster. Even though we find around two Shapley-like superclusters in a volume comparable to that of the Local ...
Options for utilizing the CDM for global emission reductions
Energy Technology Data Exchange (ETDEWEB)
Butzengeiger-Geyer, Sonja; Castro, Paula; Harthan, Ralph O.; Hayashi, Daisuke; Healy, Sean; Maribu, Karl Magnus; Michaelowa, Axel; Okubo, Yuri; Schneider, Lambert; Storroe, Ingunn [Zuerich Univ. (Switzerland); Oeko-Institut e.V., Berlin (Germany); Perspectives GmbH, Hamburg (Germany); Point Carbon A/S, Oslo (Norway)
2010-11-15
The study describes and discusses in detail how four CDM reform alternatives, namely discounting of emission reductions, ambitious baselines, purchase and cancellation of CERs and reinvestment of CER levies, could be integrated in a Post-2012 climate regime. The study assesses these alternatives, according to their impacts on GHG emission reductions, contribution to sustainable development, cost-efficiency, technical feasibility, incentives and distributional effects as well as negotiability. The study shows that the introduction of discounting and ambitious baselines is technically feasible but politically a massive challenge. With the help of an economic model the study shows that the introduction of reform alternatives increases the amount of emission reductions but in comparison to the current CDM the impact is rather limited. But a CDM reform can in any case increase the credibility and improve the environmental integrity of the mechanism. (orig.)
Suitable scheme study of Chinese Building Energy Efficiency CDM Projects
Huang, Beijia; Yang, Haizhen; Wang, Shaoping; Wang, Feng
2010-11-01
China has great potential to develop Building Energy Efficiency Clean Development Mechanism (BEE CDM) projects, although have many challenges. Our results show that large-scale public buildings and urban residential buildings have relatively high BEE CDM potential, when comparing their characteristics to the CDM project requirements. The building enclosure, illumination energy conservation, air condition energy saving, solar thermal, and solar photovoltaic technology have relatively high application potential while considering the energy saving potential and marginal emission reduction cost. Case study of large-scale buildings shows that technology integration of building enclosure, illumination energy conservation, air condition energy saving, solar thermal can reduce required building number to 130 in order to meet the 1×105 tCO2 e/a reduction criteria. Some suggestions are also given in this paper.
Heitmann, Katrin; White, Martin; Habib, Salman; Williams, Brian J; Wagner, Christian
2009-01-01
The power spectrum of density fluctuations is a foundational source of cosmological information. Precision cosmological probes targeted primarily at investigations of dark energy require accurate theoretical determinations of the power spectrum in the nonlinear regime. To exploit the observational power of future cosmological surveys, accuracy demands on the theory are at the one percent level or better. Numerical simulations are currently the only way to produce sufficiently error-controlled predictions for the power spectrum. The very high computational cost of (precision) N-body simulations is a major obstacle to obtaining predictions in the nonlinear regime, while scanning over cosmological parameters. Near-future observations, however, are likely to provide a meaningful constraint only on constant dark energy equation of state 'wCDM' cosmologies. In this paper we demonstrate that a limited set of only 37 cosmological models -- the "Coyote Universe" suite -- can be used to predict the nonlinear matter pow...
Seeing darkness: the new cosmology
International Nuclear Information System (INIS)
We present some useful ways to visualize the nature of dark energy and the effects of the accelerating expansion on cosmological quantities. Expansion probes such as Type Ia supernovae distances and growth probes such as weak gravitational lensing and the evolution of large scale structure provide powerful tests in complementarity. We present a 'ladder' diagram, showing that in addition to dramatic improvements in precision, next generation probes will provide insight through an increasing ability to test assumptions of the cosmological framework, including gravity beyond general relativity
Cosmological evolution in exponential gravity
Energy Technology Data Exchange (ETDEWEB)
Bamba, Kazuharu; Geng, Chao-Qiang; Lee, Chung-Chi, E-mail: bamba@phys.nthu.edu.tw, E-mail: geng@phys.nthu.edu.tw, E-mail: g9522545@oz.nthu.edu.tw [Department of Physics, National Tsing Hua University, Hsinchu, Taiwan (China)
2010-08-01
We explore the cosmological evolution in the exponential gravity f(R) = R+c{sub 1}(1−e{sup −c{sub 2}R}) (c{sub 1,2} = constant). We summarize various viability conditions and explicitly demonstrate that the late-time cosmic acceleration following the matter-dominated stage can be realized. We also study the equation of state for dark energy and confirm that the crossing of the phantom divide from the phantom phase to the non-phantom (quintessence) one can occur. Furthermore, we illustrate that the cosmological horizon entropy globally increases with time.
Cosmological evolution in exponential gravity
Bamba, Kazuharu; Lee, Chung-Chi
2010-01-01
We explore the cosmological evolution in the exponential gravity $f(R)=R +c_1 \\left(1-e^{- c_2 R} \\right)$ ($c_{1, 2} = \\mathrm{constant}$). We summarize various viability conditions and explicitly demonstrate that the late-time cosmic acceleration following the matter-dominated stage can be realized. We also study the equation of state for dark energy and confirm that the crossing of the phantom divide from the phantom phase to the non-phantom (quintessence) one can occur. Furthermore, we illustrate that the cosmological horizon entropy globally increases with time.
MOND cosmology from entropic force
Zhang, Hongsheng; Li, Xin-Zhou
2011-01-01
We derive the MOND cosmology which is uniquely corresponding to the original MOND at galaxy scales via entropic gravity method. It inherits the key merit of MOND, that is, it reduces the baryonic matter and non-baryonic dark matter into baryonic matter only. For the first time we obtain the critical parameter in MOND, i.e., the transition acceleration $a_c$ at cosmological scale. We thus solve the long-standing coincidence problem $a_c\\sim cH_{0}$. More interestingly, a term like age-graphic ...
Neves, J C S
2015-01-01
In the Nietzschean philosophy, the concept of force from physics is important to build one of its main concepts: the will to power. The concept of force, which Nietzsche found out in the Classical Mechanics, almost disappears in the physics of the XX century with the Quantum Field Theory and General Relativity. Is the Nietzschean world as contending forces, a Dionysian cosmology, possible in the current science?
Kirillov, A A
2015-01-01
We describe in details the procedure how the Lobachevsky space can be factorized to a space of the constant negative curvature filled with a gas of wormholes. We show that such wormholes have throat sections in the form of tori and are traversable and stable in the cosmological context. The relation of such wormholes to the dark matter phenomenon is briefly described. We also discuss the possibility of the existence of analogous factorizations for all types of homogeneous spaces.
Kirillov, A. A.; Savelova, E. P.
2016-05-01
We describe in details the procedure how the Lobachevsky space can be factorized to a space of the constant negative curvature filled with a gas of wormholes. We show that such wormholes have throat sections in the form of tori and are traversable and stable in the cosmological context. The relation of such wormholes to the dark matter phenomenon is briefly described. We also discuss the possibility of the existence of analogous factorizations for all types of homogeneous spaces.
Grant, E.; Murdin, P.
2000-11-01
During the early Middle Ages (ca 500 to ca 1130) scholars with an interest in cosmology had little useful and dependable literature. They relied heavily on a partial Latin translation of PLATO's Timaeus by Chalcidius (4th century AD), and on a series of encyclopedic treatises associated with the names of Pliny the Elder (ca AD 23-79), Seneca (4 BC-AD 65), Macrobius (fl 5th century AD), Martianus ...
Chen, Pisin
2014-01-01
Recent years have seen tremendous progress in our understanding of the cosmos, which in turn points to even deeper questions to be further addressed. Concurrently the laser technology has undergone dramatic revolutions, providing exciting opportunity for science applications. History has shown that the symbiosis between direct observations and laboratory investigation is instrumental in the progress of astrophysics. We believe that this remains true in cosmology. Current frontier phenomena re...
Capozziello, S; Fatibene, L; Ferraris, M; Garruto, S
2016-01-01
We shall discuss cosmological models in extended theories of gravitation. We shall define a surface, called the model surface, in the space of observable parameters which characterises families of theories. We also show how this surface can be used to compare with observations. The model surface can potentially be used to falsify whole families of models instead reasoning on a single model basis as it is usually done by best fit arguments with observations.
10 lessons from 10 years of the CDM
Shishlov, Igor; Bellassen, Valentin
2012-01-01
The Clean Development Mechanism (CDM) is the first and by far the largest carbon offset instrument in the world. To date, it is the only market based on an environmental commodity which managed to attract several billions of euros of private capital on an annual basis. Being the first-of-a-kind climate change mitigation instrument, the CDM followed a "learning by doing" pattern undergoing numerous reforms throughout its more than 10-year history. Although the post-2012 fate of the mechanism r...
How to Improve the Likelihood of CDM Approval?
DEFF Research Database (Denmark)
Brandt, Urs Steiner; Svendsen, Gert Tinggaard
2014-01-01
How can the likelihood of Clean Development Mechanism (CDM) approval be improved in the face of institutional shortcomings? To answer this question, we focus on the three institutional shortcomings of income sharing, risk sharing and corruption prevention concerning afforestation/reforestation (A....../R). Furthermore, three main stakeholders are identified, namely investors, governments and agents in a principal-agent model regarding monitoring and enforcement capacity. Developing countries such as West Africa have, despite huge potentials, not been integrated in A/R CDM projects yet. Remote sensing, however...
Cosmology and astrophysics from relaxed galaxy clusters - II. Cosmological constraints
Mantz, A. B.; Allen, S. W.; Morris, R. G.; Rapetti, D. A.; Applegate, D. E.; Kelly, P. L.; von der Linden, A.; Schmidt, R. W.
2014-05-01
This is the second in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters. The data set employed here consists of Chandra observations of 40 such clusters, identified in a comprehensive search of the Chandra archive for hot (kT ≳ 5 keV), massive, morphologically relaxed systems, as well as high-quality weak gravitational lensing data for a subset of these clusters. Here we present cosmological constraints from measurements of the gas mass fraction, fgas, for this cluster sample. By incorporating a robust gravitational lensing calibration of the X-ray mass estimates, and restricting our measurements to the most self-similar and accurately measured regions of clusters, we significantly reduce systematic uncertainties compared to previous work. Our data for the first time constrain the intrinsic scatter in fgas, 7.4 ± 2.3 per cent in a spherical shell at radii 0.8-1.2 r2500 (˜1/4 of the virial radius), consistent with the expected level of variation in gas depletion and non-thermal pressure for relaxed clusters. From the lowest redshift data in our sample, five clusters at z 1, we obtain consistent results for Ωm and interesting constraints on dark energy: Ω _{{Λ }}=0.65^{+0.17}_{-0.22}> for non-flat ΛCDM (cosmological constant) models, and w = -0.98 ± 0.26 for flat models with a constant dark energy equation of state. Our results are both competitive and consistent with those from recent cosmic microwave background, Type Ia supernova and baryon acoustic oscillation data. We present constraints on more complex models of evolving dark energy from the combination of fgas data with these external data sets, and comment on the possibilities for improved fgas constraints using current and next-generation X-ray observatories and lensing data.
Cosmology with superluminous supernovae
Scovacricchi, D.; Nichol, R. C.; Bacon, D.; Sullivan, M.; Prajs, S.
2016-02-01
We predict cosmological constraints for forthcoming surveys using superluminous supernovae (SLSNe) as standardizable candles. Due to their high peak luminosity, these events can be observed to high redshift (z ˜ 3), opening up new possibilities to probe the Universe in the deceleration epoch. We describe our methodology for creating mock Hubble diagrams for the Dark Energy Survey (DES), the `Search Using DECam for Superluminous Supernovae' (SUDSS) and a sample of SLSNe possible from the Large Synoptic Survey Telescope (LSST), exploring a range of standardization values for SLSNe. We include uncertainties due to gravitational lensing and marginalize over possible uncertainties in the magnitude scale of the observations (e.g. uncertain absolute peak magnitude, calibration errors). We find that the addition of only ≃100 SLSNe from SUDSS to 3800 Type Ia Supernovae (SNe Ia) from DES can improve the constraints on w and Ωm by at least 20 per cent (assuming a flat wCDM universe). Moreover, the combination of DES SNe Ia and 10 000 LSST-like SLSNe can measure Ωm and w to 2 and 4 per cent, respectively. The real power of SLSNe becomes evident when we consider possible temporal variations in w(a), giving possible uncertainties of only 2, 5 and 14 per cent on Ωm, w0 and wa, respectively, from the combination of DES SNe Ia, LSST-like SLSNe and Planck. These errors are competitive with predicted Euclid constraints, indicating a future role for SLSNe for probing the high-redshift Universe.
Averaging anisotropic cosmologies
Barrow, J D; Barrow, John D.; Tsagas, Christos G.
2006-01-01
We examine the effects of spatial inhomogeneities on irrotational anisotropic cosmologies by looking at the average properties of pressure-free Bianchi-type models. Adopting the Buchert averaging scheme, we identify the kinematic backreaction effects by focussing on spacetimes with zero or isotropic spatial curvature. This allows us to close the system of the standard scalar formulae with a propagation equation for the shear magnitude. We find no change in the already known conditions for accelerated expansion. The backreaction terms are expressed as algebraic relations between the mean-square fluctuations of the models' irreducible kinematical variables. Based on these we investigate the early evolution of averaged vacuum Bianchi type $I$ universes and those filled with pressureless matter. In the latter case we show that the backreaction effects can modify the familiar Kasner-like singularity and potentially remove Mixmaster-type oscillations. We also discuss the possibility of accelerated expansion due to ...
The screening Horndeski cosmologies
Starobinsky, Alexei A; Volkov, Mikhail S
2016-01-01
We present a systematic analysis of homogeneous and isotropic cosmologies in a particular Horndeski model with Galileon shift symmetry, containing also a $\\Lambda$-term and a matter. The model, sometimes called Fab Five, admits a rich spectrum of solutions. Some of them describe the standard late time cosmological dynamic dominated by the $\\Lambda$-term and matter, while at the early times the universe expands with a constant Hubble rate determined by the value of the scalar kinetic coupling. For other solutions the $\\Lambda$-term and matter are screened at all times but there are nevertheless the early and late accelerating phases. The model also admits bounces, as well as peculiar solutions describing "the emergence of time". Most of these solutions contain ghosts in the scalar and tensor sectors. However, a careful analysis reveals three different branches of ghost-free solutions, all showing a late time acceleration phase. We analyze the dynamical stability of these solutions and find that all of them are...
Sehgal, Neelima; Acquaviva, Viviana; Ade, Peter A R; Aguirre, Paula; Amiri, Mandana; Appel, John W; Barrientos, L Felipe; Battistelli, Elia S; Bond, J Richard; Brown, Ben; Burger, Bryce; Chervenak, Jay; Das, Sudeep; Devlin, Mark J; Dicker, Simon R; Doriese, W Bertrand; Dunkley, Joanna; Dünner, Rolando; Essinger-Hileman, Thomas; Fisher, Ryan P; Fowler, Joseph W; Hajian, Amir; Halpern, Mark; Hasselfield, Matthew; Hernández-Monteagudo, Carlos; Hilton, Gene C; Hilton, Matt; Hincks, Adam D; Hlozek, Renée; Holtz, David; Huffenberger, Kevin M; Hughes, David H; Hughes, John P; Infante, Leopoldo; Irwin, Kent D; Jones, Andrew; Juin, Jean Baptiste; Klein, Jeff; Kosowsky, Arthur; Lau, Judy M; Limon, Michele; Lin, Yen-Ting; Lupton, Robert H; Marriage, Tobias A; Marsden, Danica; Martocci, Krista; Mauskopf, Phil; Menanteau, Felipe; Moodley, Kavilan; Moseley, Harvey; Netterfield, Calvin B; Niemack, Michael D; Nolta, Michael R; Page, Lyman A; Parker, Lucas; Partridge, Bruce; Reid, Beth; Sherwin, Blake D; Sievers, Jon; Spergel, David N; Staggs, Suzanne T; Swetz, Daniel S; Switzer, Eric R; Thornton, Robert; Tucker, Carole; Warne, Ryan; Wollack, Ed; Zhao, Yue
2010-01-01
We present constraints on cosmological parameters based on a sample of Sunyaev-Zel'dovich-selected galaxy clusters detected in a millimeter-wave survey by the Atacama Cosmology Telescope. The cluster sample used in this analysis consists of 9 optically-confirmed high-mass clusters comprising the high-significance end of the total cluster sample identified in 455 square degrees of sky surveyed during 2008 at 148 GHz. We focus on the most massive systems to reduce the degeneracy between unknown cluster astrophysics and cosmology derived from SZ surveys. We describe the scaling relation between cluster mass and SZ signal with a 4-parameter fit. Marginalizing over the values of the parameters in this fit with conservative priors gives sigma_8 = 0.851 +/- 0.115 and w = -1.14 +/- 0.35 for a spatially-flat wCDM cosmological model with WMAP 7-year priors on cosmological parameters. This gives a modest improvement in statistical uncertainty over WMAP 7-year constraints alone. Fixing the scaling relation between cluste...
Cosmology with Peculiar Velocities: Observational Effects
Andersen, P.; Davis, T. M.; Howlett, C.
2016-09-01
In this paper we investigate how observational effects could possibly bias cosmological inferences from peculiar velocity measurements. Specifically, we look at how bulk flow measurements are compared with theoretical predictions. Usually bulk flow calculations try to approximate the flow that would occur in a sphere around the observer. Using the Horizon Run 2 simulation we show that the traditional methods for bulk flow estimation can overestimate the magnitude of the bulk flow for two reasons: when the survey geometry is not spherical (the data do not cover the whole sky), and when the observations undersample the velocity distributions. Our results may explain why several bulk flow measurements found bulk flow velocities that seem larger than those expected in standard ΛCDM cosmologies. We recommend a different approach when comparing bulk flows to cosmological models, in which the theoretical prediction for each bulk flow measurement is calculated specifically for the geometry and sampling rate of that survey. This means that bulk flow values will not be comparable between surveys, but instead they are comparable with cosmological models, which is the more important measure.
Energy Technology Data Exchange (ETDEWEB)
NONE
2012-11-01
The report is an annual report of the Swedish CDM [Clean Development Mechanism] and JI [Joint Implementation]program for 2011. The report shows aims and goals of the business and the work of individual CDM and JI projects and multilateral funds which have been performed over the entire duration of life and especially during 2011. The report presents volume orders, deliveries of emission reduction units as well as the volumes expected to be needed for the fulfillment of the national target by 2020. The report also includes information about the average price for the emission reductions as well as alternative costs.
Cosmological evolution of a ghost scalar field
Sushkov, S. V.; Kim, S. -W
2004-01-01
We consider a scalar field with a negative kinetic term minimally coupled to gravity. We obtain an exact non-static spherically symmetric solution which describes a wormhole in cosmological setting. The wormhole is shown to connect two homogeneous spatially flat universes expanding with acceleration. Depending on the wormhole's mass parameter $m$ the acceleration can be constant (the de Sitter case) or infinitely growing.
A Comparative Analysis of the Supernova Legacy Survey Sample With ΛCDM and the Rh=ct Universe
Wei, Jun-Jie; Wu, Xue-Feng; Melia, Fulvio; Maier, Robert S.
2015-03-01
The use of Type Ia supernovae (SNe Ia) has thus far produced the most reliable measurement of the expansion history of the universe, suggesting that ΛCDM offers the best explanation for the redshift-luminosity distribution observed in these events. However, analysis of other kinds of sources, such as cosmic chronometers, gamma-ray bursts, and high-z quasars, conflicts with this conclusion, indicating instead that the constant expansion rate implied by the Rh = ct universe is a better fit to the data. The central difficulty with the use of SNe Ia as standard candles is that one must optimize three or four nuisance parameters characterizing supernova (SN) luminosities simultaneously with the parameters of an expansion model. Hence, in comparing competing models, one must reduce the data independently for each. We carry out such a comparison of ΛCDM and the Rh = ct universe using the SN Legacy Survey sample of 252 SN events, and show that each model fits its individually reduced data very well. However, since Rh = ct has only one free parameter (the Hubble constant), it follows from a standard model selection technique that it is to be preferred over ΛCDM, the minimalist version of which has three (the Hubble constant, the scaled matter density, and either the spatial curvature constant or the dark energy equation-of-state parameter). We estimate using the Bayes Information Criterion that in a pairwise comparison, the likelihood of Rh = ct is ˜90%, compared with only ˜10% for a minimalist form of ΛCDM, in which dark energy is simply a cosmological constant. Compared to Rh = ct, versions of the standard model with more elaborate parametrizations of dark energy are judged to be even less likely. This work is dedicated to the memory of Prof. Tan Lu, who sadly passed away 2014 December 3. Among his many achievements, he is considered to be one of the founders of high-energy astrophysics, and a pioneer in modern cosmology, in China.
Bulk viscous matter and recent acceleration of the universe
Energy Technology Data Exchange (ETDEWEB)
Sasidharan, Athira; Mathew, Titus K. [Cochin University of Science and Technology, Department of Physics, Kochi (India)
2015-07-15
We consider a cosmological model dominated by bulk viscous matter with a total bulk viscosity coefficient proportional to the velocity and acceleration of the expansion of the universe in such a way that ζ = ζ{sub 0} + ζ{sub 1}(a)/(a) + ζ{sub 2}(a)/(a). We show that there exist two limiting conditions in the bulk viscous coefficients (ζ{sub 0}, ζ{sub 1}, ζ{sub 2}) which correspond to a universe having a Big Bang at the origin, followed by an early decelerated epoch and then making a smooth transition into an accelerating epoch. We have constrained the model using the type Ia Supernovae data, evaluated the best estimated values of all the bulk viscous parameters and the Hubble parameter corresponding to the two limiting conditions. We found that even though the evolution of the cosmological parameters are in general different for the two limiting cases, they show identical behavior for the best estimated values of the parameters from both limiting conditions. A recent acceleration would occur if ζ{sub 0} + ζ{sub 1} > 1 for the first limiting conditions and if ζ{sub 0} + ζ{sub 1} < 1 for the second limiting conditions. The age of the universe predicted by this model is found to be less than that predicted from the oldest galactic globular clusters. The total bulk viscosity seems to be negative in the past and becomes positive when z ≤ 0.8. So the model violates the local second law of thermodynamics. However, the model satisfies the generalized second law of thermodynamics at the apparent horizon throughout the evolution of the universe. We also made a statefinder analysis of the model and found that it is distinguishably different from the standard ΛCDM model at present, but it shows a de Sitter type behavior in the far future of the evolution. (orig.)
A look to nonlinear interacting Ghost dark energy cosmology
Khurshudyan, Martiros
2016-07-01
In this paper, we organize a look to nonlinear interacting Ghost dark energy cosmology involving a discussion on the thermodynamics of the Ghost dark energy, when the universe is bounded via the Hubble horizon. One of the ways to study a dark energy model, is to reconstruct thermodynamics of it. Ghost dark energy is one of the models of the dark energy which has an explicitly given energy density as a function of the Hubble parameter. There is an active discussion towards various cosmological scenarios, where the Ghost dark energy interacts with the pressureless cold dark matter (CDM). Recently, various models of the varying Ghost dark energy has been suggested, too. To have a comprehensive understanding of suggested models, we will discuss behavior of the cosmological parameters on parameter-redshift z plane. Some discussion on Om and statefinder hierarchy analysis of these models is presented. Moreover, up to our knowledge, suggested forms of interaction between the Ghost dark energy and cold dark matter (CDM) are new, therefore, within obtained results, we provide new contribution to previously discussed models available in the literature. Our study demonstrates that the forms of the interactions considered in the Ghost dark energy cosmology are not exotic and the justification of this is due to the recent observational data.
Testing Cosmological Models with Type Ic Super Luminous Supernovae
Wei, Jun-Jie; Melia, Fulvio
2015-01-01
The use of type Ic Super Luminous Supernovae (SLSN Ic) to examine the cosmological expansion introduces a new standard ruler with which to test theoretical models. The sample suitable for this kind of work now includes 11 SLSNe Ic, which have thus far been used solely in tests involving $\\Lambda$CDM. In this paper, we broaden the base of support for this new, important cosmic probe by using these observations to carry out a one-on-one comparison between the $R_{\\rm h}=ct$ and $\\Lambda$CDM cosmologies. We individually optimize the parameters in each cosmological model by minimizing the $\\chi^{2}$ statistic. We also carry out Monte Carlo simulations based on these current SLSN Ic measurements to estimate how large the sample would have to be in order to rule out either model at a $\\sim 99.7\\%$ confidence level. The currently available sample indicates a likelihood of $\\sim$$70-80\\%$ that the $R_{\\rm h}=ct$ Universe is the correct cosmology versus $\\sim$$20-30\\%$ for the standard model. These results are suggest...
Agegraphic dark energy: growth index and cosmological implications
Malekjani, M; Davari, Z; Mehrabi, A; Rezaei, M
2016-01-01
We study the main cosmological properties of the agegraphic dark energy model at the expansion and perturbation levels. Initially, using the latest cosmological data we implement a joint likelihood analysis in order to constrain the cosmological parameters. Then we test the performance of the agegraphic dark energy model at the perturbation level and we define its difference from the usual $\\Lambda$CDM model. Within this context, we verify that the growth index of matter fluctuations depends on the choice of the considered agegraphic dark energy (homogeneous or clustered). In particular, assuming a homogeneous agegraphic dark energy we find, for the first time, that the asymptotic value of the growth index is $\\gamma \\approx 5/9$, which is close to that of the usual $\\Lambda$ cosmology, $\\gamma^{(\\Lambda)} \\approx 6/11$. Finally, if the distribution of dark energy is clustered then we obtain $\\gamma \\approx 1/2$ which is $\\sim 8\\%$ smaller than that of the $\\Lambda$CDM model.
A Reformed CDM - including new mechanisms for sustainable development
Energy Technology Data Exchange (ETDEWEB)
Holm Olsen, K.; Fenhann, J.
2009-07-01
The annual CD4CDM Perspectives Series features a topic of pivotal importance to the global carbon market. The series seeks to communicate the diverse insights and visions of leading actors in the carbon market to better inform the decisions of professionals and policymakers in developing countries. The second theme of the series focuses on how the CDM can be reformed in a post-2012 climate regime, including new mechanism for sustainable development. Seventeen contributors from the private sector, Designated National Authorities, the Executive Board, research, and development agencies present their perspective on meeting challenges such as the unequal regional distribution of CDM projects, concerns about environmental integrity and technology transfer, complex governance procedures, and questions about the CDM's contribution to sustainable development. The new ideas and solutions to these challenges proposed by the authors in this edition of Perspectives have been solicited to help professionals and policy makers make the best decisions in the lead-up to COP 15 in Copenhagen and beyond. (au)
Wind farm investment risks under uncertain CDM benefit in China
International Nuclear Information System (INIS)
China has set an ambitious target to increase its wind power capacity by 35 GW from 2007 to 2020. The country's hunger for clean power provides great opportunities for wind energy investors. However, risks from China's uncertain electricity market regulation and an uncertain energy policy framework, mainly due to uncertain Clean Development Mechanism (CDM) benefits, prevent foreign investors from investing in China's wind energy. The objectives of this paper are to: (1) quantify wind energy investment risk premiums in an uncertain international energy policy context and (2) evaluate the impact of uncertain CDM benefits on the net present values of wind power projects. With four scenarios, this study simulates possible prices of certified emissions reductions (CERs) from wind power projects. Project net present values (NPVs) have been calculated. The project risk premiums are drawn from different and uncertain CER prices. Our key findings show that uncertain CDM benefits will significantly affect the project NPVs. This paper concludes that the Chinese government needs revising its tariff incentives, most likely by introducing fixed feed-in tariffs (FITs), and re-examining its CDM-granting policy and its wind project tax rates, to facilitate wind power development and enable China to achieve its wind energy target.
How to attribute market leakage to CDM projects
Vöhringer, F.; Kuosmanen, T.K.; Dellink, R.B.
2006-01-01
Economic studies suggest that market leakage rates of greenhouse gas abatement can reach the two-digit percentage range. Although the Marrakesh Accords require Clean Development Mechanism (CDM) projects to account for leakage, most projects neglect market leakage. Insufficient leakage accounting is
CDM: Teaching Discrete Mathematics to Computer Science Majors
Sutner, Klaus
2005-01-01
CDM, for computational discrete mathematics, is a course that attempts to teach a number of topics in discrete mathematics to computer science majors. The course abandons the classical definition-theorem-proof model, and instead relies heavily on computation as a source of motivation and also for experimentation and illustration. The emphasis on…
Brandenberger, Robert H.
2008-01-01
String gas cosmology is a string theory-based approach to early universe cosmology which is based on making use of robust features of string theory such as the existence of new states and new symmetries. A first goal of string gas cosmology is to understand how string theory can effect the earliest moments of cosmology before the effective field theory approach which underlies standard and inflationary cosmology becomes valid. String gas cosmology may also provide an alternative to the curren...
Self-acceleration and matter content in bicosmology from Noether Symmetries
Bouhmadi-López, Mariam; Martín-Moruno, Prado
2016-01-01
We consider the existence of Noether symmetries in bigravity cosmologies in order to constrain the material content minimally coupled to the gravitational sector that we are not inhabiting. Interestingly, a Noether symmetry not only constrain the matter content of the universe we do not inhabit but also comes as a sort of bonus on the form of a very interesting dynamics of the universe we live in. In fact, by assuming that our universe is filled with standard matter and radiation, we show that the existence of a Noether symmetry implies the existence of a vacuum energy in our universe that can explain, in a natural way, the current acceleration of the universe. This vacuum energy is intrinsic to the model and can be realized either for a theory that is not properly a bigravity model or for a genuinely bimetric scenario. In fact, it would correspond to a "mono"-universe with a $\\Lambda$CDM matter symmetry or to a bimetric world where our universe would have once again a $\\Lambda$CDM matter symmetry while the n...
Religion, theology and cosmology
Directory of Open Access Journals (Sweden)
John T. Fitzgerald
2013-10-01
Full Text Available Cosmology is one of the predominant research areas of the contemporary world. Advances in modern cosmology have prompted renewed interest in the intersections between religion, theology and cosmology. This article, which is intended as a brief introduction to the series of studies on theological cosmology in this journal, identifies three general areas of theological interest stemming from the modern scientific study of cosmology: contemporary theology and ethics; cosmology and world religions; and ancient cosmologies. These intersections raise important questions about the relationship of religion and cosmology, which has recently been addressed by William Scott Green and is the focus of the final portion of the article.
Boeyens, Jan CA
2010-01-01
The composition of the most remote objects brought into view by the Hubble telescope can no longer be reconciled with the nucleogenesis of standard cosmology and the alternative explanation, in terms of the LAMBDA-Cold-Dark-Matter model, has no recognizable chemical basis. A more rational scheme, based on the chemistry and periodicity of atomic matter, opens up an exciting new interpretation of the cosmos in terms of projective geometry and general relativity. The response of atomic structure to environmental pressure predicts non-Doppler cosmical redshifts and equilibrium nucleogenesis by alp
Fabris, J C; Rodrigues, D C; Batista, C E M; Daouda, M H
2012-01-01
We review the difficulties of the generalized Chaplygin gas model to fit observational data, due to the tension between background and perturbative tests. We argue that such issues may be circumvented by means of a self-interacting scalar field representation of the model. However, this proposal seems to be successful only if the self-interacting scalar field has a non-canonical form. The latter can be implemented in Rastall's theory of gravity, which is based on a modification of the usual matter conservation law. We show that, besides its application to the generalized Chaplygin gas model, other cosmological models based on Rastall's theory have many interesting and unexpected new features.
Bardeen, J. M.
The last several years have seen a tremendous ferment of activity in astrophysical cosmology. Much of the theoretical impetus has come from particle physics theories of the early universe and candidates for dark matter, but what promise to be even more significant are improved direct observations of high z galaxies and intergalactic matter, deeper and more comprehensive redshift surveys, and the increasing power of computer simulations of the dynamical evolution of large scale structure. Upper limits on the anisotropy of the microwave background radiation are gradually getting tighter and constraining more severely theoretical scenarios for the evolution of the universe.
Brane Cosmology and Higher Derivative Theory
Naboulsi, R
2003-01-01
In this paper, we have considered a cosmological model with density perturbation and decreasing cosmological constant of the form Lambda = 3beta (frac{dot{R}^2}{R^2}) + delta (frac{ddot{R}}{R}), beta, gamma = const. Inspired from brane cosmology, we supposed the presence of exotic density related to the cosmological constant by the formula 2Lambda = 3m^2, where m is a constant having the dimension of Hubble constant. Their effects on the evolution of the spatially, flat FRW cosmoligical model of the Universe is analyzed in the framework of higher derivative theory. The Universe is found to be accelerating with time with no initial singularity for beta < frac{1}{3} and the cosmological constant is found to decrease as t^{-2} but smaller than 3H^2. The presence of interacting scalar field is also discussed.
Cosmological constraints on a classical limit of quantum gravity
Easson, D A; Trodden, M; Wohlfarth, M N R; Easson, Damien A.; Schuller, Frederic P.; Trodden, Mark; Wohlfarth, Mattias N.R.
2005-01-01
We investigate the cosmology of a recently proposed deformation of Einstein gravity, emerging from quantum gravity heuristics. The theory is constructed to have de Sitter space as a vacuum solution, and thus to be relevant to the accelerating universe. However, this solution turns out to be unstable, and the true phase space of cosmological solutions is significantly more complex, displaying two late-time power-law attractors -- one accelerating and the other dramatically decelerating. It is also shown that non-accelerating cosmologies sit on a separatrix between the two basins of attraction of these attractors. Hence it is impossible to pass from a decelerating cosmology to an accelerating one, as required in standard cosmology for consistency with nucleosynthesis and structure formation and compatibility with the data inferred from supernovae Ia. We point out that alternative models of the early universe, such as the one investigated here might provide possible ways to circumvent these requirements.
Energy Technology Data Exchange (ETDEWEB)
Heitmann, Katrin [Los Alamos National Laboratory; Habib, Salman [Los Alamos National Laboratory; Higdon, David [Los Alamos National Laboratory; Williams, Brian J [Los Alamos National Laboratory; White, Martin [Los Alamos National Laboratory; Wagner, Christian [Los Alamos National Laboratory
2008-01-01
The power spectrum of density fluctuations is a foundational source of cosmological information. Precision cosmological probes targeted primarily at investigations of dark energy require accurate theoretical determinations of the power spectrum in the nonlinear regime. To exploit the observational power of future cosmological surveys, accuracy demands on the theory are at the one percent level or better. Numerical simulations are currently the only way to produce sufficiently error-controlled predictions for the power spectrum. The very high computational cost of (precision) N-body simulations is a major obstacle to obtaining predictions in the nonlinear regime, while scanning over cosmological parameters. Near-future observations, however, are likely to provide a meaningful constraint only on constant dark energy equation of state 'wCDM' cosmologies. In this paper we demonstrate that a limited set of only 37 cosmological models -- the 'Coyote Universe' suite -- can be used to predict the nonlinear matter power spectrum at the required accuracy over a prior parameter range set by cosmic microwave background observations. This paper is the second in a series of three, with the final aim to provide a high-accuracy prediction scheme for the nonlinear matter power spectrum for wCDM cosmologies.
Heitmann, Katrin; Higdon, David; White, Martin; Habib, Salman; Williams, Brian J.; Lawrence, Earl; Wagner, Christian
2009-11-01
The power spectrum of density fluctuations is a foundational source of cosmological information. Precision cosmological probes targeted primarily at investigations of dark energy require accurate theoretical determinations of the power spectrum in the nonlinear regime. To exploit the observational power of future cosmological surveys, accuracy demands on the theory are at the 1% level or better. Numerical simulations are currently the only way to produce sufficiently error-controlled predictions for the power spectrum. The very high computational cost of (precision) N-body simulations is a major obstacle to obtaining predictions in the nonlinear regime, while scanning over cosmological parameters. Near-future observations, however, are likely to provide a meaningful constraint only on constant dark energy equation of state, "wCDM", cosmologies. In this paper, we demonstrate that a limited set of only 37 cosmological models—the "Coyote Universe" suite—can be used to predict the nonlinear matter power spectrum to 1% over a prior parameter range set by current cosmic microwave background observations. This paper is the second in a series of three, with the final aim to provide a high-accuracy prediction scheme for the nonlinear matter power spectrum for wCDM cosmologies.
Carbon emission right as a new property right: rescue CDM developers in China from 2012
Pei, Q; Liu, L.; Zhang, DD
2012-01-01
Clean development mechanism (CDM) is encountering many uncertainties due to the coming end of the commitment period and critically suggested reformation. As the largest participant in the CDM market, China shoulders the biggest proportion of market risk. Among the studies on CDM in China, few have focused upon the legal aspect of CDM, which is crucial in defending developers’ interests. To fill this research gap in making the transition from policy to law, this paper claims that carbon emissi...
Cosmological Models and Renormalization Group Flow
Kristjansson, K R
2002-01-01
We study cosmological solutions of Einstein gravity with a positive cosmological constant and perfect fluid matter in diverse dimensions. These include big-bang models that re-collaspse, big-bang models that approach de Sitter acceleration at late times, and bounce models that are both past and future asymptotically de Sitter. The re-collapsing and the bounce geometries are all tall in the sense that entire spatial slices become visible to a comoving observer before the end of conformal time, while the accelerating big-bang geometries can be either short or tall. We consider the interpretation of these cosmological solutions as renormalization group flows in a dual field theory and give a geometric interpretation of the associated c-function as the area of the apparent cosmological horizon in Planck units. We find that the covariant entropy bound is violated in certain of our solutions and thus holography may be used to restrict the model parameters.
The case for the cosmological constant
Indian Academy of Sciences (India)
Varun Sahni
2000-07-01
I present a short overview of current observational results and theoretical models for a cosmological constant. The main motivation for invoking a small cosmological constant (or -term) at the present epoch has to do with observations of high redshift Type Ia supernovae which suggest an accelerating universe. A ﬂat accelerating universe is strongly favoured by combining supernovae observations with observations of CMB anisotropies on degree scales which give the `best-ﬁt’ values ≃ 0.7 and m ≃ 0.3. A time dependent cosmological -term can be generated by scalar ﬁeld models with exponential and power law potentials. Some of these models can alleviate the `ﬁne tuning’ problem which faces the cosmological constant.
Dark Energy, Particle Physics and Cosmology
Turner, Michael S.
2012-05-01
Dark energy and cosmic acceleration is one of the three pillars of the current cosmological paradigm. Moreover, both raise fundamental issues in cosmology and particle physics. In particle physics, the dark energy problem is intimately related to the perplexing issue of why the quantum energy of the vacuum is so small. In cosmology, the nature of the dark energy is crucial to understanding the destiny of the Universe. I will discuss the status of current models for dark energy -- including vacuum energy and rolling scalar fields -- their implications for cosmology and for particle physics and how they can be tested by WFIRST. I will also address the status of the possibility that cosmic acceleration is explained by modifying or replacing general relativity.
Hinterbichler, Kurt; Levy, Aaron; Matas, Andrew
2011-01-01
The symmetron is a scalar field associated with the dark sector whose coupling to matter depends on the ambient matter density. The symmetron is decoupled and screened in regions of high density, thereby satisfying local constraints from tests of gravity, but couples with gravitational strength in regions of low density, such as the cosmos. In this paper we derive the cosmological expansion history in the presence of a symmetron field, tracking the evolution through the inflationary, radiation- and matter-dominated epochs, using a combination of analytical approximations and numerical integration. For a broad range of initial conditions at the onset of inflation, the scalar field reaches its symmetry-breaking vacuum by the present epoch, as assumed in the local analysis of spherically-symmetric solutions and tests of gravity. For the simplest form of the potential, the energy scale is too small for the symmetron to act as dark energy, hence we must add a cosmological constant to drive late-time cosmic acceler...
The Learning Process and Technological Change in Wind Power: Evidence from China's CDM Wind Projects
Tang, Tian; Popp, David
2016-01-01
The Clean Development Mechanism (CDM) is a project-based carbon trade mechanism that subsidizes the users of climate-friendly technologies and encourages technology transfer. The CDM has provided financial support for a large share of Chinese wind projects since 2002. Using pooled cross-sectional data of 486 registered CDM wind projects in China…
Supporting Open Access to European Academic Courses: The ASK-CDM-ECTS Tool
Sampson, Demetrios G.; Zervas, Panagiotis
2013-01-01
Purpose: This paper aims to present and evaluate a web-based tool, namely ASK-CDM-ECTS, which facilitates authoring and publishing on the web descriptions of (open) academic courses in machine-readable format using an application profile of the Course Description Metadata (CDM) specification, namely CDM-ECTS. Design/methodology/approach: The paper…
Newtonian cosmology - Problems of cosmological didactics
Energy Technology Data Exchange (ETDEWEB)
Skarzynski, E.
1983-03-01
The article presents different methods of model construction in Newtonian cosmology. Newtonian cosmology is very convenient for discussion of local problems, so the problems presented are of great didactic importance. The constant k receives a new interpretation in relativistic cosmology as the curvature of the space in consequence of the greater informational capacity of Riemann space in comparison to Euclidean space. 11 references.
Off-shell Dark Matter: A Cosmological relic of Quantum Gravity
Saravani, Mehdi; Afshordi, Niayesh
2016-01-01
We study a novel proposal for the origin of cosmological cold dark matter (CDM) which is rooted in the quantum nature of spacetime. In this model, off-shell modes of quantum fields can exist in asymptotic states as a result of spacetime nonlocality (expected in generic theories of quantum gravity), and play the role of CDM, which we dub off-shell dark matter (OfDM). However, their rate of production is suppressed by the scale of non-locality (e.g. Planck length). As a result, we show that OfD...
DM haloes in the fifth-force cosmology
International Nuclear Information System (INIS)
We investigate how long-range scalar interactions affect the properties of dark matter haloes. For doing so we employ the ReBEL model which implements an additional interaction between dark matter particles. On the phenomenological level this is equivalent to a modification of gravity. We analyse the differences between five ReBEL models and ΛCDM using a series of high resolution cosmological simulations. Emphasis is placed on investigating how halo properties change in the presence of a fifth force. We report that the density profile of ReBEL haloes is well described by the NFW profile but with mean concentrations from 5% to a few times higher than the standard ΛCDM value. We also find a slight increase of the halo spin for haloes more massive than 5 × 1011M☉, reflecting a higher rotational support of those haloes due to scalar forces. In addition, the dark matter haloes in our models are more spherical than their counterparts in ΛCDM. The ReBEL haloes are also more virialised, with a large difference from ΛCDM for strong fifth forces and a much smaller change for weak scalar interactions
Directory of Open Access Journals (Sweden)
Pierre-Henri Chavanis
2013-01-01
Full Text Available We consider a cosmological model based on a quadratic equation of state (where is the Planck density and is the cosmological density “unifying” vacuum energy, radiation, and dark energy. For , it reduces to leading to a phase of early accelerated expansion (early inflation with a constant density equal to the Planck density g/m3 (vacuum energy. For , we recover the equation of state of radiation . For , we get leading to a phase of late accelerated expansion (late inflation with a constant density equal to the cosmological density g/m3 (dark energy. The temperature is determined by a generalized Stefan-Boltzmann law. We show a nice “symmetry” between the early universe (vacuum energy + radiation and the late universe (radiation + dark energy. In our model, they are described by two polytropic equations of state with index and respectively. Furthermore, the Planck density in the early universe plays a role similar to that of the cosmological density in the late universe. They represent fundamental upper and lower density bounds differing by 122 orders of magnitude. We add the contribution of baryonic matter and dark matter considered as independent species and obtain a simple cosmological model describing the whole evolution of the universe. We study the evolution of the scale factor, density, and temperature. This model gives the same results as the standard CDM model for , where is the Planck time and completes it by incorporating the phase of early inflation in a natural manner. Furthermore, this model does not present any singularity at and exists eternally in the past (although it may be incorrect to extrapolate the solution to the infinite past. Our study suggests that vacuum energy, radiation, and dark energy may be the manifestation of a unique form of “generalized radiation.” By contrast, the baryonic and dark matter components of the universe are treated as different species. This is at variance with usual models
Disappearing cosmological constant in f(R) gravity
Starobinsky, Alexei A
2007-01-01
For higher-derivative f(R) gravity where R is the Ricci scalar, a class of models is proposed which produce viable cosmology different from the LambdaCDM one at recent times and satisfy cosmological, Solar system and laboratory tests. These models have both flat and de Sitter space-times as particular solutions in the absence of matter. Thus, a cosmological constant is zero in flat space-time, but appears effectively in a curved one for sufficiently large R. A 'smoking gun' for these models would be small discrepancy in values of the slope of the primordial perturbation power spectrum determined from galaxy surveys and CMB fluctuations. On the other hand, a new problem for dark energy models based on f(R) gravity is pointed which is connected with possible overproduction of new massive scalar particles (scalarons) arising in this theory in the very early Universe.
Observational constraints on undulant cosmologies
Energy Technology Data Exchange (ETDEWEB)
Barenboim, Gabriela; /Valencia U.; Mena Requejo, Olga; Quigg, Chris; /Fermilab
2005-10-01
In an undulant universe, cosmic expansion is characterized by alternating periods of acceleration and deceleration. We examine cosmologies in which the dark-energy equation of state varies periodically with the number of e-foldings of the scale factor of the universe, and use observations to constrain the frequency of oscillation. We find a tension between a forceful response to the cosmic coincidence problem and the standard treatment of structure formation.
Alfaro, Jorge; González, Pablo
2012-01-01
We present a model of the gravitational field based on two symmetric tensors. Gravity is affected by the new field, but outside matter the predictions of the model coincide exactly with general relativity, so all classical tests are satisfied. We find that massive particles do not follow a geodesic while massless particles trajectories are null geodesics of an effective metric. We study the Cosmological case, where we get an accelerated expansion of the universe without dark energy. We also i...
Latin America-Alberta-Canada CDM Conference: Conference Summary
International Nuclear Information System (INIS)
Proposals for joint initiatives put forward by participants at the Clean Development Mechanisms Conference included (1) the development of regional guidelines to assist governments in setting regulatory framework for projects to qualify as CDMs, (2) development of regional baselines and regional performance indicators for social benefit and sustainable development, (3) a specific project in Mexico to test the CDM framework and eligibility criteria, (4) development of bilateral agreements between governments, (5) staff exchanges between associations and governments, (6) government recognition for private sector actions such as a letter affirming that certified emission reductions would be accepted for commitments, (7) sharing of information on websites, and (8) capacity building, training programs and workshops. The Conference also identified common ground and shared interest in CDM initiatives among participants, and readiness to explore joint ventures and technology transfer opportunities. There is wide-spread agreement on the need to resolve uncertainties of CDM, such as baseline and additionality; monitoring, reporting, certification; buyer/seller liability; adaptation levy for international emissions trading, joint implementation and clean development mechanism transactions. Significant consensus exists regarding benefits of 'learning by doing' and the need for minimizing transaction costs and risks. Baseline and Additionality are recognized as the critical issues, with social benefits, sustainable development aspects of projects, and the critical nature of integrity, technical expertise, and track record of both partners as close seconds. The importance of framework arrangements, host country approval, clear designation of responsibility and authority to approve projects, the need for specific guidelines and specific approval procedures, country-to-country agreements and national crediting arrangement are recognized by all participants. With regard to issues
TESTING NONSTANDARD COSMOLOGICAL MODELS WITH SNLS3 SUPERNOVA DATA AND OTHER COSMOLOGICAL PROBES
Energy Technology Data Exchange (ETDEWEB)
Li Zhengxiang; Yu Hongwei [Department of Physics and Key Laboratory of Low Dimensional Quantum Structures and Quantum Control of the Ministry of Education, Hunan Normal University, Changsha, Hunan 410081 (China); Wu Puxun, E-mail: hwyu@hunnu.edu.cn [Center of Nonlinear Science and Department of Physics, Ningbo University, Ningbo, Zhejiang 315211 (China)
2012-01-10
We investigate the implications for some nonstandard cosmological models using data from the first three years of the Supernova Legacy Survey (SNLS3), assuming a spatially flat universe. A comparison between the constraints from the SNLS3 and those from other SN Ia samples, such as the ESSENCE, Union2, SDSS-II, and Constitution samples, is given and the effects of different light-curve fitters are considered. We find that analyzing SNe Ia with SALT2 or SALT or SiFTO can give consistent results and the tensions between different data sets and different light-curve fitters are obvious for fewer-free-parameters models. At the same time, we also study the constraints from SNLS3 along with data from the cosmic microwave background and the baryonic acoustic oscillations (CMB/BAO), and the latest Hubble parameter versus redshift (H(z)). Using model selection criteria such as {chi}{sup 2}/dof, goodness of fit, Akaike information criterion, and Bayesian information criterion, we find that, among all the cosmological models considered here ({Lambda}CDM, constant w, varying w, Dvali-Gabadadze-Porrati (DGP), modified polytropic Cardassian, and the generalized Chaplygin gas), the flat DGP is favored by SNLS3 alone. However, when additional CMB/BAO or H(z) constraints are included, this is no longer the case, and the flat {Lambda}CDM becomes preferred.
On the luminosity distance and the epoch of acceleration
Sutherland, Will
2015-01-01
Standard cosmological models based on general relativity (GR) with dark energy predict that the Universe underwent a transition from decelerating to accelerating expansion at a moderate redshift $z_{acc} \\sim 0.7$. Clearly, it is of great interest to directly measure this transition in a model-independent way, without the assumption that GR is the correct theory of gravity. We explore to what extent supernova (SN) luminosity distance measurements provide evidence for such a transition: we show that, contrary to intuition, the well-known "turnover" in the SN distance residuals $\\Delta\\mu$ relative to an empty (Milne) model does not give firm evidence for such a transition within the redshift range spanned by SN data. The observed turnover in that diagram is predominantly due to the negative curvature in the Milne model, {\\em not} the deceleration predicted by $\\Lambda$CDM and relatives. We show that there are several advantages in plotting distance residuals against a flat, non-accelerating model $(w = -1/3)$,...
f(R,T,R{sub μν}T{sup μν}) gravity phenomenology and ΛCDM universe
Energy Technology Data Exchange (ETDEWEB)
Odintsov, Sergei D., E-mail: odintsov@ieec.uab.es [Instituciò Catalana de Recerca i Estudis Avançats (ICREA), Barcelona (Spain); Institut de Ciències de l' Espai ICE (CSIC-IEEC), Campus UAB Facultat de Ciències, Torre C5-Parell-2a pl, E-08193 Bellaterra (Barcelona) (Spain); Sáez-Gómez, Diego, E-mail: diego.saezgomez@uct.ac.za [Astrophysics, Cosmology and Gravity Centre (ACGC) and Department of Mathematics and Applied Mathematics, University of Cape Town, Rondebosch 7701, Cape Town (South Africa); Fisika Teorikoaren eta Zientziaren Historia Saila, Zientzia eta Teknologia Fakultatea, Euskal Herriko Unibertsitatea, 644 Posta Kutxatila, 48080 Bilbao (Spain)
2013-10-01
We propose general f(R,T,R{sub μν}T{sup μν}) theory as generalization of covariant Hořava-like gravity with dynamical Lorentz symmetry breaking. FRLW cosmological dynamics for several versions of such theory is considered. The reconstruction of the above action is explicitly done, including the numerical reconstruction for the occurrence of ΛCDM universe. De Sitter universe solutions in the presence of non-constant fluid are also presented. The problem of matter instability in f(R,T,R{sub μν}T{sup μν}) gravity is discussed.
Giallongo, E.; Menci, N.; Fiore, F.; Castellano, M.; Fontana, A.; Grazian, A.; Pentericci, L
2012-01-01
We have evaluated the contribution of the AGN population to the ionization history of the Universe based on a semi-analytic model of galaxy formation and evolution in the CDM cosmological scenario. The model connects the growth of black holes and of the ensuing AGN activity to galaxy interactions. In the model we have included a self consistent physical description of the escape of ionizing UV photons; this is based on the blast-wave model for the AGN feedback we developed in a previous paper...
Negative Energy Cosmology and the Cosmological Constant
Prokopec, Tomislav
2011-01-01
It is well known that string theories naturally compactify on anti-de Sitter spaces, and yet cosmological observations show no evidence of a negative cosmological constant in the early Universe's evolution. In this letter we present two simple nonlocal modifications of the standard Friedmann cosmology that can lead to observationally viable cosmologies with an initial (negative) cosmological constant. The nonlocal operators we include are toy models for the quantum cosmological backreaction. In Model I an initial quasiperiodic oscillatory epoch is followed by inflation and a late time matter era, representing a dark matter candidate. The backreaction in Model II quickly compensates the negative cosmological term such that the Ricci curvature scalar rapidly approaches zero, and the Universe ends up in a late time radiation era.
The low-mass end of the neutral gas mass and velocity width functions of galaxies in ΛCDM
Yaryura, C. Y.; Helmi, A.; Abadi, M. G.; Starkenburg, E.
2016-04-01
We use the high-resolution Aquarius cosmological dark matter simulations coupled to the semi-analytic model by Starkenburg et al. to study the H I content and velocity width properties of field galaxies at the low-mass end in the context of Λ cold dark matter (ΛCDM). We compare our predictions to the observed Arecibo Legacy Fast ALFA (ALFALFA) survey H I mass and velocity width functions, and find very good agreement without fine-tuning, when considering central galaxies. Furthermore, the properties of the dark matter haloes hosting galaxies, characterized by their peak velocity and circular velocity at two radial disc scalelengths overlap perfectly with the inferred values from observations. This suggests that our galaxies are placed in the right dark matter haloes, and consequently at face value, we do not find any discrepancy with the predictions from the ΛCDM model. Our analysis indicates that previous tensions, apparent when using abundance matching models, arise because this technique cannot be straightforwardly applied for objects with masses Mvir < 1010M⊙.
Project Boundary Setting and Leakage Treatment in CDM Project
Institute of Scientific and Technical Information of China (English)
ZOU Chen; WANG Shujuan; DUAN Maosheng; CHEN Changhe
2005-01-01
Project boundary setting and leakage treatment are two important issues to be considered when a clean development mechanism (CDM) project is being designed. There are still many uncertainties concerning these two issues. This paper reviews the concepts of project boundary setting and leakage in CDM projects, cites the types and sources of leakage, discusses the principles for determining leakage, and gives some proposed methods for dealing with leakage. A case study, using several steps to solve the boundary and leakage problems,shows how the analyzed principles and treatments can be implemented in a real project. Based on the result of the case study, the methods discussed are shown to be appropriate for settling leakage issues.
An improved cosmological model fitting of Planck data with a dark energy spike
Park, Chan-Gyung
2015-01-01
The $\\Lambda$ cold dark matter ($\\Lambda\\textrm{CDM}$) model is currently known as the simplest cosmology model that best describes observations with minimal number of parameters. Here we introduce a cosmology model that is preferred over the conventional $\\Lambda\\textrm{CDM}$ one by constructing dark energy as the sum of the cosmological constant $\\Lambda$ and the additional fluid that is designed to have an extremely short transient spike in energy density during the radiation-matter equality era and the early scaling behavior with radiation and matter densities. The density parameter of the additional fluid is defined as a Gaussian function plus a constant in logarithmic scale-factor space. Searching for the best-fit cosmological parameters in the presence of such a dark energy spike gives a far smaller chi-square value by about five times the number of additional parameters introduced and narrower constraints on matter density and Hubble constant compared with the best-fit $\\Lambda\\textrm{CDM}$ model. The...
Vankov, A
1998-01-01
The suggested alternative cosmology is based on the idea of barion symmetric universe, in which our home universe is a representative of multitude of typical matter and antimatter universes. This alternative concept gives a physically reasonable explanation of all major problems of the Standard Cosmological Model. Classification Code MSC: Cosmology 524.8 Key words: standard cosmological model, alternative cosmology, barionic symmetry, typical universe, quasars, cosmic rays.
Estimating the CDM market under the Bonn Agreement
Jotzo, Frank; Michaelowa, Axel
2001-01-01
We analyse the impact of the agreement on implementation of the Kyoto Protocol achieved at COP6bis in Bonn in July 2001 on investment in greenhouse gas emission reduction projects in developing countries through the Clean Development Mechanism (CDM). The required actual emission reductions for participating Annex B countries overall will be relatively small, as the United States do not intend to ratify the Protocol and significant amounts of carbon sequestered in domestic sinks will be credit...
Constraints on holographic cosmologies from strong lensing systems
International Nuclear Information System (INIS)
We use strongly gravitationally lensed (SGL) systems to put additional constraints on a set of holographic dark energy models. Data available in the literature (redshift and velocity dispersion) is used to obtain the Einstein radius and compare it with model predictions. We found that the ΛCDM is the best fit to the data. Although a preliminary statistical analysis seems to indicate that two of the holographic models studied show interesting agreement with observations, a stringent test lead us to the result that neither of the holographic models are competitive with the ΛCDM. These results highlight the importance of Strong Lensing measurements to provide additional observational constraints to alternative cosmological models, which are necessary to shed some light into the dark universe
Redshift drift in varying speed of light cosmology
International Nuclear Information System (INIS)
We derive a redshift drift formula within the framework of varying speed of light (VSL) theory using the specific ansatz for the variability of c(t)=c0an(t). We show that negative values of the parameter n, which correspond to diminishing value of the speed of light during the evolution of the universe, effectively rescale dust matter to become little negative pressure matter, and the cosmological constant to became phantom. Positive values of n (growing c(t)) make VSL model to become more like Cold Dark Matter (CDM) model. Observationally, there is a distinction between the VSL model and the ΛCDM model for the admissible values of the parameter n∼−10−5, though it will be rather difficult to detect by planned extremely large telescopes (EELT, TMT, GMT) within their accuracy
Economic Impact of CDM Implementation through Alternate Energy Resource Substitution
Directory of Open Access Journals (Sweden)
K.J. Sreekanth
2013-02-01
Full Text Available Since the Kyoto protocol agreement, Clean Development Mechanism (CDM hasgarnered large emphasis in terms of certified emission reductions (CER not only amidst the globalcarbon market but also in India. This paper attempts to assess the impact of CDM towardssustainable development particularly in rural domestic utility sector that mainly includes lightingand cooking applications, with electricity as the source of energy. A detailed survey has undertakenin the state of Kerala, in southern part of India to study the rural domestic energy consumptionpattern. The data collected was analyzed that throws insight into the interrelationships of thevarious parameters that influence domestic utility sector pertaining to energy consumption byusing electricity as the source of energy. The interrelationships between the different parameterswere modeled that optimizes the contribution of electricity on domestic utility sector. The resultswere used to estimate the feasible extent of CO2 emission reduction through use of electricity as theenergy resources, vis-à-vis its economic viability through cost effectiveness. The analysis alsoprovides a platform for implementing CDM projects in the sector and related prospects withrespects to the Indian scenario.
Ignat'ev, Yurii
2016-01-01
On the basis of qualitative analysis of the system of differential equations of the standard cosmological model it is shown that in the case of zero cosmological constant this system has a stable center corresponding to zero values of potential and its derivative at infinity. Thus, the cosmological model based on single massive classical scalar field in infinite future would give a flat Universe. The carried out numerical simulation of the dynamic system corresponding to the system of Einstein - Klein - Gordon equations showed that at great times of the evolution the invariant cosmological acceleration has an oscillating character and changes from $-2$ (braking), to $+1$ (acceleration). Average value of the cosmological acceleration is negative and is equal to $-1/2$. Oscillations of the cosmological acceleration happen on the background of rapidly falling Hubble constant. In the case of nonzero value of the cosmological constant depending on its value there are possible three various qualitative behavior typ...
Averaging anisotropic cosmologies
International Nuclear Information System (INIS)
We examine the effects of spatial inhomogeneities on irrotational anisotropic cosmologies by looking at the average properties of anisotropic pressure-free models. Adopting the Buchert scheme, we recast the averaged scalar equations in Bianchi-type form and close the standard system by introducing a propagation formula for the average shear magnitude. We then investigate the evolution of anisotropic average vacuum models and those filled with pressureless matter. In the latter case we show that the backreaction effects can modify the familiar Kasner-like singularity and potentially remove Mixmaster-type oscillations. The presence of nonzero average shear in our equations also allows us to examine the constraints that a phase of backreaction-driven accelerated expansion might put on the anisotropy of the averaged domain. We close by assessing the status of these and other attempts to define and calculate 'average' spacetime behaviour in general relativity
Tsagas, C G
2001-01-01
The vector nature of magnetic fields and the general relativistic geometrical interpretation of gravity lead to a unique coupling between magnetism and spacetime curvature, by effectively transferring the field properties into the spacetime itself. The key magnetic property appears to be the tension of the field lines. Combined with geometry, the magnetic tension triggers a range of rather unexpected effects with profound implications. The field suppresses or boosts density fluctuations depending on the strength of the curvature deformation. It can act as an effective cosmological constant or mimic a time-decaying quintessence. Moreover, even weak magnetic fields become key players when the curvature is strong. For instance, a seed field could halt the accelerated phase in certain inflationary models. The magnetic tension also damps gravity waves and shows an intriguing tendency to smooth out spatial curvature distortions. We describe the nature and the range of these effects and discuss their potential impli...
Tidal features of classical Milky Way satellites in a $\\Lambda$CDM universe
Wang, M -Y; Cooper, Andrew P; Sawala, Till; Strigari, Louis E; Frenk, Carlos S; Navarro, Julio F; Oman, Kyle; Schaller, Matthieu
2016-01-01
We use the APOSTLE cosmological hydrodynamic simulations to examine the effects of tidal stripping on cold dark matter (CDM) sub haloes that host three of the most luminous Milky Way (MW) dwarf satellite galaxies: Fornax, Sculptor, and Leo I. We identify simulated satellites that match the observed spatial and kinematic distributions of stars in these galaxies, and track their evolution after infall. We find $\\sim$ 30$\\%$ of subhaloes hosting satellites with present-day stellar mass $10^6$-$10^8$ $M_{\\odot}$ experience $>20\\%$ stellar mass loss after infall. Fornax analogues have earlier infall times compared to Sculptor and Leo I analogues. Star formation in Fornax analogues continues for $\\sim3$-$6$ Gyr after infall, whereas Sculptor and Leo I analogues stop forming stars $< 2$-$3$ Gyr after infall. Fornax analogues typically show more significant stellar mass loss and exhibit stellar tidal tails, whereas Sculptor and Leo I analogues, which are more deeply embedded in their host DM haloes at infall, do n...
Galaxy morphology, kinematics and clustering in a hydrodynamic simulation of a LambdaCDM universe
Croft, Rupert A C; Springel, Volker; Hernquist, Lars
2008-01-01
We explore galaxy properties and their link with environment and clustering using a population of ~1000 galaxies formed in a high resolution hydrodynamic simulation of the Lambda CDM cosmology. At the redshift we concentrate on, z=1, the spatial resolution is 1.4 proper kpc/h and Milky-way sized disk galaxies contain ~10^5 particles within their virial radii. We include supermassive black hole accretion and feedback as well as a multiphase model for star formation. We find that a number of familiar qualitative relationships hold approximately between galaxy properties, for example, galaxies lie between two broad extremes of type, where ``late'' types tend to be smaller in size, have lower circular velocities, younger stars, higher star formation rates, larger disk to bulge ratios and lower Sersic indices than ``early types''. As in previous studies the stellar component of disk galaxies is not as rotationally supported as in observations. Bulges contain too much of the stellar mass, although disks do have sca...
The properties of "dark" {\\Lambda}CDM halos in the Local Group
Benítez-Llambay, Alejandro; Frenk, Carlos S; Sawala, Till; Oman, Kyle; Fattahi, Azadeh; Schaller, Matthieu; Schaye, Joop; Crain, Rob; Theuns, Tom
2016-01-01
We examine the baryon content of low-mass {\\Lambda}CDM halos $(10^8
Voids in cosmological simulations over cosmic time
Wojtak, Radosław; Abel, Tom
2016-01-01
We study evolution of voids in cosmological simulations using a new method for tracing voids over cosmic time. The method is based on tracking watershed basins (contiguous regions around density minima) of well developed voids at low redshift, on a regular grid of density field. It enables us to construct a robust and continuous mapping between voids at different redshifts, from initial conditions to the present time. We discuss how the new approach eliminates strong spurious effects of numerical origin when voids evolution is traced by matching voids between successive snapshots (by analogy to halo merger trees). We apply the new method to a cosmological simulation of a standard LambdaCDM cosmological model and study evolution of basic properties of typical voids (with effective radii between 6Mpc/h and 20Mpc/h at redshift z=0) such as volumes, shapes, matter density distributions and relative alignments. The final voids at low redshifts appear to retain a significant part of the configuration acquired in in...
The best-fit universe. [cosmological models
Turner, Michael S.
1991-01-01
Inflation provides very strong motivation for a flat Universe, Harrison-Zel'dovich (constant-curvature) perturbations, and cold dark matter. However, there are a number of cosmological observations that conflict with the predictions of the simplest such model: one with zero cosmological constant. They include the age of the Universe, dynamical determinations of Omega, galaxy-number counts, and the apparent abundance of large-scale structure in the Universe. While the discrepancies are not yet serious enough to rule out the simplest and most well motivated model, the current data point to a best-fit model with the following parameters: Omega(sub B) approximately equal to 0.03, Omega(sub CDM) approximately equal to 0.17, Omega(sub Lambda) approximately equal to 0.8, and H(sub 0) approximately equal to 70 km/(sec x Mpc) which improves significantly the concordance with observations. While there is no good reason to expect such a value for the cosmological constant, there is no physical principle that would rule out such.
Neutrino mass bounds from neutrinoless double beta-decays and cosmological probes
Indian Academy of Sciences (India)
Yong-Yeon Keum
2016-02-01
We investigate the way the total mass sum of neutrinos can be constrained from the neutrinoless double beta-decay and cosmological probes with cosmic microwave background (CMBR), large-scale structures including 2dFGRS and SDSS datasets. First we discuss, in brief, the current status of neutrino mass bounds from neutrino beta decays and cosmic constraint within the flat CMD model. In addition, we explore the interacting neutrino dark-energy model, where the evolution of neutrino masses is determined by quintessence scalar field, which is responsible for cosmic acceleration. Assuming the flatness of the Universe, the constraint we can derive from the current observation is < 0.87 eV at 95% confidence level, which is consistent with < 0.68 eV in the flat CDM model without Lyman alpha forest data. In the presence of Lyman- forest data, interacting dark-energy models prefer a weaker bound < 0.43 eV to < 0.17 eV (Seljark et al). Finally, we discuss the future prospect of the neutrino mass bound with weak-lensing effects.
Sehgal, Neelima; Trac, Hy; Acquaviva, Viviana; Ade, Peter A. R.; Aguirre, Paula; Amiri, Mandana; Appel, John W.; Barrientos, L. Felipe; Battistelli, Elia S.; Bond, J. Richard; Brown, Ben; Burger, Bryce; Chervenak, Jay; Das, Sudeep; Devlin, Mark J.; Dicker, Simon R.; Doriese, W. Bertrand; Dunkley, Joanna; Duenner, Rolando; Essinger-Hileman, Thomas; Fisher, Ryan P.; Fowler, Joseph W.; Hajian, Amir; Halpern, Mark; Wollack, Ed
2010-01-01
We present constraints on cosmological parameters based on a sample of Sunyaev-Zel'dovich-selected galaxy clusters detected in a millimeter-wave survey by the Atacama Cosmology Telescope. The cluster sample used in this analysis consists of 9 optically-confirmed high-mass clusters comprising the high-significance end of the total cluster sample identified in 455 square degrees of sky surveyed during 2008 at 148 GHz. We focus on the most massive systems to reduce the degeneracy between unknown cluster astrophysics and cosmology derived from SZ surveys. We describe the scaling relation between cluster mass and SZ signal with a 4-parameter fit. Marginalizing over the values of the parameters in this fit with conservative priors gives (sigma)8 = 0.851 +/- 0.115 and w = -1.14 +/- 0.35 for a spatially-flat wCDM cosmological model with WMAP 7-year priors on cosmological parameters. This gives a modest improvement in statistical uncertainty over WMAP 7-year constraints alone. Fixing the scaling relation between cluster mass and SZ signal to a fiducial relation obtained from numerical simulations and calibrated by X-ray observations, we find (sigma)8 + 0.821 +/- 0.044 and w = -1.05 +/- 0.20. These results are consistent with constraints from WMAP 7 plus baryon acoustic oscillations plus type Ia supernova which give (sigma)8 = 0.802 +/- 0.038 and w = -0.98 +/- 0.053. A stacking analysis of the clusters in this sample compared to clusters simulated assuming the fiducial model also shows good agreement. These results suggest that, given the sample of clusters used here, both the astrophysics of massive clusters and the cosmological parameters derived from them are broadly consistent with current models.
Cosmological evolution of the gravitational entropy of the large-scale structure
Marozzi, Giovanni; Uzan, Jean-Philippe; Umeh, Obinna; Clarkson, Chris
2015-10-01
We consider the entropy associated with the large-scale structure of the Universe in the linear regime, where the Universe can be described by a perturbed Friedmann-Lemaître spacetime. In particular, we compare two different definitions proposed in the literature for the entropy using a spatial averaging prescription. For one definition, the entropy of the large-scale structure for a given comoving volume always grows with time, both for a CDM and a CDM model. In particular, while it diverges for a CDM model, it saturates to a constant value in the presence of a cosmological constant. The use of a light-cone averaging prescription in the context of the evaluation of the entropy is also discussed.
Cosmological evolution of the gravitational entropy of the large-scale structure
Marozzi, Giovanni; Umeh, Obinna; Clarkson, Chris
2015-01-01
This article derives the entropy associated with the large-scale structure of the Universe in the linear regime, where the Universe can be described by a perturbed Friedmann-Lema\\^{\\i}tre spacetime. In particular, it compares two different definitions proposed in the literature for the entropy using a spatial averaging prescription. For one definition, the entropy of the large-scale structure and for a given comoving volume always grows with time, both for a CDM and a $\\Lambda$CDM model. In particular, while it diverges for a CDM model, it saturates to a constant value in the presence of a cosmological constant. The use of a light-cone averaging prescription in the context of the evaluation of the entropy is also discussed.
New Cosmological Model and Its Implications on Observational Data Interpretation
Directory of Open Access Journals (Sweden)
Vlahovic Branislav
2013-09-01
Full Text Available The paradigm of ΛCDM cosmology works impressively well and with the concept of inflation it explains the universe after the time of decoupling. However there are still a few concerns; after much effort there is no detection of dark matter and there are significant problems in the theoretical description of dark energy. We will consider a variant of the cosmological spherical shell model, within FRW formalism and will compare it with the standard ΛCDM model. We will show that our new topological model satisfies cosmological principles and is consistent with all observable data, but that it may require new interpretation for some data. Considered will be constraints imposed on the model, as for instance the range for the size and allowed thickness of the shell, by the supernovae luminosity distance and CMB data. In this model propagation of the light is confined along the shell, which has as a consequence that observed CMB originated from one point or a limited space region. It allows to interpret the uniformity of the CMB without inflation scenario. In addition this removes any constraints on the uniformity of the universe at the early stage and opens a possibility that the universe was not uniform and that creation of galaxies and large structures is due to the inhomogeneities that originated in the Big Bang.
Semi-analytic galaxy formation in coupled dark energy cosmologies
Fontanot, Fabio; Bianchi, Davide
2015-01-01
Among the possible alternatives to the standard cosmological model ($\\Lambda$CDM), coupled Dark Energy models postulate that Dark Energy (DE), seen as a dynamical scalar field, may interact with Dark Matter (DM), giving rise to a "fifth-force", felt by DM particles only. In this paper, we study the impact of these cosmologies on the statistical properties of galaxy populations by combining high-resolution numerical simulations with semi-analytic models (SAM) of galaxy formation and evolution. New features have been implemented in the reference SAM in order to have it run self-consistently and calibrated on these cosmological simulations. They include an appropriate modification of the mass temperature relation and of the baryon fraction in DM haloes, due to the different virial scalings and to the gravitational bias, respectively. Our results show that the predictions of our coupled-DE SAM do not differ significantly from theoretical predictions obtained with standard SAMs applied to a reference $\\Lambda$CDM ...
Simple inhomogeneous cosmological (toy) models
Chirinos Isidro, Eddy G.; Zuñiga Vargas, Cristofher; Zimdahl, Winfried
2016-05-01
Based on the Lemaître-Tolman-Bondi (LTB) metric we consider two flat inhomogeneous big-bang models. We aim at clarifying, as far as possible analytically, basic features of the dynamics of the simplest inhomogeneous models and to point out the potential usefulness of exact inhomogeneous solutions as generalizations of the homogeneous configurations of the cosmological standard model. We discuss explicitly partial successes but also potential pitfalls of these simplest models. Although primarily seen as toy models, the relevant free parameters are fixed by best-fit values using the Joint Light-curve Analysis (JLA)-sample data. On the basis of a likelihood analysis we find that a local hump with an extension of almost 2 Gpc provides a better description of the observations than a local void for which we obtain a best-fit scale of about 30 Mpc. Future redshift-drift measurements are discussed as a promising tool to discriminate between inhomogeneous configurations and the ΛCDM model.
THE KINEMATICS OF THE LOCAL GROUP IN A COSMOLOGICAL CONTEXT
International Nuclear Information System (INIS)
Recent observations constrained the tangential velocity of M31 with respect to the Milky Way to be vM31,tan –1and the radial velocity to be in the range vM31,rad = –109 ± 4.4 km s–1. In this study we use a large volume high-resolution N-body cosmological simulation (Bolshoi) together with three constrained simulations to statistically study this kinematics in the context of the Λ cold dark matter (ΛCDM). The comparison of the ensembles of simulated pairs with the observed Local Group (LG) at the 1σ level in the uncertainties has been done with respect to the radial and tangential velocities, the reduced orbital energy (etot), angular momentum (lorb), and the dimensionless spin parameter, λ. Our main results are (1) the preferred radial and tangential velocities for pairs in ΛCDM are vr = –80 ± 20 km s–1 and vt = 50 ± 10 km s–1, (2) pairs around that region are 3-13 times more common than pairs within the observational values, (3) 15%-24% of LG-like pairs in ΛCDM have energy and angular momentum consistent with observations, while (4) 9%-13% of pairs in the same sample show similar values in the inferred dimensionless spin parameter. It follows that within current observational uncertainties the quasi-conserved quantities that characterize the orbit of the LG, i.e., etot, lorb, and λ, do not challenge the standard ΛCDM model, but the model is in tension with regard to the actual values of the radial and tangential velocities. This might hint to a problem of the ΛCDM model to reproduce the observed LG.
THE KINEMATICS OF THE LOCAL GROUP IN A COSMOLOGICAL CONTEXT
Energy Technology Data Exchange (ETDEWEB)
Forero-Romero, J. E. [Departamento de Fisica, Universidad de los Andes, Cra. 1 No. 18A-10, Edificio Ip, Bogota (Colombia); Hoffman, Y. [Racah Institute of Physics, The Hebrew University of Jerusalem, 91904 Jerusalem (Israel); Bustamante, S. [Instituto de Fisica-FCEN, Universidad de Antioquia, Calle 67 No. 53-108, Medellin (Colombia); Gottloeber, S. [Leibniz-Institut fuer Astrophysik, Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany); Yepes, G., E-mail: je.forero@uniandes.edu.co [Grupo de Astrofisica, Departamento de Fisica Teorica, Universidad Autonoma de Madrid, Cantoblanco E-280049 (Spain)
2013-04-10
Recent observations constrained the tangential velocity of M31 with respect to the Milky Way to be v{sub M31,tan} < 34.4 km s{sup -1}and the radial velocity to be in the range v{sub M31,rad} = -109 {+-} 4.4 km s{sup -1}. In this study we use a large volume high-resolution N-body cosmological simulation (Bolshoi) together with three constrained simulations to statistically study this kinematics in the context of the {Lambda} cold dark matter ({Lambda}CDM). The comparison of the ensembles of simulated pairs with the observed Local Group (LG) at the 1{sigma} level in the uncertainties has been done with respect to the radial and tangential velocities, the reduced orbital energy (e{sub tot}), angular momentum (l{sub orb}), and the dimensionless spin parameter, {lambda}. Our main results are (1) the preferred radial and tangential velocities for pairs in {Lambda}CDM are v{sub r} = -80 {+-} 20 km s{sup -1} and v{sub t} = 50 {+-} 10 km s{sup -1}, (2) pairs around that region are 3-13 times more common than pairs within the observational values, (3) 15%-24% of LG-like pairs in {Lambda}CDM have energy and angular momentum consistent with observations, while (4) 9%-13% of pairs in the same sample show similar values in the inferred dimensionless spin parameter. It follows that within current observational uncertainties the quasi-conserved quantities that characterize the orbit of the LG, i.e., e{sub tot}, l{sub orb}, and {lambda}, do not challenge the standard {Lambda}CDM model, but the model is in tension with regard to the actual values of the radial and tangential velocities. This might hint to a problem of the {Lambda}CDM model to reproduce the observed LG.
Braneworld cosmology and noncommutative inflation
Calcagni, Gianluca
2005-03-01
In this work we develop the patch formalism, an approach providing a very simple and compact description of braneworld-motivated cosmologies with nonstandard effective Friedmann equations. In particular, the Hubble parameter is assumed to depend on some power of the brane energy density, H^2 propto rho^q. The high-energy limit of Randall-Sundrum (q=2) and Gauss-Bonnet (q=2/3) braneworlds are considered, during an accelerating era triggered by a single ordinary or tachyonic scalar field. The inflationary dynamics, solutions, and spectra are provided. Using the latest results from WMAP and other experiments for estimates of cosmological observables, it is shown that future data and missions can in principle discriminate between standard four-dimensional and braneworld scenarios. The issue of non-Gaussianity is also studied within nonlinear perturbation theory. The introduction of a fundamental energy scale reinforces these results. Several classes of noncommutative inflationary models are considered and their features analyzed in a number of ways and energy regimes. Finally, we establish dual relations between inflationary, cyclic/ekpyrotic and phantom cosmologies, as well as between scalar-driven and tachyon-driven cosmologies. The exact dualities relating the four-dimensional spectra are broken in favour of their braneworld counterparts. The dual solutions display new interesting features because of the modification of the effective Friedmann equation on the brane.
Extracting the resource rent from the CDM projects. Can the Chinese Government do better?
Energy Technology Data Exchange (ETDEWEB)
Liu, Xuemei [Department of Economics, California State University, 1250 Bellflower Blvd., Long Beach, CA 90840 (United States)
2010-02-15
The revenue generated from a CDM project in China will be shared by the government and the project owner, and is also subject to the corporate income tax. This paper studies the impacts of the revenue sharing policy and income tax on the CDM market. The economic model presented in this paper shows that higher-cost CDM projects will be more affected by the CDM policies than lower-cost projects. In addition, the majority of CERs will be generated from lower-cost projects. This kind of distribution of CERs across different types of CDM projects, which is in line with the current picture of the CDM market in China, is not consistent with the goal of sustainable development. A simulation shows that a type-by-type tax/fee scheme would be more effective in assisting sustainable development than the current CDM policies. The study also suggests the government use negative tax/fee with the type-by-type scheme to subsidize the CDM projects that generate large sustainability benefits but would otherwise not be developed due to high costs. If all of the revenue from the CDM is recycled, it is estimated that CERs generation will increase by 98.28 MtC, mainly from the CDM projects that have substantial sustainability benefits for the host country. (author)
Extracting the resource rent from the CDM projects: Can the Chinese Government do better?
Energy Technology Data Exchange (ETDEWEB)
Liu Xuemei, E-mail: xliu2@csulb.ed [Department of Economics, California State University, 1250 Bellflower Blvd., Long Beach, CA 90840 (United States)
2010-02-15
The revenue generated from a CDM project in China will be shared by the government and the project owner, and is also subject to the corporate income tax. This paper studies the impacts of the revenue sharing policy and income tax on the CDM market. The economic model presented in this paper shows that higher-cost CDM projects will be more affected by the CDM policies than lower-cost projects. In addition, the majority of CERs will be generated from lower-cost projects. This kind of distribution of CERs across different types of CDM projects, which is in line with the current picture of the CDM market in China, is not consistent with the goal of sustainable development. A simulation shows that a type-by-type tax/fee scheme would be more effective in assisting sustainable development than the current CDM policies. The study also suggests the government use negative tax/fee with the type-by-type scheme to subsidize the CDM projects that generate large sustainability benefits but would otherwise not be developed due to high costs. If all of the revenue from the CDM is recycled, it is estimated that CERs generation will increase by 98.28 MtC, mainly from the CDM projects that have substantial sustainability benefits for the host country.
Extracting the resource rent from the CDM projects: Can the Chinese Government do better?
International Nuclear Information System (INIS)
The revenue generated from a CDM project in China will be shared by the government and the project owner, and is also subject to the corporate income tax. This paper studies the impacts of the revenue sharing policy and income tax on the CDM market. The economic model presented in this paper shows that higher-cost CDM projects will be more affected by the CDM policies than lower-cost projects. In addition, the majority of CERs will be generated from lower-cost projects. This kind of distribution of CERs across different types of CDM projects, which is in line with the current picture of the CDM market in China, is not consistent with the goal of sustainable development. A simulation shows that a type-by-type tax/fee scheme would be more effective in assisting sustainable development than the current CDM policies. The study also suggests the government use negative tax/fee with the type-by-type scheme to subsidize the CDM projects that generate large sustainability benefits but would otherwise not be developed due to high costs. If all of the revenue from the CDM is recycled, it is estimated that CERs generation will increase by 98.28 MtC, mainly from the CDM projects that have substantial sustainability benefits for the host country.
Extracting the resource rent from the CDM projects. Can the Chinese Government do better?
International Nuclear Information System (INIS)
The revenue generated from a CDM project in China will be shared by the government and the project owner, and is also subject to the corporate income tax. This paper studies the impacts of the revenue sharing policy and income tax on the CDM market. The economic model presented in this paper shows that higher-cost CDM projects will be more affected by the CDM policies than lower-cost projects. In addition, the majority of CERs will be generated from lower-cost projects. This kind of distribution of CERs across different types of CDM projects, which is in line with the current picture of the CDM market in China, is not consistent with the goal of sustainable development. A simulation shows that a type-by-type tax/fee scheme would be more effective in assisting sustainable development than the current CDM policies. The study also suggests the government use negative tax/fee with the type-by-type scheme to subsidize the CDM projects that generate large sustainability benefits but would otherwise not be developed due to high costs. If all of the revenue from the CDM is recycled, it is estimated that CERs generation will increase by 98.28 MtC, mainly from the CDM projects that have substantial sustainability benefits for the host country. (author)
Cosmology and particle physics
International Nuclear Information System (INIS)
The author reviews the standard cosmology, focusing on primordial nucleosynthesis, and discusses how the standard cosmology has been used to place constraints on the properties of various particles. Baryogenesis is examined in which the B, C, CP violating interactions in GUTs provide a dynamical explanation for the predominance of matter over antimatter and the present baryon-to-baryon ratio. Monoposes, cosmology and astrophysics are reviewed. The author also discusses supersymmetry/supergravity and cosmology, superstrings and cosmology in extra dimensions, and axions, astrophics, and cosmology
PSCz Superclusters Detection, Shapes & Cosmological Implications
Basilakos, S; Rowan-Robinson, M
2000-01-01
We study the possibility of correctly identifying superclusters, from the smooth galaxy density field of the PSCz redshift catalogue, and of recovering their true shapes in the presence of a bias introduced by the coupling between the selection function and the constant radius smoothing. Using simulations we quantify such systematic biases in the smoothed PSCz density field and after applying the necessary corrections we study the PSCz supercluster multiplicity and morphologies using a differential geometry definition of shape. Our results strongly suggest that filamentariness is the dominant morphological feature of PSCz superclusters. Finally, we compare our results with those expected in three different cosmological models and find that the LCDM model performs better than Omega_m=1 CDM models.
Undermining the Cosmological Principle Observational Characteristics of Inhomogeneous Cosmologies
Barrett, R K
2000-01-01
We challenge the widely held belief that the cosmological principle is an obvious consequence of the observed isotropy of the cosmic microwave background radiation (CMBR), combined with the Copernican principle. We perform a detailed study of a class of inhomogeneous perfect fluid cosmological models admitting an isotropic radiation field with a view to assessing their viability as models of the real universe. These spacetimes are distinguished from FLRW universes by the presence of inhomogeneous pressure, which results in an acceleration of the fluid (fundamental observers). We examine their physical, geometrical and observational characteristics \\emph{for all observer positions} in the spacetimes. To this end, we derive \\emph{exact, analytic} expressions for the distance-redshift relations and anisotropies for all observer locations, and compare their predictions with available observational constraints. The isotropy constraints derived from `local' observations (redshift $\\lesssim 1$) are also considered, ...
How Fabulous Is Fab 5 Cosmology?
Linder, Eric V
2013-01-01
Extended gravity origins for cosmic acceleration can solve some fine tuning issues and have useful characteristics, but generally have little to say regarding the cosmological constant problem. Fab 5 gravity can be ghost free and stable, have attractor solutions in the past and future, and possess self tuning that solves the original cosmological constant problem. Here we show however it does not possess all these qualities at the same time. We also demonstrate that the self tuning is so powerful that it not only cancels the cosmological constant but also all other energy density, and we derive the scalings of its approach to a renormalized de Sitter cosmology. While this strong cancellation is bad for the late universe, it greatly eases early universe inflation.
Bayesian comparison of non-standard cosmologies using type Ia supernovae and BAO data
Santos, B; Alcaniz, J S
2016-01-01
We use the most recent type Ia supernovae (SNe Ia) observations to perform a statistical comparison between the standard $\\Lambda$CDM model and its extensions ($w$CDM and $w(z)$CDM) and some alternative cosmologies, namely: the Dvali--Gabadadze--Porrati (DGP) model, a power-law $f(R)$ scenario in the metric formalism and an example of vacuum decay ($\\Lambda(t)$CDM) cosmology in which the dilution of pressureless matter is attenuated with respect to the usual $a^{-3}$ scaling due to the interaction of the dark matter and dark energy fields. We perform a Bayesian model selection analysis using the Affine-Invariant Ensemble Sampler Monte-Carlo method. In order to obtain the posterior distribution for the parameters of each model, we use the Joint Lightcurve Analysis (JLA) SNe Ia compilation containing 740 events in the interval $0.01 < z < 1.3$. The data are analysed with the SALT-II light-curve fitter and the model selection is then performed by computing the Bayesian evidence of each model and the Bayes ...
Dynamical system approach to scalar-vector-tensor cosmology
Ghaffarnejad, H
2016-01-01
We use scalar-vector-tensor gravity [1] which is obtained by generalizing Brans Dicke (BD) gravity model [2] via dynamical vector field. We study flat Friedmann Robertson Walker (FRW) cosmology by using dynamical system approach in the presence of self interaction BD potential and perfect fluid matter stress tensor. We obtained 3 critical points for $\\Lambda CDM$ vacuum de Sitter era which one of them is spiral attractor absolutely independent of particular values of the BD parameter $\\omega$ but not two other critical points. The latter take real values only for $-0.54-0.54.$ Even if the eigne values become complex imaginary where $\\omega\
Constraining interacting dark energy models with latest cosmological observations
Xia, Dong-Mei; Wang, Sai
2016-08-01
The local measurement of H0 is in tension with the prediction of ΛCDM model based on the Planck data. This tension may imply that dark energy is strengthened in the late-time Universe. We employ the latest cosmological observations on CMB, BAO, LSS, SNe, H(z) and H0 to constrain several interacting dark energy models. Our results show no significant indications for the interaction between dark energy and dark matter. The H0 tension can be moderately alleviated, but not totally released.
Constraining interacting dark energy models with latest cosmological observations
Xia, Dong-Mei
2016-01-01
The local measurement of $H_0$ is in tension with the prediction of $\\Lambda$CDM model based on the Planck data. This tension may imply that dark energy is strengthened in the late-time Universe. We employ the latest cosmological observations on CMB, BAO, LSS, SNe, $H(z)$ and $H_0$ to constrain several interacting dark energy models. Our results show no significant indications for the interaction between dark energy and dark matter. The $H_0$ tension can be moderately alleviated, but not totally released.
A comparison of cosmological models using strong gravitational lensing galaxies
International Nuclear Information System (INIS)
Strongly gravitationally lensed quasar-galaxy systems allow us to compare competing cosmologies as long as one can be reasonably sure of the mass distribution within the intervening lens. In this paper, we assemble a catalog of 69 such systems from the Sloan Lens ACS and Lens Structure and Dynamics surveys suitable for this analysis, and carry out a one-on-one comparison between the standard model, ΛCDM, and the Rh=ct universe, which has thus far been favored by the application of model selection tools to other kinds of data. We find that both models account for the lens observations quite well, though the precision of these measurements does not appear to be good enough to favor one model over the other. Part of the reason is the so-called bulge-halo conspiracy that, on average, results in a baryonic velocity dispersion within a fraction of the optical effective radius virtually identical to that expected for the whole luminous-dark matter distribution modeled as a singular isothermal ellipsoid, though with some scatter among individual sources. Future work can greatly improve the precision of these measurements by focusing on lensing systems with galaxies as close as possible to the background sources. Given the limitations of doing precision cosmological testing using the current sample, we also carry out Monte Carlo simulations based on the current lens measurements to estimate how large the source catalog would have to be in order to rule out either model at a ∼99.7% confidence level. We find that if the real cosmology is ΛCDM, a sample of ∼200 strong gravitational lenses would be sufficient to rule out Rh=ct at this level of accuracy, while ∼300 strong gravitational lenses would be required to rule out ΛCDM if the real universe were instead Rh=ct. The difference in required sample size reflects the greater number of free parameters available to fit the data with ΛCDM. We point out that, should the Rh=ct universe eventually emerge as the correct
Constraining interacting dark energy models with latest cosmological observations
Xia, Dong-Mei; Wang, Sai
2016-01-01
The local measurement of $H_0$ is in tension with the prediction of $\\Lambda$CDM model based on the Planck data. This tension may imply that dark energy is strengthened in the late-time Universe. We employ the latest cosmological observations on CMB, BAO, LSS, SNe, $H(z)$ and $H_0$ to constrain several interacting dark energy models. Our results show no significant indications for the interaction between dark energy and dark matter. The $H_0$ tension can be moderately alleviated, but not tota...
A comparison of cosmological models using strong gravitational lensing galaxies
Energy Technology Data Exchange (ETDEWEB)
Melia, Fulvio; Wei, Jun-Jie; Wu, Xue-Feng, E-mail: fmelia@email.arizona.edu, E-mail: jjwei@pmo.ac.cn, E-mail: xfwu@pmo.ac.cn, E-mail: fmelia@email.arizona.edu, E-mail: jjwei@pmo.ac.cn, E-mail: xfwu@pmo.ac.cn [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)
2015-01-01
Strongly gravitationally lensed quasar-galaxy systems allow us to compare competing cosmologies as long as one can be reasonably sure of the mass distribution within the intervening lens. In this paper, we assemble a catalog of 69 such systems from the Sloan Lens ACS and Lens Structure and Dynamics surveys suitable for this analysis, and carry out a one-on-one comparison between the standard model, ΛCDM, and the R{sub h}=ct universe, which has thus far been favored by the application of model selection tools to other kinds of data. We find that both models account for the lens observations quite well, though the precision of these measurements does not appear to be good enough to favor one model over the other. Part of the reason is the so-called bulge-halo conspiracy that, on average, results in a baryonic velocity dispersion within a fraction of the optical effective radius virtually identical to that expected for the whole luminous-dark matter distribution modeled as a singular isothermal ellipsoid, though with some scatter among individual sources. Future work can greatly improve the precision of these measurements by focusing on lensing systems with galaxies as close as possible to the background sources. Given the limitations of doing precision cosmological testing using the current sample, we also carry out Monte Carlo simulations based on the current lens measurements to estimate how large the source catalog would have to be in order to rule out either model at a ∼99.7% confidence level. We find that if the real cosmology is ΛCDM, a sample of ∼200 strong gravitational lenses would be sufficient to rule out R{sub h}=ct at this level of accuracy, while ∼300 strong gravitational lenses would be required to rule out ΛCDM if the real universe were instead R{sub h}=ct. The difference in required sample size reflects the greater number of free parameters available to fit the data with ΛCDM. We point out that, should the R{sub h}=ct universe eventually
Dvali-Gabadadze-Porrati Cosmology in Bianchi I brane
Ansari, Rizwan Ul Haq
2008-01-01
The dynamics of Dvali-Gabadadze-Porrati Cosmology (DGP) braneworld with an anisotropic brane is studied. The Friedmann equations and their solutions are obtained for two branches of anisotropic DGP model. The late time behavior in DGP cosmology is examined in the presence of anisotropy which shows that universe enters a self-accelerating phase much later compared to the isotropic case. The acceleration conditions and slow-roll conditions for inflation are obtained.
Observational constraints on dark energy cosmological model parameters
Farooq, Muhammad Omer
2013-01-01
The expansion rate of the Universe changes with time, initially slowing (decelerating) when the universe was matter dominated, because of the mutual gravitational attraction of all the matter in it, and more recently speeding up (accelerating). A number of cosmological observations now strongly support the idea that the Universe is spatially flat (provided the dark energy density is at least approximately time independent) and is currently undergoing an accelerated cosmological expansion. A m...
Nojiri, S; Oikonomou, V K
2016-01-01
We combine the unimodular gravity and mimetic gravity theories into a unified theoretical framework, which is proposed to solve the cosmological constant problem and the dark matter issue. After providing the formulation of the unimodular mimetic gravity and investigating all the new features that the vacuum unimodular gravity implies, by using the underlying reconstruction method, we realize some well known cosmological evolutions, with some of these being exotic for the ordinary Einstein-Hilbert gravity. Specifically we provide the vacuum unimodular mimetic gravity description of the de Sitter cosmology, of the perfect fluid with constant equation of state cosmology, of the Type IV singular cosmology and of the $R^2$ inflation cosmology. Moreover, we investigate how cosmologically viable cosmologies, which are compatible with the recent observational data, can be realized by the vacuum unimodular mimetic gravity. Since in some cases, the graceful exit from inflation problem might exist, we provide a qualita...
Braneworld cosmology and noncommutative inflation
Calcagni, G
2005-01-01
In this work we develop the patch formalism, an approach providing a very simple and compact description of braneworld-motivated cosmologies with nonstandard effective Friedmann equations. In particular, the Hubble parameter is assumed to depend on some power of the brane energy density, H^2 \\propto \\rho^q. The high-energy limit of Randall-Sundrum (q=2) and Gauss-Bonnet (q=2/3) braneworlds are considered, during an accelerating era triggered by a single ordinary or tachyonic scalar field. The inflationary dynamics, solutions, and spectra are provided. Using the latest results from WMAP and other experiments for estimates of cosmological observables, it is shown that future data and missions can in principle discriminate between standard four-dimensional and braneworld scenarios. The issue of non-Gaussianity is also studied within nonlinear perturbation theory. The introduction of a fundamental energy scale reinforces these results. Several classes of noncommutative inflationary models are considered and their...
A COMPARATIVE ANALYSIS OF THE SUPERNOVA LEGACY SURVEY SAMPLE WITH ΛCDM AND THE R{sub h}=ct UNIVERSE
Energy Technology Data Exchange (ETDEWEB)
Wei, Jun-Jie; Wu, Xue-Feng; Melia, Fulvio [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China); Maier, Robert S., E-mail: jjwei@pmo.ac.cn, E-mail: xfwu@pmo.ac.cn, E-mail: fmelia@email.arizona.edu, E-mail: rsm@math.arizona.edu [Department of Mathematics, The Statistics Program, and Department of Physics, The University of Arizona, AZ 85721 (United States)
2015-03-15
The use of Type Ia supernovae (SNe Ia) has thus far produced the most reliable measurement of the expansion history of the universe, suggesting that ΛCDM offers the best explanation for the redshift–luminosity distribution observed in these events. However, analysis of other kinds of sources, such as cosmic chronometers, gamma-ray bursts, and high-z quasars, conflicts with this conclusion, indicating instead that the constant expansion rate implied by the R{sub h} = ct universe is a better fit to the data. The central difficulty with the use of SNe Ia as standard candles is that one must optimize three or four nuisance parameters characterizing supernova (SN) luminosities simultaneously with the parameters of an expansion model. Hence, in comparing competing models, one must reduce the data independently for each. We carry out such a comparison of ΛCDM and the R{sub h} = ct universe using the SN Legacy Survey sample of 252 SN events, and show that each model fits its individually reduced data very well. However, since R{sub h} = ct has only one free parameter (the Hubble constant), it follows from a standard model selection technique that it is to be preferred over ΛCDM, the minimalist version of which has three (the Hubble constant, the scaled matter density, and either the spatial curvature constant or the dark energy equation-of-state parameter). We estimate using the Bayes Information Criterion that in a pairwise comparison, the likelihood of R{sub h} = ct is ∼90%, compared with only ∼10% for a minimalist form of ΛCDM, in which dark energy is simply a cosmological constant. Compared to R{sub h} = ct, versions of the standard model with more elaborate parametrizations of dark energy are judged to be even less likely.
Linking renewable energy CDM projects and TGC schemes: An analysis of different options
Energy Technology Data Exchange (ETDEWEB)
Del Rio, Pablo [Department of Economics and Business, Facultad de Ciencias Juridicas y Sociales, Universidad de Castilla-La Mancha, C/ Cobertizo de S. Pedro Martir s/n., Toledo-45071 (Spain)]. E-mail: pablo.rio@uclm.es
2006-11-15
Renewable energy CDM (RE-CDM) projects encourage cost-effective GHG mitigation and enhanced sustainable development opportunities for the host countries. CERs from CDM projects include the value of the former benefits (i.e., 'climate change benefits'), whereas the second can be given value through the issuing and trading of tradable green certificates (TGCs). Countries could agree to trade these TGCs, leading to additional revenues for the investors in renewable energy projects and, therefore, further encouraging the deployment of CDM projects, currently facing significant barriers. However, the design of a combination of CDM projects and TGC schemes raises several conflicting issues and leads to trade-offs. This paper analyses these issues, identifies the alternatives that may exist to link TGC schemes with RE-CDM projects and analyses the impacts of those options on different variables and actors.
Clean development Mechanism (CDM) Policy and Implementation in China
Zeng, Lei
2006-01-01
China is the second largest emitter of greenhouse gases (GHG) in the world. Since 68% of its primary energy is from coal, China’s average energy intensity is 7.5 times higher than the EU and 4.3 times higher than the US (EU, 2003). Therefore, introducing advanced clean technologies and management to China represents opportunities for Annex I countries to obtain low-cost CERs through CDM projects, and access to one of the largest energy conservation markets in the world. The Chinese government...
Stornaiolo, Cosimo
2001-01-01
In this paper we propose a model for the formation of the cosmological voids. We show that cosmological voids can form directly after the collapse of extremely large wavelength perturbations into low-density black holes or cosmological black holes (CBH). Consequently the voids are formed by the comoving expansion of the matter that surrounds the collapsed perturbation. It follows that the universe evolves, in first approximation, according to the Einstein-Straus cosmological model. We discuss...
Roos, Matts
2015-01-01
The Fourth Edition of Introduction to Cosmology provides a concise, authoritative study of cosmology at an introductory level. Starting from elementary principles and the early history of cosmology, the text carefully guides the student on to curved spacetimes, special and general relativity, gravitational lensing, the thermal history of the Universe, and cosmological models, including extended gravity models, black holes and Hawking's recent conjectures on the not-so-black holes.
Particle physics and cosmology
International Nuclear Information System (INIS)
During the past year, the research of the members of our group has spanned virtually all the topics at the interface of cosmology and particle physics: inflationary Universe scenarios, astrophysical and cosmological constraints on particle properties, ultra-high energy cosmic ray physics, quantum field theory in curved space-time, cosmology with extra dimensions, superstring cosmology, neutrino astronomy with large, underground detectors, and the formation of structure in the Universe
Constraints on Non-flat Cosmologies with Massive Neutrinos after Planck 2015
Chen, Yun; Ratra, Bharat; Biesiada, Marek; Li, Song; Zhu, Zong-Hong
2016-10-01
We investigate two dark energy cosmological models (i.e., the ΛCDM and ϕCDM models) with massive neutrinos assuming two different neutrino mass hierarchies in both the spatially flat and non-flat scenarios, where in the ϕCDM model the scalar field possesses an inverse power-law potential, V(ϕ) ∝ ϕ -α (α > 0). Cosmic microwave background data from Planck 2015, baryon acoustic oscillation data from 6dFGS, SDSS-MGS, BOSS-LOWZ and BOSS CMASS-DR11, the joint light-curve analysis compilation of SNe Ia apparent magnitude observations, and the Hubble Space Telescope H 0 prior, are jointly employed to constrain the model parameters. We first determine constraints assuming three species of degenerate massive neutrinos. In the spatially flat (non-flat) ΛCDM model, the sum of neutrino masses is bounded as Σm ν level (CL). Correspondingly, in the flat (non-flat) ϕCDM model, we find Σm ν < 0.164(0.301) eV at 95% CL. The inclusion of spatial curvature as a free parameter results in a significant broadening of confidence regions for Σm ν and other parameters. In the scenario where the total neutrino mass is dominated by the heaviest neutrino mass eigenstate, we obtain similar conclusions to those obtained in the degenerate neutrino mass scenario. In addition, the results show that the bounds on Σm ν based on two different neutrino mass hierarchies have insignificant differences in the spatially flat case for both the ΛCDM and ϕCDM models; however, the corresponding differences are larger in the non-flat case.
Thermodynamics properties of tachyon cosmology with non-minimal coupling to matter
Farajollahi, H.; Ravanpak, A.; Abolghasemi, M.
2016-01-01
Recently, we have investigated the dynamics of the universe in tachyon cosmology with non-minimal coupling to matter \\cite{faraj}-\\cite{faraj3}. In particular, for the interacting holographic dark energy (IHDE), the model is studied in \\cite{Ravanpak}. In the current work, a significant observational program has been conducted to unveil the model's thermodynamic properties. Our result shows that the IHDE version of our model better fits the observational data than $\\Lambda$CDM model. The firs...
The spatial distribution of galactic satellites in the Λ cold dark matter cosmology.
Wang, J.; Frenk, C.S.; Cooper, A. P.
2013-01-01
We investigate the spatial distribution of galactic satellites in high-resolution simulations of structure formation in the Λ cold dark matter (ΛCDM) model: the Aquarius dark matter simulations of individual haloes and the Millennium-II simulation of a large cosmological volume. To relate the simulations to observations of the Milky Way we use two alternative models to populate dark haloes with ‘visible’ galaxies: a semi-analytic model of galaxy formation and an abundance matching technique. ...
Cosmological evolution of thermal relic particles in $f(R)$ gravity
Capozziello, S; Lambiase, G; Pizza, L
2015-01-01
By considering $f(R)$ gravity models, the cosmic evolution is modified with respect to the standard $\\Lambda$CDM scenario. In particular, the thermal history of particles results modified. In this paper, we derive the evolution of relics particles (WIMPs) assuming a reliable $f(R)$ cosmological solution and taking into account observational constraints. The connection to the PAMELA experiment is also discussed. Results are consistent with constraints coming from BICEP2 and PLANCK experiments.
Indian Academy of Sciences (India)
Tarun Sandeep
2004-10-01
Cosmology is passing through a golden phase of rapid advance. The cosmology workshop at ICGC-2004 attracted a large number of research contributions to diverse topics of cosmology. I attempt to classify and summarize the research work and results of the oral and poster presentations made at the meeting.
Large Scale Impact of the Cosmological Population of Expanding Radio Galaxies
Barai, Paramita
2008-01-01
We seek to compute the fraction of the volume of the Universe filled by expanding cocoons of the cosmological population of radio galaxies over the Hubble time as well as the magnetic field infused by them, in order to assess their importance in the cosmic evolution of the Universe. Using N-body $\\Lambda$CDM simulations, radio galaxies distributed according to the observed radio luminosity function are allowed to evolve in a cosmological volume as using well defined prescriptions for their expansion. We find that the radio galaxies permeate $10 - 30%$ of the total volume with $\\sim 10^{-8}$ G magnetic field by the present epoch.
Cosmological parameter estimation from weak lensing. The case of $\\Omega_m$, $\\sigma_8$
Castañeda, Leonardo
2014-01-01
Propagation of light in the universe with structure which amplify and modify the shape of distant galaxies, producing a correlation between nearby and distant density of galaxies, is a phenomena very important in cosmology for determining cosmological parameters as the {\\Lambda}CDM. In this paper, we discuss the estimation of the two point correlation function in the gravitational shear produced by the large scale structure. We will compare the result given by gravitational lensing with the use of another alternatives such as a counting galaxy clusters. We also describe some software used in the gravitational lensing study for determining mass distribution models and images formation.
Carbon market risks and rewards: Firm perceptions of CDM investment decisions in Brazil and India
International Nuclear Information System (INIS)
The carbon market experiences of Brazil and India represent policy success stories under several criteria. A careful evaluation, however, reveals challenges to market development that should be addressed in order to make the rollout of a post-2012 CDM more effective. We conducted firm-level interviews covering 82 CDM plants in the sugar and cement sectors in Brazil and India, focusing on how individual managers understood the potential benefits and risks of undertaking clean development mechanism (CDM) investments. Our results indicate that the CDM operates in a far more complex way in practice than that of simply adding a marginal increment to a project's internal rate of return. Our results indicate the following: first, although anticipated revenue played a central role in most managers' decisions to pursue CDM investments, there was no standard practice to account for financial benefits of CDM investments; second, some managers identified non-financial reputational factors as their primary motivation for pursuing CDM projects; and third, under fluctuating regulatory regimes with real immediate costs and uncertain CDM revenue, managers favored projects that often did not require carbon revenue to be viable. The post-2012 CDM architecture can benefit from incorporating these insights, and in particular reassess goals for strict additionality and mechanisms for achieving it.
Integrated approach to cosmology: Combining CMB, large-scale structure and weak lensing
Nicola, Andrina; Amara, Adam
2016-01-01
Recent observational progress has led to the establishment of the standard $\\Lambda$CDM model for cosmology. This development is based on different cosmological probes that are usually combined through their likelihoods at the latest stage in the analysis. We implement here an integrated scheme for cosmological probes, which are combined in a common framework starting at the map level. This treatment is necessary as the probes are generally derived from overlapping maps and are thus not independent. It also allows for a thorough test of the cosmological model and of systematics through the consistency of different physical tracers. As a first application, we combine current measurements of the Cosmic Microwave Background (CMB) from the Planck satellite, and galaxy clustering and weak lensing from SDSS. We consider the spherical harmonic power spectra of these probes including all six auto- and cross-correlations along with the associated full gaussian covariance matrix. This provides an integrated treatment o...
The WiggleZ Dark Energy Survey: Final data release and cosmological results
Parkinson, David; Blake, Chris; Poole, Gregory B; Davis, Tamara M; Brough, Sarah; Colless, Matthew; Contreras, Carlos; Couch, Warrick; Croom, Scott; Croton, Darren; Drinkwater, Michael J; Forster, Karl; Gilbank, David; Gladders, Mike; Glazebrook, Karl; Jelliffe, Ben; Jurek, Russell J; Li, I-hui; Madore, Barry; Martin, D Christopher; Pimbblet, Kevin; Pracy, Michael; Sharp, Rob; Wisnioski, Emily; Woods, David; Wyder, Ted K; Yee, H K C
2012-01-01
This paper presents cosmological results from the final data release of the WiggleZ Dark Energy Survey. We perform full analyses of different cosmological models using the WiggleZ power spectra measured at z=0.22, 0.41, 0.60, and 0.78, combined with other cosmological datasets. The limiting factor in this analysis is the theoretical modelling of the galaxy power spectrum, including non-linearities, galaxy bias, and redshift-space distortions. In this paper we assess several different methods for modelling the theoretical power spectrum, testing them against the Gigaparsec WiggleZ simulations (GiggleZ). We fit for a base set of 6 cosmological parameters, {Omega_b h^2, Omega_CDM h^2, H_0, tau, A_s, n_s}, and 5 supplementary parameters {n_run, r, w, Omega_k, sum m_nu}. In combination with the Cosmic Microwave Background (CMB), our results are consistent with the LambdaCDM concordance cosmology, with a measurement of the matter density of Omega_m =0.29 +/- 0.016 and amplitude of fluctuations sigma_8 = 0.825 +/- 0...
Canu, Federico A.
2013-01-01
The Kyoto commitment period has come to an end in 2012, and new discussions have started on how the new commitment period and its market mechanism will be shaped. It seems like the CDM will continue to exist in the future, either as a parallel system to the new one, or as an integrated part. The thesis addresses how the CDM’s environmental integrity and the uneven country participation to the mechanism can be enhanced. The research focuses on the UNFCCC methodology tool to calculate the emiss...
Duality extended Chaplygin cosmologies with a big rip
Chimento, L P; Chimento, Luis P.; Lazkoz, Ruth
2006-01-01
We consider modifications to the Friedmann equation motivated by recent proposals along these lines pursuing an explanation to the observed late time acceleration. Here we show those modifications can be framed within a theory with self-interacting gravity, where the term self-interaction refers here to the presence of functions of $\\rho$ and $p$ in the right hand side of the Einstein equations. We then discuss the construction of the duals of the cosmologies generated within that framework. After that we investigate the modifications required to generate generalized and modified Chaplygin cosmologies and show that their duals belong to a larger family of cosmologies we call extended Chaplygin cosmologies. Finally, by letting the parameters of those models take values not earlier considered in the literature we show some representatives of that family of cosmologies display sudden future singularities, which indicates their behavior is rather different from generalized or modified Chaplygin gas cosmologies. T...
Duality gives rise to Chaplygin cosmologies with a big rip
Chimento, Luis P.; Lazkoz, Ruth
2006-05-01
We consider modifications to the Friedmann equation motivated by recent proposals along these lines pursuing an explanation to the observed late time acceleration. Here we show that these approaches can be framed within a theory with modified gravity, and we discuss the construction of the duals of the cosmologies generated within that framework. We then investigate the modifications required to generate extended, generalized and modified Chaplygin cosmologies, and then show that their duals belong to a larger family of cosmologies we call enlarged Chaplygin cosmologies. Finally, by letting the parameters of these models take values not earlier considered in the literature we show that some representatives of that family of cosmologies display sudden future singularities. This fact indicates that the behaviour of these spacetimes is rather different from that of generalized or modified Chaplygin gas cosmologies. This reinforces the idea that modifications of gravity can be responsible for unexpected evolutionary features in the universe.
Superbounce and loop quantum cosmology ekpyrosis from modified gravity
Oikonomou, V. K.
2015-09-01
As is known, in modified cosmological theories of gravity many of the cosmologies which could not be generated by standard Einstein gravity, can be consistently described by theories. Using known reconstruction techniques, we investigate which theories can lead to a Hubble parameter describing two types of cosmological bounces, the superbounce model, related to supergravity and non-supersymmetric models of contracting ekpyrosis and also the Loop Quantum Cosmology modified ekpyrotic model. Since our method is an approximate method, we investigate the problem at large and small curvatures. As we evince, both models yield power law reconstructed gravities, with the most interesting new feature being that both lead to accelerating cosmologies, in the large curvature approximation. The mathematical properties of the some Friedmann-Robertson-Walker spacetimes , that describe superbounce-like cosmologies are also pointed out, with regards to the group of curvature collineations.
Sustainable waste management in Africa through CDM projects
International Nuclear Information System (INIS)
Highlights: ► This is a compendium on GHG reductions via improved waste strategies in Africa. ► This note provides a strategic framework for Local Authorities in Africa. ► Assists LAs to select Zero Waste scenarios and achieve sustained GHG reduction. - Abstract: Only few Clean Development Mechanism (CDM) projects (traditionally focussed on landfill gas combustion) have been registered in Africa if compared to similar developing countries. The waste hierarchy adopted by many African countries clearly shows that waste recycling and composting projects are generally the most sustainable. This paper undertakes a sustainability assessment for practical waste treatment and disposal scenarios for Africa and makes recommendations for consideration. The appraisal in this paper demonstrates that mechanical biological treatment of waste becomes more financially attractive if established through the CDM process. Waste will continue to be dumped in Africa with increasing greenhouse gas emissions produced, unless industrialised countries (Annex 1) fund carbon emission reduction schemes through a replacement to the Kyoto Protocol. Such a replacement should calculate all of the direct and indirect carbon emission savings and seek to promote public–private partnerships through a concerted support of the informal sector.
Relativistic weak lensing from a fully non-linear cosmological density field
Thomas, D. B.; Bruni, M.; Wands, D.
2015-09-01
In this paper we examine cosmological weak lensing on non-linear scales and show that there are Newtonian and relativistic contributions and that the latter can also be extracted from standard Newtonian simulations. We use the post-Friedmann formalism, a post-Newtonian type framework for cosmology, to derive the full weak-lensing deflection angle valid on non-linear scales for any metric theory of gravity. We show that the only contributing term that is quadratic in the first order deflection is the expected Born correction and lens-lens coupling term. We use this deflection angle to analyse the vector and tensor contributions to the E- and B- mode cosmic shear power spectra. In our approach, once the gravitational theory has been specified, the metric components are related to the matter content in a well-defined manner. Specifying General Relativity, we write down a complete set of equations for a GR+ΛCDM universe for computing all of the possible lensing terms from Newtonian N-body simulations. We illustrate this with the vector potential and show that, in a GR+ΛCDM universe, its contribution to the E-mode is negligible with respect to that of the conventional Newtonian scalar potential, even on non-linear scales. Thus, under the standard assumption that Newtonian N-body simulations give a good approximation of the matter dynamics, we show that the standard ray tracing approach gives a good description for a ΛCDM cosmology.
Philosophical Roots of Cosmology
Ivanovic, M.
2008-10-01
We shall consider the philosophical roots of cosmology in the earlier Greek philosophy. Our goal is to answer the question: Are earlier Greek theories of pure philosophical-mythological character, as often philosophers cited it, or they have scientific character. On the bases of methodological criteria, we shall contend that the latter is the case. In order to answer the question about contemporary situation of the relation philosophy-cosmology, we shall consider the next question: Is contemporary cosmology completely independent of philosophical conjectures? The answer demands consideration of methodological character about scientific status of contemporary cosmology. We also consider some aspects of the relation contemporary philosophy-cosmology.
Cosmic expansion and structure formation in running vacuum cosmologies
Basilakos, Spyros
2015-01-01
We investigate the dynamics of the FLRW flat cosmological models in which the vacuum energy varies with redshift. A particularly well motivated model of this type is the so-called quantum field vacuum, in which both kind of terms $H^{2}$ and constant appear in the effective dark energy density affecting the evolution of the main cosmological functions at the background and perturbation levels. Specifically, it turns out that the functional form of the quantum vacuum endows the vacuum energy of a mild dynamical evolution which could be observed nowadays and appears as dynamical dark energy. Interestingly, the low-energy behaviour is very close to the usual $\\Lambda$CDM model, but it is by no means identical. Finally, within the framework of the quantum field vacuum we generalize the large scale structure properties, namely growth of matter perturbations, cluster number counts and spherical collapse model.
Cosmological wormholes in $f(R)$ theories of gravity
Bahamonde, Sebastian; Pavlovic, Petar; Sossich, Marko
2016-01-01
Motivated by recent proposals of possible wormhole existence in galactic halos, we analyse the cosmological evolution of wormhole solutions in modified $f(R)$ gravity. We construct a dynamical wormhole that asymptotically approaches FLRW universe, with supporting material going to the perfect isotropic fluid described by the equation of state for radiation and matter dominated universe respectively. Our analysis is based on an approximation of a small wormhole - a wormhole that can be treated as matched with the FLRW metric at some radial coordinate much smaller than the Hubble radius, so that cosmological boundary conditions are satisfied. With a special interest in viable wormhole solutions, we refer to the results of reconstruction procedure and use $f(R)$ functions which lead to the experimentally confirmed $\\Lambda$CDM expansion history of the Universe. Solutions we find imply no need for exotic matter near the throat of considered wormholes, while in the limit of $f(R)=R$ this need is always present dur...
A cosmological concordance model with dynamical vacuum term
Energy Technology Data Exchange (ETDEWEB)
Alcaniz, J.S., E-mail: alcaniz@on.br [Observatorio Nacional, Rio de Janeiro, RJ (Brazil); Borges, H.A., E-mail: humberto@ufba.br [Instituto de Fisica, Universidade Federal da Bahia, Salvador, BA (Brazil); Carneiro, S., E-mail: saulo.carneiro@pq.cnpq.br [Instituto de Fisica, Universidade Federal da Bahia, Salvador, BA (Brazil); Fabris, J.C., E-mail: fabris@pq.cnpq.br [Departamento de Fisica, Universidade Federal do Espirito Santo, Vitoria, ES (Brazil); Pigozzo, C., E-mail: kssiobr@gmail.com [Instituto de Fisica, Universidade Federal da Bahia, Salvador, BA (Brazil); Zimdahl, W., E-mail: zimdahl@online.de [Departamento de Fisica, Universidade Federal do Espirito Santo, Vitoria, ES (Brazil)
2012-09-17
We demonstrate that creation of dark-matter particles at a constant rate implies the existence of a cosmological term that decays linearly with the Hubble rate. We discuss the cosmological model that arises in this context and test it against observations of the first acoustic peak in the cosmic microwave background (CMB) anisotropy spectrum, the Hubble diagram for supernovas of type Ia (SNIa), the distance scale of baryonic acoustic oscillations (BAO) and the distribution of large scale structures (LSS). We show that a good concordance is obtained, albeit with a higher value of the present matter abundance than in the {Lambda}CDM model. We also comment on general features of the CMB anisotropy spectrum and on the cosmic coincidence problem.
Evidence for Matter Bounce Cosmology in Low Redshift Observations
Cai, Yi-Fu; Easson, Damien A; Wang, Dong-Gang
2015-01-01
The Matter Bounce scenario allows for a sizable parameter space where cosmological fluctuations originally exit the Hubble radius when the background energy density was small. In this scenario and its extended versions, the low energy degrees of freedom are likely responsible for the statistical properties of the cosmic microwave background (CMB) power spectrum at large length scales. An interesting consequence is that these modes might be observable only at relatively late times. Therefore low redshift observations could provide evidence for, or even falsify, various bouncing models. We provide an example where a recently hinted potential deviation from $\\Lambda$-Cold-Dark-Matter ($\\Lambda$CDM) cosmology results from a dark matter (DM) and dark energy (DE) interaction. The same interaction allows Matter Bounce models to generate a red tilt for the primordial curvature perturbations in corroboration with CMB experiments.
Flowing with Time: a New Approach to Nonlinear Cosmological Perturbations
Pietroni, Massimo
2008-01-01
Nonlinear effects are crucial in order to compute the cosmological matter power spectrum to the accuracy required by future generation surveys. Here, a new approach is presented, in which the power spectrum and the bispectrum are obtained -at any redshift and for any momentum scale- by integrating a coupled system of differential equations. The solution of the equations corresponds, in perturbation theory, to the summation of an infinite class of corrections. Compared to other resummation frameworks, the scheme discussed here is particularly suited to cosmologies other than LambdaCDM, such as those based on modifications of gravity and those containing massive neutrinos. As a first application, we compute the Baryonic Acoustic Oscillation feature of the power spectrum, and compare the results with perturbation theory, the halo model, and N-body simulations. The density-velocity and velocity-velocity power spectra are also computed, showing that they are much less contaminated by nonlinearities than the densit...
Krioukov, Dmitri; Sinkovits, Robert S; Rideout, David; Meyer, David; Boguna, Marian
2012-01-01
Causal sets are an approach to quantum gravity in which the causal structure of spacetime plays a fundamental role. The causal set is a quantum network which underlies the fabric of spacetime. The nodes in this network are tiny quanta of spacetime, with two such quanta connected if they are causally related. Here we show that the structure of these networks in de Sitter spacetime, such as our accelerating universe, is remarkably similar to the structure of complex networks -- the brain or the Internet, for example. Specifically, we show that the node degree distribution of causal sets in de Sitter spacetime is described by a power law with exponent 2, similar to many complex networks. Quantifying the differences between the causal set structure in de Sitter spacetime and in the real universe, we find that since the universe today is relatively young, its power-law exponent is not 2 but 3/4, yet exponent 2 is currently emerging. Finally, we show that as a consequence of a simple geometric duality, the growth d...
Cosmological tests with the FSRQ gamma-ray luminosity function
Zeng, Houdun; Melia, Fulvio; Zhang, Li
2016-11-01
The extensive catalogue of gamma-ray selected flat-spectrum radio quasars (FSRQs) produced by Fermi during a four-year survey has generated considerable interest in determining their gamma-ray luminosity function (GLF) and its evolution with cosmic time. In this paper, we introduce the novel idea of using this extensive database to test the differential volume expansion rate predicted by two specific models, the concordance Λ cold dark matter (ΛCDM) and Rh = ct cosmologies. For this purpose, we use two well-studied formulations of the GLF, one based on pure luminosity evolution (PLE) and the other on a luminosity-dependent density evolution (LDDE). Using a Kolmogorov-Smirnov test on one-parameter cumulative distributions (in luminosity, redshift, photon index and source count), we confirm the results of earlier works showing that these data somewhat favour LDDE over PLE; we show that this is the case for both ΛCDM and Rh = ct. Regardless of which GLF one chooses, however, we also show that model selection tools very strongly favour Rh = ct over ΛCDM. We suggest that such population studies, though featuring a strong evolution in redshift, may none the less be used as a valuable independent check of other model comparisons based solely on geometric considerations.
Late time cosmic acceleration from natural infrared cutoff
Gorji, Mohammad Ali
2016-09-01
In this paper, inspired by the ultraviolet deformation of the Friedmann-Lemaître-Robertson-Walker geometry in loop quantum cosmology, we formulate an infrared-modified cosmological model. We obtain the associated deformed Friedmann and Raychaudhuri equations and we show that the late time cosmic acceleration can be addressed by the infrared corrections. As a particular example, we applied the setup to the case of matter dominated universe. This model has the same number of parameters as ΛCDM, but a dynamical dark energy generates in the matter dominated era at the late time. According to our model, as the universe expands, the energy density of the cold dark matter dilutes and when the Hubble parameter approaches to its minimum, the infrared effects dominate such that the effective equation of state parameter smoothly changes from weff = 0 to weff = - 2. Interestingly and nontrivially, the unstable de Sitter phase with weff = - 1 is corresponding to Ωm =Ωd = 0.5 and the universe crosses the phantom divide from the quintessence phase with weff > - 1 and Ωm >Ωd to the phantom phase with weff < - 1 and Ωm <Ωd which shows that the model is observationally viable. The results show that the universe finally ends up in a big rip singularity for a finite time proportional to the inverse of the minimum of the Hubble parameter. Moreover, we consider the dynamical stability of the model and we show that the universe starts from the matter dominated era at the past attractor with weff = 0 and ends up in a future attractor at the big rip with weff = - 2.
Late time cosmic acceleration from natural infrared cutoff
Gorji, Mohammad Ali
2016-09-01
In this paper, inspired by the ultraviolet deformation of the Friedmann-Lemaître-Robertson-Walker geometry in loop quantum cosmology, we formulate an infrared-modified cosmological model. We obtain the associated deformed Friedmann and Raychaudhuri equations and we show that the late time cosmic acceleration can be addressed by the infrared corrections. As a particular example, we applied the setup to the case of matter dominated universe. This model has the same number of parameters as ΛCDM, but a dynamical dark energy generates in the matter dominated era at the late time. According to our model, as the universe expands, the energy density of the cold dark matter dilutes and when the Hubble parameter approaches to its minimum, the infrared effects dominate such that the effective equation of state parameter smoothly changes from weff = 0 to weff = - 2. Interestingly and nontrivially, the unstable de Sitter phase with weff = - 1 is corresponding to Ωm =Ωd = 0.5 and the universe crosses the phantom divide from the quintessence phase with weff > - 1 and Ωm >Ωd to the phantom phase with weff ends up in a big rip singularity for a finite time proportional to the inverse of the minimum of the Hubble parameter. Moreover, we consider the dynamical stability of the model and we show that the universe starts from the matter dominated era at the past attractor with weff = 0 and ends up in a future attractor at the big rip with weff = - 2.
Cosmological test using strong gravitational lensing systems
Yuan, C C
2015-01-01
As one of the probes of universe, strong gravitational lensing systems allow us to compare different cosmological models and constrain vital cosmological parameters. This purpose can be reached from the dynamic and geometry properties of strong gravitational lensing systems, for instance, time-delay $\\Delta\\tau$ of images, the velocity dispersion $\\sigma$ of the lensing galaxies and the combination of these two effects, $\\Delta\\tau/\\sigma^2$. In this paper, in order to carry out one-on-one comparisons between $\\Lambda$CDM universe and $R_h=ct$ universe, we use a sample containing 36 strong lensing systems with the measurement of velocity dispersion from the SLACS and LSD survey. Concerning the time-delay effect, 12 two-image lensing systems with $\\Delta\\tau$ are also used. In addition, Monte Carlo (MC) simulations are used to compare the efficiency of the three methods as mentioned above. From simulations, we estimate the number of lenses required to rule out one model at the $99.7\\%$ confidence level. Compar...
Holographic Dark Energy with Cosmological Constant
Hu, Yazhou; Li, Nan; Zhang, Zhenhui
2015-01-01
Inspired by the multiverse scenario, we study a heterotic dark energy model in which there are two parts, the first being the cosmological constant and the second being the holographic dark energy, thus this model is named the $\\Lambda$HDE model. By studying the $\\Lambda$HDE model theoretically, we find that the parameters $c$ and $\\Omega_{hde}$ are divided into a few domains in which the fate of the universe is quite different. We investigate dynamical behaviors of this model, and especially the future evolution of the universe. We perform fitting analysis on the cosmological parameters in the $\\Lambda$HDE model by using the recent observational data. We find the model yields $\\chi^2_{\\rm min}=426.27$ when constrained by Planck+SNLS3+BAO+HST, comparable to the results of the HDE model (428.20) and the concordant $\\Lambda$CDM model (431.35). At 68.3\\% CL, we obtain $-0.07<\\Omega_{\\Lambda0}<0.68$ and correspondingly $0.04<\\Omega_{hde0}<0.79$, implying at present there is considerable degeneracy bet...
Cosmological Perturbations in Extended Massive Gravity
Gumrukcuoglu, A Emir; Lin, Chunshan; Mukohyama, Shinji; Trodden, Mark
2013-01-01
We study cosmological perturbations around self-accelerating solutions to two extensions of nonlinear massive gravity: the quasi-dilaton theory and the mass-varying theory. We examine stability of the cosmological solutions, and the extent to which the vanishing of the kinetic terms for scalar and vector perturbations of self-accelerating solutions in massive gravity is generic when the theory is extended. We find that these kinetic terms are in general non-vanishing in both extensions, though there are constraints on the parameters and background evolution from demanding that they have the correct sign. In particular, the self-accelerating solutions of the quasi-dilaton theory are always unstable to scalar perturbations with wavelength shorter than the Hubble length.
Axion-dilaton cosmology and dark energy
Energy Technology Data Exchange (ETDEWEB)
Catena, R.; Moeller, J.
2007-09-15
We discuss a class of flat FRW cosmological models based on D=4 axion-dilaton gravity universally coupled to cosmological background fluids. In particular, we investigate the possibility of recurrent acceleration, which was recently shown to be generically realized in a wide class of axion-dilaton models, but in absence of cosmological background fluids. We observe that, once we impose the existence of radiation - and matter - dominated earlier stages of cosmic evolution, the axion-dilaton dynamics is altered significantly with respect to the case of pure axion-dilaton gravity. During the matter dominated epoch the scalar fields remain either frozen, due to the large expansion rate, or enter a cosmological scaling regime. In both cases, oscillations of the effective equation of state around the acceleration boundary value are impossible. Models which enter an oscillatory stage in the low redshift regime, on the other hand, are disfavored by observations. We also comment on the viability of the axion-dilaton system as a candidate for dynamical dark energy. In a certain subclass of models, an intermediate scaling regime is succeeded by eternal acceleration. We also briefly discuss the issue of dependence on initial conditions. (orig.)
International Nuclear Information System (INIS)
Greenhouse gas emissions due to human activities are the main contributors to global climate change, a problem that should not be ignored. Through the clean development mechanism (CDM) introduced under the Kyoto Protocol, developing countries are able to earn certified emission reduction (CER) credits through a myriad of emission reduction projects. This study aims to explore the potential of implementing CDM projects in the construction and built environment (C and BE) industry, which has been criticized for not only consuming an enormous amount of resources, but also for contributing to adverse environmental health. In this research, we limit the boundary of the C and BE industry to include the planning, procurement, construction, occupation and refurbishment/demolition phases of a project's life cycle. Surveys and in-depth follow-up interviews with experts have generated useful insights pertaining to CDM potential and its adaptation into the C and BE industry. From this foundation, this paper evaluates the current obstacles to CDM and presents feasible suggestions to increase CDM projects related to the C and BE industry. - Highlights: • We review the development and limitation of CDM relates to the construction and built environment (C and BE) industry. • We obtain experts' opinions on the feasibility of CDM in the C and BE industry. • Validation, monitoring, verification and additionality of CDM projects are crucial. • Experts agreed that most of our suggestions are feasible in principle
Assessing Usefulness. Do Stakeholders Regard the CDM's SD Tool as Practicial?
DEFF Research Database (Denmark)
Olsen, Karen Holm; Fenhann, Jørgen Villy; Hinostroza, Miriam L.;
implementation of this requirement. The independent High-Level Panel on the CDM Policy Dialogue has also considered the need for improvement. Subsequently the Conference of the Parties serving as the meetings of the Parties to the Kyoto Protocol (CMP) 7 at Durban called on the CDM Executive Board to develop...
Energy Technology Data Exchange (ETDEWEB)
Bousso, Raphael
2005-01-25
We study conditions for the existence of asymptotic observables in cosmology. With the exception of de Sitter space, the thermal properties of accelerating universes permit arbitrarily long observations, and guarantee the production of accessible states of arbitrarily large entropy. This suggests that some asymptotic observables may exist, despite the presence of an event horizon. Comparison with decelerating universes shows surprising similarities: Neither type suffers from the limitations encountered in de Sitter space, such as thermalization and boundedness of entropy. However, we argue that no realistic cosmology permits the global observations associated with an S-matrix.
Radiation-dominated area metric cosmology
Schuller, Frederic P
2007-01-01
We provide further crucial support for a refined, area metric structure of spacetime. Based on the solution of conceptual issues, such as the consistent coupling of fermions and the covariant identification of radiation fields on area metric backgrounds, we show that the radiation-dominated epoch of area metric cosmology is equivalent to that epoch in standard Einstein cosmology. This ensures, in particular, successful nucleosynthesis. This surprising result complements the previously derived prediction of a small late-time acceleration of an area metric universe.
Non-flat power spectra in the CDM model
Semig, L V; Semig, Lutz V; Mueller, Volker
1995-01-01
Standard inflation with one scalar field produces primordial perturbations with a nearly flat ('Harrison-Zeldovich') power spectrum. Here we consider first, a double inflation spectrum, and second, a massive scalar field with an interaction potential which mimics an early quartic interaction, but fading away at a characteristic scale. We solve numerically the linear perturbation equations with initial conditions due to scalar field quantum fluctuations at the initial horizon crossing. The resulting power spectra are shown to be non-flat, exhibiting either a break or a valley. Using the transfer function of cold dark matter model we study the influence of the shape of primordial power spectra on observations of large scale structure in the universe. We compare the power spectra in redshift space with reconstructed power spectra from the IRAS catalogue. Further we discuss the variances of galaxy counts in cells, and the mass function of galaxy clusters. Comparison with standard CDM demonstrates the advantages a...
Cosmological Simulations of Normal-Branch Braneworld Gravity
Schmidt, Fabian
2009-01-01
We introduce a cosmological model based on the normal branch of DGP braneworld gravity with a smooth dark energy component on the brane. The expansion history in this model is identical to LambdaCDM, thus evading all geometric constraints on the DGP cross-over scale r_c. This model can serve as a first approximation to more general braneworld models whose cosmological solutions have not been obtained yet. We study the formation of large scale structure in this model in the linear and non-linear regime using N-body simulations for different values of r_c. The simulations use the code presented in (F.S., arXiv:0905.0858) and solve the full non-linear equation for the brane-bending mode in conjunction with the usual gravitational dynamics. The brane-bending mode is attractive rather than repulsive in the DGP normal branch, hence the sign of the modified gravity effects is reversed compared to those presented in arXiv:0905.0858. We compare the simulation results with those of ordinary LambdaCDM simulations run us...
Dynamical history of the Local Group in ΛCDM
Banik, Indranil; Zhao, Hongsheng
2016-06-01
The positions and velocities of galaxies in the Local Group (LG) measure the gravitational field within it. This is mostly due to the Milky Way (MW) and Andromeda (M31). We constrain their masses using distance and radial velocity (RV) measurements of 32 LG galaxies. To do this, we follow the trajectories of many simulated particles starting on a pure Hubble flow at redshift 9. For each observed galaxy, we obtain a trajectory which today is at the same position. Its final velocity is the model prediction for the velocity of that galaxy. Unlike previous simulations based on spherical symmetry, ours are axisymmetric and include gravity from Centaurus A. We find the total LG mass is {4.33^{+0.37}_{-0.32}× {10}^{12} M_{⊙}}, with 0.14 ± 0.07 of this being in the MW. We approximately account for IC 342, M81, the Great Attractor and the Large Magellanic Cloud. No plausible set of initial conditions yields a good match to the RVs of our sample of LG galaxies. Observed RVs systematically exceed those predicted by the best-fitting Lambda Cold Dark Matter (ΛCDM) model, with a typical disagreement of {45.1^{+7.0}_{-5.7}} km s-1 and a maximum of 110 ± 13 km s-1 for DDO 99. Interactions between LG dwarf galaxies cannot easily explain this. One possibility is a past close flyby of the MW and M31. This arises in some modified gravity theories but not in ΛCDM. Gravitational slingshot encounters of material in the LG with either of these massive fast-moving galaxies could plausibly explain why some non-satellite LG galaxies are moving away from us even faster than a pure Hubble flow.
A Comparative Study on the Implementation of CDM Projects in India
Institute of Scientific and Technical Information of China (English)
Jiang Xiaoyi
2012-01-01
Since the Clean Development Mechanism （CDM） under the Kyoto Protocol was initiated, China and India have overwhelmingly led other developing countries regarding CDM projects development. A comparative study of the CDM in India and China is conducted as there are many similarities between both India and China with regard to the CDM implementation due to the fact that India is another major developing country with a large population and a potential source of GHG emissions rivaling China in the near future. Through examining the development of and legal issues for CDM projects in India, its experience and les- sons regarding developing and managing CDM projects that China can critically learn are discussed.
EU-MENA energy technology transfer under the CDM: Israel as a frontrunner?
International Nuclear Information System (INIS)
The majority of the Middle East and North Africa (MENA) countries possess substantial potential for the implementation of CDM projects. Abatement of Greenhouse Gas (GHG) emissions can mainly be achieved through utilizing the abundant Renewable Energy Sources (RES) in the region and the implementation of Energy Efficiency (ENEF) measures. However, most of the MENA countries have a limited track record as regards CDM projects in the pipeline comparing to the major CDM-players, like Asia-Pacific regions and Latin America. In the above framework, this paper investigates the current status of CDM in the MENA region and the related perspectives for further diffusion of the CDM though the elaboration of a Strengths-Weaknesses-Opportunities and Threats (SWOT) Analysis. Particular emphasis is laid on the case of Israel, which seems to make an exception to the rule, since it hosts most projects in the region and dominates among the MENA countries.
Cosmological parallax-distance formula
Singal, Ashok K.
2015-09-01
The standard cosmological parallax-distance formula, as found in the literature, including text-books and reference books on cosmology, requires a correction. This correction stems from the fact that in the standard text-book derivation it has been ignored that any chosen baseline in a gravitationally bound system does not partake in the cosmological expansion. Though the correction is available in the literature for some time, the text-books still continue to use the older, incorrect formula, and its full implications are not yet fully realized. Apart from providing an alternate correct, closed-form expression that is more suitable and convenient for computations for certain limiting cases of FRW () world models, we also demonstrate how one can compute parallax distance for the currently favored flat-space accelerating-universe (, ) cosmologies. Further, we show that the correction in parallax distance at large redshifts could amount to a factor of three or even more. Moreover, even in an infinite universe the parallax distance does not increase indefinitely with redshift and that even the farthest possible observable point may have a finite parallax angle, a factor that needs to be carefully taken into account when using distant objects as the background field against which the parallax of a foreground object is to be measured. Some other complications that could arise in parallax measurements of a distant source, like that due to the deflection of incoming light by the gravitation field of the Sun and other planetary bodies in the solar system, are pointed out.
Cosmological models and stability
Andersson, Lars
2013-01-01
Principles in the form of heuristic guidelines or generally accepted dogma play an important role in the development of physical theories. In particular, philosophical considerations and principles figure prominently in the work of Albert Einstein. As mentioned in the talk by Jiri Bicak at this conference Einstein formulated the equivalence principle, an essential step on the road to general relativity, during his time in Prague 1911-1912. In this talk, I would like to discuss some aspects of cosmological models. As cosmology is an area of physics where "principles" such as the "cosmological principle" or the "Copernican principle" play a prominent role in motivating the class of models which form part of the current standard model, I will start by comparing the role of the equivalence principle to that of the principles used in cosmology. I will then briefly describe the standard model of cosmology to give a perspective on some mathematical problems and conjectures on cosmological models, which are discussed...
Cosmology and particle physics
International Nuclear Information System (INIS)
This paper comprises the contents of four lectures in which the author illustrates the two-way nature of the interplay between the fields of cosmology and particle physics by focusing on several specifics: a review of the standard cosmology, concentrating on primordial nucleosynthesis; baryogenesis; monopoles; and the case in which a very early first-order phase transition associated with spontaneous symmetry breaking has the potential to explain some very fundamental cosmological facts
Dolgov, A.D.(Novosibirsk State University, Novosibirsk, 630090, Russia)
2002-01-01
Cosmological implications of neutrinos are reviewed. The following subjects are discussed at a different level of scrutiny: cosmological limits on neutrino mass, neutrinos and primordial nucleosynthesis, cosmological constraints on unstable neutrinos, lepton asymmetry of the universe, impact of neutrinos on cosmic microwave radiation, neutrinos and the large scale structure of the universe, neutrino oscillations in the early universe, baryo/lepto-genesis and neutrinos, neutrinos and high ener...
Directory of Open Access Journals (Sweden)
Balbi Amedeo
2013-09-01
Full Text Available Time has always played a crucial role in cosmology. I review some of the aspects of the present cosmological model which are more directly related to time, such as: the definition of a cosmic time; the existence of typical timescales and epochs in an expanding universe; the problem of the initial singularity and the origin of time; the cosmological arrow of time.
Cosmological Constraints from the SDSS maxBCG Cluster Catalog
Energy Technology Data Exchange (ETDEWEB)
Rozo, Eduardo; /CCAPP; Wechsler, Risa H.; /KIPAC, Menlo Park /SLAC; Rykoff, Eli S.; /UC, Santa Barbara; Annis, James T.; /Fermilab; Becker, Matthew R.; /Chicago U. /KICP, Chicago; Evrard, August E.; /Michigan U. /Michigan U., MCTP; Frieman, Joshua A.; /Fermilab /KICP, Chicago /Chicago U.; Hansen, Sarah M.; /UC, Santa Cruz; Hao, Jia; /Michigan U.; Johnston, David E.; /Northwestern U.; Koester, Benjamin P.; /KICP, Chicago /Chicago U.; McKay, Timothy A.; /Michigan U. /Michigan U., MCTP; Sheldon, Erin S.; /Brookhaven; Weinberg, David H.; /CCAPP /Ohio State U.
2009-08-03
We use the abundance and weak lensing mass measurements of the SDSS maxBCG cluster catalog to simultaneously constrain cosmology and the richness-mass relation of the clusters. Assuming a flat {Lambda}CDM cosmology, we find {sigma}{sub 8}({Omega}{sub m}/0.25){sup 0.41} = 0.832 {+-} 0.033 after marginalization over all systematics. In common with previous studies, our error budget is dominated by systematic uncertainties, the primary two being the absolute mass scale of the weak lensing masses of the maxBCG clusters, and uncertainty in the scatter of the richness-mass relation. Our constraints are fully consistent with the WMAP five-year data, and in a joint analysis we find {sigma}{sub 8} = 0.807 {+-} 0.020 and {Omega}{sub m} = 0.265 {+-} 0.016, an improvement of nearly a factor of two relative to WMAP5 alone. Our results are also in excellent agreement with and comparable in precision to the latest cosmological constraints from X-ray cluster abundances. The remarkable consistency among these results demonstrates that cluster abundance constraints are not only tight but also robust, and highlight the power of optically-selected cluster samples to produce precision constraints on cosmological parameters.
Lopez-Corredoira, Martin
2008-01-01
Certain results of observational cosmology cast critical doubt on the foundations of standard cosmology but leave most cosmologists untroubled. Alternative cosmological models that differ from the Big Bang have been published and defended by heterodox scientists; however, most cosmologists do not heed these. This may be because standard theory is correct and all other ideas and criticisms are incorrect, but it is also to a great extent due to sociological phenomena such as the "snowball effect" or "groupthink". We might wonder whether cosmology, the study of the Universe as a whole, is a science like other branches of physics or just a dominant ideology.
López-Corredoira, M.
2009-08-01
Certain results of observational cosmology cast critical doubt on the foundations of standard cosmology but leave most cosmologists untroubled. Alternative cosmological models that differ from the Big Bang have been published and defended by heterodox scientists; however, most cosmologists do not heed these. This may be because standard theory is correct and all other ideas and criticisms are incorrect, but it is also to a great extent due to sociological phenomena such as the ``snowball effect'' or ``groupthink''. We might wonder whether cosmology, the study of the Universe as a whole, is a science like other branches of physics or just a dominant ideology.
Dark Energy and the Cosmological Constant: A Brief Introduction
Harvey, Alex
2009-01-01
The recently observed acceleration of the expansion of the universe is a topic of intense interest. The favoured causes are the "cosmological constant" or "dark energy". The former, which appears in the Einstein equations as the term [lambda]g[subscript [mu]v], provides an extremely simple, well-defined mechanism for the acceleration. However,…
Grand unified models and cosmology
Jeannerot, Rachel
2006-01-01
The cosmological consequences of particle physics grand unified theories (GUTs) are studied. Cosmological models are implemented in realistic particle physics models. Models consistent from both particle physics and cosmological considerations are selected. (...)
The supernova cosmology cookbook: Bayesian numerical recipes
Karpenka, N V
2015-01-01
Theoretical and observational cosmology have enjoyed a number of significant successes over the last two decades. Cosmic microwave background measurements from the Wilkinson Microwave Anisotropy Probe and Planck, together with large-scale structure and supernova (SN) searches, have put very tight constraints on cosmological parameters. Type Ia supernovae (SNIa) played a central role in the discovery of the accelerated expansion of the Universe, recognised by the Nobel Prize in Physics in 2011. The last decade has seen an enormous increase in the amount of high quality SN observations, with SN catalogues now containing hundreds of objects. This number is expected to increase to thousands in the next few years, as data from next-generation missions, such as the Dark Energy Survey and Large Synoptic Survey Telescope become available. In order to exploit the vast amount of forthcoming high quality data, it is extremely important to develop robust and efficient statistical analysis methods to answer cosmological q...
Multi-scale gravity and cosmology
Calcagni, Gianluca
2013-01-01
The gravitational dynamics and cosmological implications of three classes of recently introduced multi-scale spacetimes (with, respectively, ordinary, weighted and q-derivatives) are discussed. These spacetimes are non-Riemannian: the metric structure is accompanied by an independent measure-differential structure with the characteristics of a multi-fractal, namely, different dimensionality at different scales and, at ultra-short distances, a discrete symmetry known as discrete scale invariance. Under this minimal paradigm, five general features arise: (a) the big-bang singularity can be replaced by a finite bounce, (b) the cosmological constant problem is reinterpreted, since accelerating phases can be mimicked by the change of geometry with the time scale, without invoking a slowly rolling scalar field, (c) the discreteness of geometry at Planckian scales can leave an observable imprint of logarithmic oscillations in cosmological spectra and (d) give rise to an alternative mechanism to inflation or (e) to a...
Statefinder diagnostic in a torsion cosmology
Li, Xin-zhou; Xi, Ping
2009-01-01
We apply the statefinder diagnostic to the torsion cosmology, in which an accounting for the accelerated universe is considered in term of a Riemann-Cartan geometry: dynamic scalar torsion. We find that there are some typical characteristic of the evolution of statefinder parameters for the torsion cosmology that can be distinguished from the other cosmological models. Furthermore, we also show that statefinder diagnostic has a direct bearing on the critical points. The statefinder diagnostic divides the torsion parameter $a_1$ into differential ranges, which is in keeping with the requirement of dynamical analysis. In addition, we fit the scalar torsion model to ESSENCE supernovae data and give the best fit values of the model parameters.
Dissipative or Conservative cosmology with dark energy ?
Szydlowski, M; Hrycyna, Orest; Szydlowski, Marek
2006-01-01
All evolutional paths for all admissible initial conditions of FRW cosmological models with dissipative dust fluid (described by dark matter, baryonic matter and dark energy) are analysed using dynamical system approach. With that approach, one is able to see how generic the class of solutions leading to the desired property -- acceleration -- is. The theory of dynamical systems also offers a possibility of investigating all possible solutions and their stability with tools of Newtonian mechanics of a particle moving in 1D potential which is parametrised by the cosmological scale factor. We demonstrate that flat cosmology with bulk viscosity can be treated as a conservative system with a potential function of the Chaplygin gas type. We characterise the class of dark energy models that admit late time de Sitter attractor solution in terms of the potential function of corresponding conservative system. We argue that inclusion of dissipation effects makes the model more realistic because of its structural stabil...
The intrinsic matter bispectrum in ΛCDM
Tram, Thomas; Fidler, Christian; Crittenden, Robert; Koyama, Kazuya; Pettinari, Guido W.; Wands, David
2016-05-01
We present a fully relativistic calculation of the matter bispectrum at second order in cosmological perturbation theory assuming a Gaussian primordial curvature perturbation. For the first time we perform a full numerical integration of the bispectrum for both baryons and cold dark matter using the second-order Einstein-Boltzmann code, SONG. We review previous analytical results and provide an improved analytic approximation for the second-order kernel in Poisson gauge which incorporates Newtonian nonlinear evolution, relativistic initial conditions, the effect of radiation at early times and the cosmological constant at late times. Our improved kernel provides a percent level fit to the full numerical result at late times for most configurations, including both equilateral shapes and the squeezed limit. We show that baryon acoustic oscillations leave an imprint in the matter bispectrum, making a significant impact on squeezed shapes.
Tilted CDM versus WDM in the Subgalactic Scuffle
Bullock, J S
2001-01-01
Although the currently favored cold dark matter plus cosmological constant model (LCDM) has proven to be remarkably successful on large scales, on subgalactic scales it faces some potentially fatal difficulties; these include over-producing dwarf satellite galaxies and predicting excessive central densities in dark halos. Among the most natural cosmological solutions to these problems is to replace cold dark matter with a warm species (LWDM). The warm component acts to reduce the small-scale power, resulting in fewer galactic subhalos and lower halo central densities. An alternative model with a mild ``tilt'' in the inflationary power spectrum (TLCDM; n =0.9) similarly reduces the central densities of dark halos, although the substructure abundance remains relatively high. Here I argue that because dwarf galaxy formation should be suppressed in the presence of a strong ionizing background, favored LWDM models will generally under-predict the observed abundance of dwarf galaxies. The satellite count for TLCDM ...
The Intrinsic Matter Bispectrum in $\\Lambda$CDM
Tram, Thomas; Crittenden, Robert; Koyama, Kazuya; Pettinari, Guido W; Wands, David
2016-01-01
We present a fully relativistic calculation of the matter bispectrum at second order in cosmological perturbation theory assuming a Gaussian primordial curvature perturbation. For the first time we perform a full numerical integration of the bispectrum for both baryons and cold dark matter using the second-order Einstein-Boltzmann code, SONG. We review previous analytical results and provide an improved analytic approximation for the second-order kernel in Poisson gauge which incorporates Newtonian nonlinear evolution, relativistic initial conditions, the effect of radiation at early times and the cosmological constant at late times. Our improved kernel provides a percent level fit to the full numerical result at late times for most configurations, including both equilateral shapes and the squeezed limit. We show that baryon acoustic oscillations leave an imprint in the matter bispectrum, making a significant impact on squeezed shapes.
Non-linear structure formation in the `Running FLRW' cosmological model
Bibiano, Antonio; Croton, Darren J.
2016-07-01
We present a suite of cosmological N-body simulations describing the `Running Friedmann-Lemaïtre-Robertson-Walker' (R-FLRW) cosmological model. This model is based on quantum field theory in a curved space-time and extends Lambda cold dark matter (ΛCDM) with a time-evolving vacuum density, Λ(z), and time-evolving gravitational Newton's coupling, G(z). In this paper, we review the model and introduce the necessary analytical treatment needed to adapt a reference N-body code. Our resulting simulations represent the first realization of the full growth history of structure in the R-FLRW cosmology into the non-linear regime, and our normalization choice makes them fully consistent with the latest cosmic microwave background data. The post-processing data products also allow, for the first time, an analysis of the properties of the halo and sub-halo populations. We explore the degeneracies of many statistical observables and discuss the steps needed to break them. Furthermore, we provide a quantitative description of the deviations of R-FLRW from ΛCDM, which could be readily exploited by future cosmological observations to test and further constrain the model.
Colliders as a simultaneous probe of supersymmetric dark matter and Terascale cosmology
Energy Technology Data Exchange (ETDEWEB)
Barenboim, Gabriela; /Valencia U.; Lykken, Joseph D.; /Fermilab
2006-08-01
Terascale supersymmetry has the potential to provide a natural explanation of the dominant dark matter component of the standard {Lambda}CDM cosmology. However once we impose the constraints on minimal supersymmetry parameters from current particle physics data, a satisfactory dark matter abundance is no longer prima facie natural. This Neutralino Tuning Problem could be a hint of nonstandard cosmology during and/or after the Terascale era. To quantify this possibility, we introduce an alternative cosmological benchmark based upon a simple model of quintessential inflation. This benchmark has no free parameters, so for a given supersymmetry model it allows an unambiguous prediction of the dark matter relic density. As a example, we scan over the parameter space of the CMSSM, comparing the neutralino relic density predictions with the bounds from WMAP. We find that the WMAP-allowed regions of the CMSSM are an order of magnitude larger if we use the alternative cosmological benchmark, as opposed to {Lambda}CDM. Initial results from the CERN Large Hadron Collider will distinguish between the two allowed regions.
The correlated factors of the uneven performances of the CDM host countries
International Nuclear Information System (INIS)
The Kyoto Protocol’s Clean Development Mechanism (CDM) has experienced a rapid growth. Up to 2010, 2763 projects have been registered, standing for about 433 million ton CO2 equivalent (CO2-eq.) of annual carbon credits. However, the performances of CDM host countries are remarkably unbalanced. Previous literature suggested that economic and investment conditions, energy intensity, energy structure, the share of annual carbon credits from high global warming potential (GWP) green house gas (GHG), capacity and institutional buildings of domestic CDM governance can play important roles in promoting CDM. This quantitative analysis shows that domestic economic and investment conditions are the most decisive factors determining the performance of the CDM host countries. Additionally, the influence of carbon intensity of energy consumption is relatively modest, and energy intensity of GDP as well as the share of annual carbon credits from high GWP GHG is less significant. Moreover, several leading CDM countries are not as successful as they seem to be, when the influences of their vast territories, distinguished economic and investment conditions are excluded. Therefore, to simply transplant the CDM governances of these countries can hardly guarantee that other countries will boost their carbon credit outputs. (letter)
The correlated factors of the uneven performances of the CDM host countries
Zhu, Jinshan
2012-03-01
The Kyoto Protocol’s Clean Development Mechanism (CDM) has experienced a rapid growth. Up to 2010, 2763 projects have been registered, standing for about 433 million ton CO2 equivalent (CO2-eq.) of annual carbon credits. However, the performances of CDM host countries are remarkably unbalanced. Previous literature suggested that economic and investment conditions, energy intensity, energy structure, the share of annual carbon credits from high global warming potential (GWP) green house gas (GHG), capacity and institutional buildings of domestic CDM governance can play important roles in promoting CDM. This quantitative analysis shows that domestic economic and investment conditions are the most decisive factors determining the performance of the CDM host countries. Additionally, the influence of carbon intensity of energy consumption is relatively modest, and energy intensity of GDP as well as the share of annual carbon credits from high GWP GHG is less significant. Moreover, several leading CDM countries are not as successful as they seem to be, when the influences of their vast territories, distinguished economic and investment conditions are excluded. Therefore, to simply transplant the CDM governances of these countries can hardly guarantee that other countries will boost their carbon credit outputs.
New type scalar fields for cosmic acceleration
Energy Technology Data Exchange (ETDEWEB)
Kehagias, A; Pakis, S [Department of Physics, National Technical University of Athens, GR-15773, Zografou, Athens (Greece)
2007-05-15
We present a model where a non-conventional scalar field may act like dark energy and leads to cosmic acceleration. The latter is driven by an appropriate field configuration, which result in an effective cosmological constant. The potential role of such a scalar in the cosmological constant problem is also discussed.