{\\Lambda}CDM cosmology from matter only
Telkamp, Herman
2015-01-01
I discuss a matter-only interpretation of {\\Lambda}CDM cosmology, based on conservation of energy and assuming a Machian definition of inertia. {\\Lambda}CDM cosmology can be linked to a Newtonian cosmic potential, subject to a propagating gravitational horizon. In a matter-only universe where total energy is conserved, Machian inertia related to the evolving potential may cause both deceleration and acceleration of recession.
$\\Lambda$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.
The First Generation of Stars in Lambda-CDM Cosmology
Energy Technology Data Exchange (ETDEWEB)
Gao, Liang; /Durham U. /Garching, Max Planck Inst.; Abel, T.; /KIPAC, Menlo Park; Frenk, C.S.; Jenkins, A.; /Durham U.; Springel, V.; /Garching, Max Planck Inst.; Yoshida,; /Nagoya U.
2006-10-10
We have performed a large set of high-resolution cosmological simulations using smoothed particle hydrodynamics (SPH) to study the formation of the first luminous objects in the {Lambda}CDM cosmology. We follow the collapse of primordial gas clouds in eight early structures and document the scatter in the properties of the first star-forming clouds. Our first objects span formation redshifts from z {approx} 10 to z {approx} 50 and cover an order of magnitude in halo mass. We find that the physical properties of the central star-forming clouds are very similar in all of the simulated objects despite significant differences in formation redshift and environment. This suggests that the formation path of the first stars is largely independent of the collapse redshift; the physical properties of the clouds have little correlation with spin, mass, or assembly history of the host halo. The collapse of proto-stellar objects at higher redshifts progresses much more rapidly due to the higher densities, which accelerates the formation of molecular hydrogen, enhances initial cooling and shortens the dynamical timescales. The mass of the star-forming clouds cover a broad range, from a few hundred to a few thousand solar masses, and exhibit various morphologies: some have disk-like structures which are nearly rotational supported; others form flattened spheroids; still others form bars. All of them develop a single protostellar ''seed'' which does not fragment into multiple objects up to the moment that the central gas becomes optically thick to H{sub 2} cooling lines. At this time, the instantaneous mass accretion rate onto the centre varies significantly from object to object, with disk-like structures having the smallest mass accretion rates. The formation epoch and properties of the star-forming clouds are sensitive to the values of cosmological parameters.
An Accelerating Cosmology Without Dark Energy
Steigman, G; R.C. SANTOS; Lima, J.A.S.
2008-01-01
The negative pressure accompanying gravitationally-induced particle creation can lead to a cold dark matter (CDM) dominated, accelerating Universe (Lima et al. 1996) without requiring the presence of dark energy or a cosmological constant. In a recent study Lima et al. (2008, LSS) demonstrated that particle creation driven cosmological models are capable of accounting for the SNIa observations of the recent transition from a decelerating to an accelerating Universe. Here we test the evolution...
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...
$\\sigma$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...
Observational tests for Λ(t)CDM cosmology
International Nuclear Information System (INIS)
We investigate the observational viability of a class of cosmological models in which the vacuum energy density decays linearly with the Hubble parameter, resulting in a production of cold dark matter particles at late times. Similarly to the flat ΛCDM case, there is only one free parameter to be adjusted by the data in this class of Λ(t)CDM scenarios, namely, the matter density parameter. To perform our analysis we use three of the most recent SNe Ia compilation sets (Union2, SDSS and Constitution) along with the current measurements of distance to the BAO peaks at z = 0.2 and z = 0.35 and the position of the first acoustic peak of the CMB power spectrum. We show that in terms of χ2 statistics both models provide good fits to the data and similar results. A quantitative analysis discussing the differences in parameter estimation due to SNe light-curve fitting methods (SALT2 and MLCS2k2) is studied using the current SDSS and Constitution SNe Ia compilations. A matter power spectrum analysis using the 2dFGRS is also performed, providing a very good concordance with the constraints from the SDSS and Constitution MLCS2k2 data
Cosmological redshift, recession velocities and acceleration measures in FRW cosmologies
Toporensky, A V
2015-01-01
In this methodological note we discuss several topics related to interpretation of some basic cosmological principles. We demonstrate that one of the key points is the usage of synchronous reference frames. The Friedmann-Robertson-Walker one is the most known example of them. We describe how different quantities behave in this frame. Special attention is paid to potentially observable parameters. We discuss different variants for choosing measures of velocity and acceleration representing the Hubble flow, and present illustrative calculations of apparent acceleration in flat $\\Lambda CDM$ model for various epochs. We generalize description of the "tethered" galaxies problem for different velocity measures and equations of state, and illustrate time behavior of velocities and redshifts in the $\\Lambda CDM$ model.
A Comparison of the LVDP and {\\Lambda}CDM Cosmological Models
Akarsu, Özgür; Dereli, Tekin
2012-01-01
arXiv:1202.0495v2 [gr-qc] 8 May 2012 A Comparison of the LVDP and CDM Cosmological Models ¨O zg¨ur Akarsu , Tekin Dereli† Department of Physics, Ko¸c University, 34450 ˙ Istanbul/Turkey. Abstract We compare the cosmological kinematics obtained via our law of linearly varying deceler-ation parameter (LVDP) with the kinematics obtained in the CDM model. We show that the LVDP model is almost indistinguishable from the CDM model up to the near future of our univer...
The mass discrepancy acceleration relation in a ΛCDM context
Di Cintio, Arianna; Lelli, Federico
2016-02-01
The mass discrepancy acceleration relation (MDAR) describes the coupling between baryons and dark matter (DM) in galaxies: the ratio of total-to-baryonic mass at a given radius anticorrelates with the acceleration due to baryons. The MDAR has been seen as a challenge to the Λ cold dark matter (ΛCDM) galaxy formation model, while it can be explained by Modified Newtonian Dynamics. In this Letter, we show that the MDAR arises in a ΛCDM cosmology once observed galaxy scaling relations are taken into account. We build semi-empirical models based on ΛCDM haloes, with and without the inclusion of baryonic effects, coupled to empirically motivated structural relations. Our models can reproduce the MDAR: specifically, a mass-dependent density profile for DM haloes can fully account for the observed MDAR shape, while a universal profile shows a discrepancy with the MDAR of dwarf galaxies with M⋆ < 109.5 M⊙, a further indication suggesting the existence of DM cores. Additionally, we reproduce slope and normalization of the baryonic Tully-Fisher relation (BTFR) with 0.17 dex scatter. These results imply that in ΛCDM (i) the MDAR is driven by structural scaling relations of galaxies and DM density profile shapes, and (ii) the baryonic fractions determined by the BTFR are consistent with those inferred from abundance-matching studies.
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.)
An Accelerating Cosmology Without Dark Energy
Steigman, G; Lima, J A S
2008-01-01
The negative pressure accompanying gravitationally-induced particle creation can lead to a cold dark matter (CDM) dominated, accelerating Universe (Lima et al. 1996) without requiring the presence of dark energy or a cosmological constant. In a recent study Lima et al. (2008, LSS) demonstrated that particle creation driven cosmological models are capable of accounting for the SNIa observations of the recent transition from a decelerating to an accelerating Universe. Here we test the evolution of such models at high redshift using the constraint on z_eq, the redshift of the epoch of matter radiation equality, provided by the WMAP constraints on the early Integrated Sachs-Wolfe effect. Since the contribution of baryons and radiation was ignored in the work of LSS, we include them in our study of this class of models. The parameters of these more realistic models with continuous creation of CDM is tested and constrained at widely-separated epochs (z = z_eq and z = 0) in the evolution of the Universe. This compar...
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
International Nuclear Information System (INIS)
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 c2)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
The mass discrepancy acceleration relation in a $\\Lambda$CDM context
Di Cintio, Arianna
2015-01-01
The mass discrepancy acceleration relation (MDAR) describes the coupling between baryons and dark matter (DM) in galaxies: the ratio of total-to-baryonic mass at a given radius anti-correlates with the acceleration due to baryons. The MDAR has been seen as a challenge to the $\\Lambda$CDM galaxy formation model, while it can be explained by Modified Newtonian Dynamics. In this Letter we show that the MDAR arises in a $\\Lambda$CDM cosmology once observed galaxy scaling relations are taken into account. We build semi-empirical models based on $\\Lambda$CDM haloes, with and without the inclusion of baryonic effects, coupled to empirically motivated structural relations. Our models can reproduce the MDAR: specifically, a mass-dependent density profile for DM haloes can fully account for the observed MDAR shape, while a universal profile shows a discrepancy with the MDAR of dwarf galaxies with $\\rm M^{\\star}$$<$$\\rm10^{9.5}M_{\\odot}$, a further indication suggesting the existence of DM cores. Additionally, we rep...
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.)
An accelerating cosmology without dark energy
International Nuclear Information System (INIS)
The negative pressure accompanying gravitationally-induced particle creation can lead to a cold dark matter (CDM) dominated, accelerating Universe (Lima et al. 1996 [1]) without requiring the presence of dark energy or a cosmological constant. In a recent study, Lima et al. 2008 [2] (LSS) demonstrated that particle creation driven cosmological models are capable of accounting for the SNIa observations [3] of the recent transition from a decelerating to an accelerating Universe, without the need for Dark Energy. Here we consider a class of such models where the particle creation rate is assumed to be of the form Γ = βH+γH0, where H is the Hubble parameter and H0 is its present value. The evolution of such models is tested at low redshift by the latest SNe Ia data provided by the Union compilation [4] and at high redshift using the value of zeq, the redshift of the epoch of matter — radiation equality, inferred from the WMAP constraints on the early Integrated Sachs-Wolfe (ISW) effect [5]. Since the contributions of baryons and radiation were ignored in the work of LSS, we include them in our study of this class of models. The parameters of these more realistic models with continuous creation of CDM are constrained at widely-separated epochs (zeq ≈ 3000 and z ≈ 0) in the evolution of the Universe. The comparison of the parameter values, (β, γ), determined at these different epochs reveals a tension between the values favored by the high redshift CMB constraint on zeq from the ISW and those which follow from the low redshift SNIa data, posing a potential challenge to this class of models. While for β = 0 this conflict is only at ∼< 2σ, it worsens as β increases from zero
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 ...
Generalized Chaplygin gas with $alpha = 0$ and the $Lambda CDM$ cosmological model
Fabris, J C
2004-01-01
The generalized Chaplygin gas model is characterized by the equation of state $p = - frac{A}{rho^alpha}$. It is generally stated that the case $alpha = 0$ is equivalent to a model with cosmological constant and dust ($Lambda CDM$). In this work we show that, if this is true for the background equations, this is not true for the perturbation equations. Hence, the mass spectrum predicted for both models may differ.
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...
Accelerating cosmologies from exponential potentials
International Nuclear Information System (INIS)
It is learnt that exponential potentials of the form V ∼ exp(-2cφ/Mp) arising from the hyperbolic or flux compactification of higher-dimensional theories are of interest for getting short periods of accelerated cosmological expansions. Using a similar potential but derived for the combined case of hyperbolic-flux compactification, we study a four-dimensional flat (or open) FRW cosmologies and give analytic (and numerical) solutions with exponential behavior of scale factors. We show that, for the M-theory motivated potentials, the cosmic acceleration of the universe can be eternal if the spatial curvature of the 4d spacetime is negative, while the acceleration is only transient for a spatially flat universe. We also briefly discuss about the mass of massive Kaluza-Klein modes and the dynamical stabilization of the compact hyperbolic extra dimensions. (author)
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.
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...
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.
Constraints on cold dark matter accelerating cosmologies and cluster formation
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We discuss the properties of homogeneous and isotropic flat cosmologies in which the present accelerating stage is powered only by the gravitationally induced creation of cold dark matter (CCDM) particles (Ωm=1). For some matter creation rates proposed in the literature, we show that the main cosmological functions such as the scale factor of the universe, the Hubble expansion rate, the growth factor, and the cluster formation rate are analytically defined. The best CCDM scenario has only one free parameter and our joint analysis involving baryonic acoustic oscillations + cosmic microwave background (CMB) + SNe Ia data yields Ω-tildem=0.28±0.01 (1σ), where Ω-tildem is the observed matter density parameter. In particular, this implies that the model has no dark energy but the part of the matter that is effectively clustering is in good agreement with the latest determinations from the large-scale structure. The growth of perturbation and the formation of galaxy clusters in such scenarios are also investigated. Despite the fact that both scenarios may share the same Hubble expansion, we find that matter creation cosmologies predict stronger small scale dynamics which implies a faster growth rate of perturbations with respect to the usual ΛCDM cosmology. Such results point to the possibility of a crucial observational test confronting CCDM with ΛCDM scenarios through a more detailed analysis involving CMB, weak lensing, as well as the large-scale structure.
Testing ΛCDM cosmology at turnaround: where to look for violations of the bound?
Tanoglidis, D.; Pavlidou, V.; Tomaras, T. N.
2015-12-01
In ΛCDM cosmology, structure formation is halted shortly after dark energy dominates the mass/energy budget of the Universe. A manifestation of this effect is that in such a cosmology the turnaround radius—the non-expanding mass shell furthest away from the center of a structure— has an upper bound. Recently, a new, local, test for the existence of dark energy in the form of a cosmological constant was proposed based on this turnaround bound. Before designing an experiment that, through high-precision determination of masses and —independently— turnaround radii, will challenge ΛCDM cosmology, we have to answer two important questions: first, when turnaround-scale structures are predicted to be close enough to their maximum size, so that a possible violation of the bound may be observable. Second, which is the best mass scale to target for possible violations of the bound. These are the questions we address in the present work. Using the Press-Schechter formalism, we find that turnaround structures have in practice already stopped forming, and consequently, the turnaround radius of structures must be very close to the maximum value today. We also find that the mass scale of ~ 1013 Msolar characterizes the turnaround structures that start to form in a statistically important number density today —and even at an infinite time in the future, since structure formation has almost stopped. This mass scale also separates turnaround structures with qualitatively different cosmological evolution: smaller structures are no longer readjusting their mass distribution inside the turnaround scale, they asymptotically approach their ultimate abundance from higher values, and they are common enough to have, at some epoch, experienced major mergers with structures of comparable mass; larger structures exhibit the opposite behavior. We call this mass scale the transitional mass scale and we argue that it is the optimal for the purpose outlined above. As a corollary, we
Statistics of the end of turnaround-scale structure formation in Lambda CDM cosmology
Tanoglidis, Dimitrios; Tomaras, Theodore
2014-01-01
In $\\Lambda$CDM cosmology, structure formation is halted shortly after dark energy dominates the mass/energy budget of the Universe. A manifestation of this effect is that in such a cosmology the turnaround radius --the non-expanding mass shell furthest away from the center of a structure-- has an upper bound. Recently, a new, local, test for the existence of dark energy in the form of a cosmological constant was proposed based on this turnaround bound. In this work, we build upon this proposal, and we further examine the advantages of studying the end of structure formation at the turnaround scale. Using the Press-Schechter formalism, we calculate the mass function of turnaround structures at various cosmic epochs, including the present one and an infinite time into the future. We find that structures at turnaround scales have in practice stopped forming already today, and consequently, the turnaround radii of structures must be very close to the maximum predicted value. We find that a mass scale of $m \\sim ...
Formation of Milky Way-type stellar haloes in a Λ-CDM cosmology
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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.
Is the continuous matter creation cosmology an alternative to $\\Lambda$CDM?
Fabris, J C; Piattella, O F
2014-01-01
The matter creation cosmology is revisited, including the evolution of baryons and dark matter particles. The creation process affects only dark matter and not baryons. The dynamics of the $\\Lambda$CDM model can be reproduced only if two conditions are satisfied: 1) the entropy density production rate and the particle density variation rate are equal and 2) the (negative) pressure associated to the creation process is constant. However, the matter creation model predicts a present dark matter-to-baryon ratio much larger than that observed in massive X-ray clusters of galaxies, representing a potential difficulty for the model. In the linear regime, a fully relativistic treatment indicates that baryons are not affected by the creation process but this is not the case for dark matter. Both components evolve together at early phases but lately the dark matter density contrast decreases since the background tends to a constant value. This behaviour produces a negative growth factor, in disagreement with observati...
Is the continuous matter creation cosmology an alternative to ΛCDM?
Energy Technology Data Exchange (ETDEWEB)
Fabris, J.C.; Pacheco, J.A. de Freitas; Piattella, O.F., E-mail: fabris@pq.cnpq.br, E-mail: pacheco@oca.eu, E-mail: oliver.piattella@pq.cnpq.br [Departamento de Física, Universidade Federal do Espírito Santo, Vitória, ES (Brazil)
2014-06-01
The matter creation cosmology is revisited, including the evolution of baryons and dark matter particles. The creation process affects only dark matter and not baryons. The dynamics of the ΛCDM model can be reproduced only if two conditions are satisfied: 1) the entropy density production rate and the particle density variation rate are equal and 2) the (negative) pressure associated to the creation process is constant. However, the matter creation model predicts a present dark matter-to-baryon ratio much larger than that observed in massive X-ray clusters of galaxies, representing a potential difficulty for the model. In the linear regime, a fully relativistic treatment indicates that baryons are not affected by the creation process but this is not the case for dark matter. Both components evolve together at early phases but lately the dark matter density contrast decreases since the background tends to a constant value. This behaviour produces a negative growth factor, in disagreement with observations, being a further problem for this cosmology.
Is the continuous matter creation cosmology an alternative to ΛCDM?
International Nuclear Information System (INIS)
The matter creation cosmology is revisited, including the evolution of baryons and dark matter particles. The creation process affects only dark matter and not baryons. The dynamics of the ΛCDM model can be reproduced only if two conditions are satisfied: 1) the entropy density production rate and the particle density variation rate are equal and 2) the (negative) pressure associated to the creation process is constant. However, the matter creation model predicts a present dark matter-to-baryon ratio much larger than that observed in massive X-ray clusters of galaxies, representing a potential difficulty for the model. In the linear regime, a fully relativistic treatment indicates that baryons are not affected by the creation process but this is not the case for dark matter. Both components evolve together at early phases but lately the dark matter density contrast decreases since the background tends to a constant value. This behaviour produces a negative growth factor, in disagreement with observations, being a further problem for this cosmology
Particle Accelerators Test Cosmological Theory.
Schramm, David N.; Steigman, Gary
1988-01-01
Discusses the symbiotic relationship of cosmology and elementary-particle physics. Presents a brief overview of particle physics. Explains how cosmological considerations set limits on the number of types of elementary particles. (RT)
Modified gravity: walk through accelerating cosmology
Bamba, Kazuharu; Odintsov, Sergei D
2013-01-01
We review the accelerating (mainly, dark energy) cosmologies in modified gravity. Special attention is paid to cosmologies leading to finite-time future singularities in $F(R)$, $F(G)$ and $\\mathcal{F}(R,G)$ modified gravities. The removal of the finite-time future singularities via addition of $R^2$-term which simultaneously unifies the early-time inflation with late-time acceleration is also briefly mentioned. Accelerating cosmology including the scenario unifying inflation with dark energy is considered in $F(R)$ gravity with Lagrange multipliers. In addition, we examine domain wall solutions in $F(R)$ gravity. Furthermore, covariant higher derivative gravity with scalar projectors is explored.
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...
Learn-as-you-go acceleration of cosmological parameter estimates
Aslanyan, Grigor; Easther, Richard; Price, Layne C.
2015-09-01
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 ΛCDM posterior probabilities. The computation is significantly accelerated without a pre-defined training set and uncertainties in the posterior probabilities are subdominant to statistical fluctuations. We have obtained a speedup factor of 6.5 for Metropolis-Hastings and 3.5 for nested sampling. Finally, we discuss the general requirements for a credible error model and show how to update them on-the-fly.
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.
Conformal symmetries of FRW accelerating cosmologies
International Nuclear Information System (INIS)
We show that any accelerating Friedmann–Robertson–Walker (FRW) cosmology with equation of state w<−1/3 (and therefore not only a de Sitter stage with w=−1) exhibits three-dimensional conformal symmetry on future constant-time hypersurfaces if the bulk theory is invariant under bulk conformal Killing vectors. We also offer an alternative derivation of this result in terms of conformal Killing vectors and show that long wavelength comoving curvature perturbations of the perturbed FRW metric are just conformal Killing motions of the FRW background. We then extend the boundary conformal symmetry to the bulk for accelerating cosmologies. Our findings indicate that one can easily generate perturbations of scalar fields which are not only scale invariant, but also fully conformally invariant on super-Hubble scales. Measuring a scale-invariant power spectrum for the cosmological perturbation does not automatically imply that the universe went through a de Sitter stage
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}_{\
Sp-brane accelerating cosmologies
International Nuclear Information System (INIS)
We investigate time dependent solutions (S-brane solutions) for product manifolds consisting of factor spaces where only one of them is non-Ricci-flat. Our model contains a minimally coupled free scalar field as a matter source. We discuss a possibility of generating late-time acceleration of the Universe. The analysis is performed in conformally related Brans-Dicke and Einstein frames. Dynamical behavior of our Universe is described by its scale factor. Since the scale factors of our Universe are described by different variables in both frames, they can have different dynamics. Indeed, we show that with our S-brane ansatz in the Brans-Dicke frame the stages of accelerating expansion exist for all types of the external space (flat, spherical, and hyperbolic). However, applying the same ansatz for the metric in the Einstein frame, we find that a model with flat external space and hyperbolic compactification of the internal space is the only one with the stage of the accelerating expansion. A scalar field can prevent this acceleration. It is shown that the case of hyperbolic external space in the Brans-Dicke frame is the only model which can satisfy experimental bounds for the fine-structure constant variations. We obtain a class of models where a pair of dynamical internal spaces have fixed total volume. This results in a fixed fine-structure constant. However, these models are unstable and external space is nonaccelerating
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
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...
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...
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
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.
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.
Little Rip, ΛCDM and singular dark energy cosmology from Born–Infeld- $f(R)$ gravity
Makarenko, Andrey N.; Sergei D. Odintsov; Olmo, Gonzalo J.
2014-01-01
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 ...
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...
Conformal symmetry and accelerating cosmology in teleparallel gravity
Bamba, Kazuharu; Odintsov, Sergei D.; Sáez-Gómez, Diego(Astrophysics, Cosmology and Gravity Centre (ACGC) and Department of Mathematics and Applied Mathematics, University of Cape Town, Rondebosch 7701, Cape Town, South Africa)
2013-01-01
We discuss conformal issues of pure and extended teleparallel gravity. In particular, we present formulations of conformal transformation in teleparallel gravity. Furthermore, we propose conformal scalar and gauge field theories in teleparallel gravity and study conformal torsion gravity. We explicitly demonstrate that a power-law acceleration (including the $\\Lambda$CDM universe) as well as the de Sitter expansion of the universe can be realized in extended teleparallel gravity with a confor...
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}ȯ 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}ȯ . 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}ȯ 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.
Binned Hubble parameter measurements and the cosmological deceleration–acceleration transition
International Nuclear Information System (INIS)
Weighted mean and median statistics techniques are used to combine 23 independent lower redshift, zda=0.74±0.05[30], which is expected in cosmological models with present-epoch energy budget dominated by dark energy as in the standard spatially-flat ΛCDM cosmological model
A class of transient acceleration models consistent with Big Bang cosmology
International Nuclear Information System (INIS)
Is it possible that the current cosmic accelerating expansion will turn into a decelerating one? Can this transition be realized by some viable theoretical model that is consistent with the standard Big Bang cosmology? We study a class of phenomenological models with a transient acceleration, based on a dynamical dark energy with a very general form of equation of state pde = βρde − βρdem. It mimics the cosmological constant ρde → const for a small scale factor a, and behaves as a barotropic gas with ρde → a−3(α+1) with α ≥ 0 for large a. The cosmic evolution of four models in the class has been examined in detail, and all yield a smooth transient acceleration. Depending on the specific model, the future universe may be dominated by either dark energy or by matter. In two models, the dynamical dark energy can be explicitly realized by a scalar field with an analytical potential V(φ). Moreover, a statistical analysis shows that the models can be as robust as ΛCDM in confronting the observational data of Type Ia supernovae, cosmic microwave background (CMB) and baryon acoustic oscillation. As improvements over previous studies, our models overcome the problem of over-abundance of dark energy during early eras, and satisfy the constraints on dark energy from WMAP observations of CMB
Velocity, Acceleration and Cosmic Distances in Cosmological Special Relativity
Carmeli, Moshe
2001-01-01
In this paper we present the fundamentals of the cosmological special relativity (CSR) by discussing the dynamical concepts of velocity, acceleration and cosmic distances in spacevelocity. These concepts occur in CSR just as those of mass, linear momentum and energy appear in Einstein's special relativity (ESR) in spacetime.
Another coincidence problem for $\\Lambda$CDM?
van Oirschot, Pim; Lewis, Geraint F
2014-01-01
Over the last nine years of cosmic microwave background observations, the Wilkinson Microwave Anisotropy Probe ($WMAP$) results were consistent with a $\\Lambda$CDM cosmological model in which the age of the Universe is one Hubble time, and the time-averaged value of the deceleration parameter is consistent with zero. This curious observation has been put forward as a new coincidence problem for the $\\Lambda$CDM concordance cosmology, which is in fact a `greater' coincidence than the near equality of the density parameters of matter and the cosmological constant. At the moment of writing these conference proceedings, the Planck Collaboration has released its first cosmological data, which revealed a small shift in the $\\Lambda$CDM cosmological parameters when compared to $WMAP$. We show that under the assumption of a spatially flat $\\Lambda$CDM cosmology, Planck's results remove this coincidence problem for $\\Lambda$CDM at greater than 99\\% confidence level.
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.
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.
Future cosmological surveys and the cosmic deceleration/acceleration transition
International Nuclear Information System (INIS)
Full text: Since the discovery of the accelerated expansion of the universe in 1998, considerable effort in cosmology has been devoted to determine the source of this acceleration. The two most common possibilities discussed in the literature are: the existence of an exotic component with sufficiently negative pressure (dark energy) and proper modifications of general relativity at cosmological scales. One way of making progress in determining the cosmic expansion history is through a model by model analysis. Another is to carry out a phenomenological analysis with the use of different parameterizations of the dark energy equation of state, the Hubble parameter or the dark energy density. This procedure may provide interesting pieces of information, but in general a parametrization assumes the existence of dark matter and dark energy and general relativity is in most cases assumed. In this framework, an important question regards the number of parameters necessary to get reliable conclusions. In this framework, a important question regards the number of parameters necessary to get reliable conclusions. In this work we are mainly interested in the following questions: what is the redshift of the transition from decelerated to accelerated expansion? How fast was it? We investigate these by introducing a new parameterization for the deceleration parameter (q) that depends on four parameters: the initial value and final values of q, the redshift of the transition and a quantity related to the width in redshift of such transition. With this formulation we aim to answer the above questions with the minimum amount of assumptions about the dark sector and the fundamental gravitation theory. This kind of parameterization is very interesting because generalize many cosmological models. We investigated, trough simulations, the imposed observational constraints under the class of models mentioned, by future Supernova type Ia (SNIa) surveys, Baryon Acoustic Oscillations (BAO
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...
Rotating and accelerating black holes with cosmological constant
Chen, Yu; 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 arise from it.
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.
Caching and interpolated likelihoods: accelerating cosmological Monte Carlo Markov chains
International Nuclear Information System (INIS)
We describe a novel approach to accelerating Monte Carlo Markov Chains. Our focus is cosmological parameter estimation, but the algorithm is applicable to any problem for which the likelihood surface is a smooth function of the free parameters and computationally expensive to evaluate. We generate a high-order interpolating polynomial for the log-likelihood using the first points gathered by the Markov chains as a training set. This polynomial then accurately computes the majority of the likelihoods needed in the latter parts of the chains. We implement a simple version of this algorithm as a patch (InterpMC) to CosmoMC and show that it accelerates parameter estimatation by a factor of between two and four for well-converged chains. The current code is primarily intended as a ''proof of concept'', and we argue that there is considerable room for further performance gains. Unlike other approaches to accelerating parameter fits, we make no use of precomputed training sets or special choices of variables, and InterpMC is almost entirely transparent to the user
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.
International Nuclear Information System (INIS)
The newly released observational H(z) data (OHD) is used to constrain Λ(t)CDM models as holographic and agegraphic dark energy. By the use of the length scale and time scale as the IR cut-off including Hubble horizon (HH), future event horizon (FEH), age of the universe (AU), and conformal time (CT), we achieve four different Λ(t)CDM models which can describe the present cosmological acceleration respectively. In order to get a comparison between such Λ(t)CDM models and standard ΛCDM model, we use the information criteria (IC), Om(z) diagnostic, and statefinder diagnostic to measure the deviations. Furthermore, by simulating a larger Hubble parameter data sample in the redshift range of 0.1 < z < 2.0, we get the improved constraints and more sufficient comparison. We show that OHD is not only able to play almost the same role in constraining cosmological parameters as SNe Ia does but also provides the effective measurement of the deviation of the DE models from standard ΛCDM model. In the holographic and agegraphic scenarios, the results indicate that the FEH is more preferable than HH scenario. However, both two time scenarios show better approximations to ΛCDM model than the length scenarios
Miniati, Francesco; Ryu, Dongsu; Kang, Hyesung; Jones, T. W.
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...
Accelerating cosmology in modified gravity with scalar field
Shaido, Yulia A.; Sugamoto, Akio
2004-01-01
The modified gravity with 1/R term (R being scalar curvature) and the Einstein-Hilbert term is studied by incorporating the phantom scalar field. A number of cosmological solutions are derived in the presence of the phantom field in the perfect fluid background. It is shown the current inflation obtained in the modified gravity is affected by the existence the phantom field.
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...
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...
Aledo, Juan A.; Rubio, Rafael M.
2016-06-01
We study the scalar curvature of spacelike hypersurfaces in the family of cosmological models known as generalized Robertson-Walker spacetimes, and give several rigidity results under appropriate mathematical and physical assumptions. On the other hand, we show that this family of spacetimes provides suitable models obeying the null convergence condition to explain accelerated expanding universes.
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.
de Cesare, Marco; Sakellariadou, Mairi
2016-01-01
We study the cosmological implications of interactions between spacetime quanta in the Group Field Theory (GFT) approach to Quantum Gravity from a phenomenological perspective. Our work represents a first step towards understanding Early Universe Cosmology by studying the dynamics of the emergent continuum spacetime, as obtained from a fundamentally discrete microscopic theory. In particular, we show how GFT interactions lead to a recollapse of the Universe while preserving the bounce replacing the initial singularity, which has already been shown to occur in the free case. It is remarkable that cyclic cosmologies are thus obtained in this framework without any a priori assumption on the geometry of spatial sections of the emergent spacetime. Furthermore, we show how interactions make it possible to have an early epoch of accelerated expansion, which can be made to last for an arbitrarily large number of e-folds, without the need to introduce an ad hoc potential for the scalar field.
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.
Fermions as sources of accelerated regimes in cosmology
International Nuclear Information System (INIS)
In this work it is investigated if fermionic sources could be responsible for accelerated periods during the evolution of a universe where a matter field would answer for the decelerated period. The self-interaction potential of the fermionic field is considered as a function of the scalar and pseudoscalar invariants. Irreversible processes of energy transfer between the matter and gravitational fields are also considered. It is shown that the fermionic field could behave like an inflaton field in the early universe and as dark energy for an old universe
The possibility of an accelerating cosmology in Rastall's theory
International Nuclear Information System (INIS)
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. Tμv;μ ≠ 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 ΩM ≅ 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.
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.)
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 India
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 China
CDM Country Guide for Indonesia
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 Indonesia
CDM Country Guide for Thailand
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 Thailand
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
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...
Lieu, Richard
2007-01-01
Astronomy can never be a hard core physics discipline, because the Universe offers no control experiment, i.e. with no independent checks it is bound to be highly ambiguous and degenerate. Thus e.g. while superluminal motion can be explained by Special Relativity. data on the former can never on their own be used to establish the latter. This is why traditionally astrophysicists have been content with (and proud of) their ability to use known physical laws and processes established in the laboratory to explain celestial phenomena. Cosmology is not even astrophysics: all the principal assumptions in this field are unverified (or unverifiable) in the laboratory, and researchers are quite comfortable with inventing unknowns to explain the unknown. How then could, after fifty years of failed attempt in finding dark matter, the fields of dark matter {\\it and now} dark energy have become such lofty priorities in astronomy funding, to the detriment of all other branches of astronomy? I demonstrate in this article th...
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
Tartaglia, Angelo
2016-01-01
Starting from some relevant facts concerning the behavior of the universe over large scale and time span, the analogy between the geometric approach of General Relativity 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 reproduces 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 theories. The possible role of structure topological defects is also mentioned. The conclusion is that SSC is at least as good as the ΛCDM standard cosmology, giving a more intuitive interpretation of the physical nature of the phenomena.
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)
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.
The Turning Point for the Recent Acceleration of the Universe with a Cosmological Constant
Directory of Open Access Journals (Sweden)
Zhang T. X.
2012-04-01
Full Text Available The turning point and acceleration expansion of the universe are investigated according to the standard cosmological theory with a non-zero cosmological constant. Choosing the Hubble constant H 0 , the radius of the present universe R 0 , and the density parameter in matter Ω M , 0 as three independent parameters, we have analytically examined the other properties of the universe such as the density parameter in dark energy, the cosmologi- cal constant, the mass of the universe, the turning point redshift, the age of the present universe, and the time-dependent radius, expansion rate, velocity, and acceleration pa- rameter of the universe. It is shown that the turning point redshift is only dependent of the density parameter in matter, not explicitly on the Hubble constant and the radius of the present universe. The universe turned its expansion from past deceleration to recent acceleration at the moment when its size was about 3 / 5 of the present size if the density parameter in matter is about 0.3 (or the turning point redshift is 0.67. The expansion rate is very large in the early period and decreases with time to approach the Hubble constant at the present time. The expansion velocity exceeds the light speed in the early period. It decreases to the minimum at the turning point and then increases with time. The minimum and present expansion velocities are determined with the independent parameters. The solution of time-dependent radius shows the universe expands all the time. The universe with a larger present radius, smaller Hubble constant, and / or smaller density parameter in matter is elder. The universe with smaller density parameter in matter accelerates recently in a larger rate but less than unity.
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.
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
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
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.
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 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
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 Λ 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.
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.
Maps of CMB lensing deflection from N-body simulations in Coupled Dark Energy Cosmologies
International Nuclear Information System (INIS)
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 σ8, 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 contrast and of the matter abundance lead to a
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...
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...
Late time acceleration in a non-commutative model of modified cosmology
Directory of Open Access Journals (Sweden)
B. Malekolkalami
2014-12-01
Full Text Available 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.
Super-accelerating bouncing cosmology in asymptotically free non-local gravity
Energy Technology Data Exchange (ETDEWEB)
Calcagni, Gianluca [CSIC, Instituto de Estructura de la Materia, Madrid (Spain); Modesto, Leonardo [Fudan University, Department of Physics and Center for Field Theory and Particle Physics, Shanghai (China); Nicolini, Piero [Johann Wolfgang Goethe-Universitaet, Frankfurt Institute for Advanced Studies (FIAS) und Institut fuer Theoretische Physik, Frankfurt am Main (Germany)
2014-08-15
Recently, evidence has been collected that a class of gravitational theories with certain non-local operators is renormalizable. We consider one such model which, at the linear perturbative level, reproduces the effective non-local action for the light modes of bosonic closed string-field theory. Using the property of asymptotic freedom in the ultraviolet and fixing the classical behavior of the scale factor at late times, an algorithm is proposed to find general homogeneous cosmological solutions valid both at early and late times. Imposing a power-law classical limit, these solutions (including anisotropic ones) display a bounce, instead of a big-bang singularity, and super-accelerate near the bounce even in the absence of an inflaton or phantom field. (orig.)
Cosmological perturbations of self-accelerating universe in nonlinear massive gravity
International Nuclear Information System (INIS)
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 modification of stochastic gravitational wave spectrum
Late time acceleration in a non-commutative model of modified cosmology
International Nuclear Information System (INIS)
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
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.
Gravitational vacuum energy in our recently accelerating universe
Bludman, Sidney
2008-01-01
We review current observations of the homogeneous cosmological expansion which, because they measure only kinematic variables, cannot determine the dynamics driving the recent accelerated expansion. The minimal fit to the data, the flat $\\Lambda CDM$ model, consisting of cold dark matter and a cosmological constant, interprets $4\\Lambda$ geometrically as a classical spacetime curvature constant of nature, avoiding any reference to quantum vacuum energy. (The observed Uehling and Casimir effects measure forces due to QED vacuum polarization, but not any quantum material vacuum energies.) An Extended Anthropic Principle, that Dark Energy and Dark Gravity be indistinguishable, selects out flat $\\Lambda CDM$. Prospective cosmic shear and galaxy clustering observations of the growth of fluctuations are intended to test whether the 'dark energy' driving the recent cosmological acceleration is static or moderately dynamic. Even if dynamic, observational differences between an additional negative-pressure material co...
Barbosa, C M S; Piattella, O F; Velten, H E S; Zimdahl, W
2015-01-01
We discuss the possibility to implement a viscous cosmological model, attributing to the dark matter component a behaviour described by bulk viscosity. Since bulk viscosity implies negative pressure, this rises the possibility to unify the dark sector. At the same time, the presence of dissipative effects may alleviate the so called small scale problems in the $\\Lambda$CDM model. While the unified viscous description for the dark sector does not lead to consistent results, the non-linear behaviour indeed improves the situation with respect to the standard cosmological model.
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.
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.
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.
Future design of CDM; Framtida utformning av CDM
Energy Technology Data Exchange (ETDEWEB)
Evander, Anna
2004-01-01
The Kyoto Protocol was adopted in 1997 as a way to combat greenhouse gas emissions and climate change. The Kyoto Protocol contains three flexible mechanisms that will help the parties achieve their emission targets cost effectively. One of the flexible mechanisms - the Clean Development Mechanism (CDM) - is further investigated and evaluated in this essay. Through the CDM the developed countries perform and invest in greenhouse gas reducing projects in developing countries. The investing country will get credits for the achieved emission reductions while the host country will benefit from technology transfer and sustainable development. CDM is supervised by the CDM Executive Board. Rules and procedures of the CDM are developed by CDM Executive Board in parallel with the first project applications. Other tasks of the CDM Executive Board are to approve new methodologies related to baselines and monitoring plans, and to develop and maintain a registry over CDM projects and their issued emission reductions. Two multilateral funds that have come far in establishing CDM projects are the World Bank Prototype Carbon Fund (PCF) and the Dutch fund CERUPT. The technical and geographical distribution of the projects is uneven. Most of the projects in these funds concern renewable energy and very few concern energy efficiency, though the PCF strive for more energy efficiency projects. The majority of the projects are conducted in Latin America and, in the case of CERUPT, not a single project is conducted in Africa. Some difficulties have occurred in the implementation of CDM projects. Those concerned in this essay are additionally, transaction costs, sustainable development, technology transfer and small scale projects. When implementing a CDM project you have to show that the project is additional, that is that it would not have occurred in the absence of CDM. Transaction costs are the costs derived from applying, reporting, monitoring and registering of a project. The
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...
Odintsov, S. D.; Oikonomou, V. K.
2016-06-01
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 era follows, which lasts until the second Type IV singularity, and then the late-time acceleration era follows. The models have two appealing features: firstly they produce a nearly scale invariant power spectrum of primordial curvature perturbations and a scalar-to-tensor ratio which are compatible with the most recent observational data and secondly, it seems that the deceleration–acceleration transition is crucially affected by the presence of the second Type IV singularity which occurs at the end of the matter domination era. As we demonstrate, the Hubble horizon at early times shrinks, as expected for an initially accelerating Universe, then during the matter domination era, it expands and finally after the Type IV singularity, the Hubble horizon starts to shrink again, during the late-time acceleration era. Intriguingly enough, the deceleration–acceleration transition, occurs after the second Type IV singularity. In addition, we investigate which F
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.
Inflation and late-time acceleration from a double-well potential with cosmological constant
de Haro, Jaume
2016-01-01
A model of a universe without big bang singularity is presented, which displaysanearly inflationary period ending just before a phase transition to a deflationary 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 $\\Lambda$CDM scenario.
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
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.
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
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)
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, ...
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
Is cosmography a useful tool for testing cosmology?
Busti, Vinicius C; de la Cruz-Dombriz, Alvaro; Saez-Gomez, Diego
2015-01-01
Model-independent methods in cosmology have become an essential tool in order to deal with an increasing number of theoretical alternatives for explaining the late-time acceleration of the Universe. In principle, this provides a way of testing the Cosmological Concordance (or $\\Lambda$CDM) model under different assumptions and to rule out whole classes of competing theories. One such model-independent method is the so-called cosmographic approach, which relies only in the homogeneity and isotropy of the Universe on large scales. We show that this method suffers from many shortcomings, providing biased results depending on the auxiliary variable used in the series expansion and is unable to rule out models or adequately reconstruct theories with higher-order derivatives in either the gravitational or matter sector. Consequently, in its present form, this method seems unable to provide reliable or useful results for cosmological applications.
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.
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...
A tilted cold dark matter cosmological scenario
Cen, Renyue; Gnedin, Nickolay Y.; Kofman, Lev A.; Ostriker, Jeremiah P.
1992-01-01
A new cosmological scenario based on CDM but with a power spectrum index of about 0.7-0.8 is suggested. This model is predicted by various inflationary models with no fine tuning. This tilted CDM model, if normalized to COBE, alleviates many problems of the standard CDM model related to both small-scale and large-scale power. A physical bias of galaxies over dark matter of about two is required to fit spatial observations.
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...
Odintsov, S. D.; Oikonomou, V. K.
2016-01-01
We study mimetic F (R ) gravity with a potential and Lagrange multiplier constraint. In the context of these theories, we introduce a reconstruction technique which enables us to realize arbitrary cosmologies, given the Hubble rate and an arbitrarily chosen F (R ) gravity. We exemplify our method by realizing cosmologies that are in concordance with current observations (Planck data) and also well-known bouncing cosmologies. The attribute of our method is that the F (R ) gravity can be arbitrarily chosen, so we can have the appealing features of the mimetic approach combined with the known features of some F (R ) gravities, which unify early-time with late-time acceleration. Moreover, we study the existence and the stability of de Sitter points in the context of mimetic F (R ) gravity. In the case of unstable de Sitter points, it is demonstrated that graceful exit from inflation occurs. We also study the Einstein-frame counterpart theory of the Jordan-frame mimetic F (R ) gravity, and we discuss the general properties of the theory and exemplify our analysis by studying a quite interesting (from a phenomenological point of view) model with two scalar fields. We also calculate the observational indices of the two-scalar-field model, by using the two-scalar-field formalism. Furthermore, we extensively study the dynamical system that corresponds to the mimetic F (R ) gravity, by finding the fixed points and studying their stability. Finally, we modify our reconstruction method to function in the inverse way and thus yield which F (R ) gravity can realize a specific cosmological evolution, given the mimetic potential and the Lagrange multiplier.
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...
Yang, Qiaoli
I started work on the field of dark matter and cosmology with Dr. Sikivie three years ago with a goal to distinguish observationally axions or axion-like particles (ALPs) from other dark matter candidates such as weakly interacting massive particles (WIMPs) and sterile neutrinos. The subject is exciting because if one can determine the identity of the dark matter, it will be a mile-stone of physics beyond the standard model. On the high energy frontier, the standard model with three generation fermions is firmly established. However, it is not complete because the theory does not contain a plausible dark matter candidate, with properties required from observation, and the theory has fine-tuning problems such as the strong CP problem. On the cosmology and astrophysics frontiers, new observations of the dynamics of galaxy clusters, the rotation curves of galaxies, the abundances of light elements, gravitational lensing, and the anisotropies of the CMBR reach unprecedented accuracy. They imply cold dark matter (CDM) is 23% of the total energy density of the universe. Although many "beyond the standard model" theories may provide proper candidates to serve as CDM particles, the axion is especially compelling because it not only serves as the CDM particle, but also solves the strong CP problem. The axion was initially motivated by the strong CP problem, namely the puzzle why there is no CP violation in the strong interactions. Peccei and Quinn solved the problem by introducing a new UPQ(1) symmetry, and later Weinberg and Wilczek pointed out that the spontaneous breaking of UPQ(1) symmetry leads to a new pseudoscalar particle, the axion[1][2][3]. Axion models were proposed in which the symmetry breaking scale may be much larger than the electroweak scale, in which case the axion is very light and couples extremely weakly to ordinary matter. Furthermore, it was realized [4] that the cold axions, produced by the misalignment mechanism during the QCD phase transition, have
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...
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...
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.
Analytical Study on the Cosmological Large-scale Structure in an Accelerating Universe
Wang, Xin
2012-01-01
Motivated by the roughly log-normal probability density distribution function (PDF) of the small scale density field, we develop cosmological perturbation theory for the power spectrum of a logarithmically transformed density field with the formalism which is developed in the context of the cosmological renormalized perturbation theory. Compared with the standard perturbation theory, our approach help to regulate the convergence behavior of the perturbation series, and of the Taylor series expansion we use for the logarithmic mapping. The perturbation calculation achieved good agreement with simulation results. Then we consider the topology of the iso-density contour of the density field, especially the genus. The genus is relatively insensitive to nonlinear gravitational evolution, clustering bias and redshift distortion, and is approximately conserved over time as structures grow in Einstein's general relativity, hence it can be used as a robust standard ruler for cosmological measurements. However, in modified gravity models where structures grow with different rates on different scales, the genus should change over time, and therefore it can be used to test the gravity models on large scales. We studied the case of the f(R) theory, DGP brane-world theory as well as phenomenological models. We also forecast how the modified gravity models can be constrained with optical/IR or 21cm surveys in the near future.
A Test of Cosmological Models Using High-z Measurements of H(z)
Melia, Fulvio; McClintock, Thomas M.
2015-10-01
The recently constructed Hubble diagram using a combined sample of SNLS and SDSS-II SNe Ia, and an application of the Alcock-Paczyński (AP) test using model-independent Baryon Acoustic Oscillation (BAO) data, have suggested that the principal constraint underlying the cosmic expansion is the total equation-of-state of the cosmic fluid, rather than that of its dark energy. These studies have focused on the critical redshift range (0 ≲ z ≲ 2) within which the transition from decelerated to accelerated expansion is thought to have occurred, and they suggest that the cosmic fluid has zero active mass, consistent with a constant expansion rate. The evident impact of this conclusion on cosmological theory calls for an independent confirmation. In this paper, we carry out this crucial one-on-one comparison between the Rh = ct universe (a Friedmann-Robertson-Walker cosmology with zero active mass) and wCDM/ΛCDM, using the latest high-z measurements of H(z). Whereas the SNe Ia yield the integrated luminosity distance, while the AP diagnostic tests the geometry of the universe, the Hubble parameter directly samples the expansion rate itself. We find that the model-independent cosmic chronometer data prefer Rh = ct over wCDM/ΛCDM with a Bayes Information Criterion likelihood of ˜95% versus only ˜5%, in strong support of the earlier SNe Ia and AP results. This contrasts with a recent analysis of H(z) data based solely on BAO measurements which, however, strongly depend on the assumed cosmology. We discuss why the latter approach is inappropriate for model comparisons, and emphasize again the need for truly model-independent observations to be used in cosmological tests.
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
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, ...
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}\
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...
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.
International Nuclear Information System (INIS)
Several different explicit reconstructions of f(R) gravity are obtained from the background Friedmann-Laimatre-Robertson-Walker expansion history. It is shown that the only theory whose Lagrangian is a simple function of the Ricci scalar R, that admits an exact ΛCDM expansion history, is standard general relativity with a positive cosmological constant and the only way to obtain this behavior of the scale factor for more general functions of R is to add additional degrees of freedom to the matter sector.
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.
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.
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.
Continuous matter creation and the acceleration of the universe: a replay
de Roany, Alain
2010-01-01
In a recent note (arXiv:1012.5069), the investigation performed by the present authors on the evolution of density fluctuations in an accelerated universe including matter creation was criticized. The criticism is based on the fact that the Newtonian background is not "accelerating", invalidating the conclusions of the linear analysis. We show that our linear equations describe adequately an accelerating universe in which the pressure associated to the creation process is constant, a model equivalent to the $\\Lambda$CDM cosmology. Thus, our previous conclusions remain unchanged.
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...
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...
Cosmological models and gravitational lenses
International Nuclear Information System (INIS)
Full text: The large amount of observational data collected since the early last century by Surveys as: CLASS, SNAP, SDSS and others, made the tests possible cosmological models. What stands out most is one that uses gravitational lensing, which serves as a complement to tests with SNe-Ia. Currently, the observations indicate that the universe is accelerated expansion. Moreover to that we have the cosmic structures we observe today as the need to add more material. A proposal usual to solve these problems is to propose the existence of two dark components. This name comes from the constituents emitted any radiation. However, despite both not emit radiation they must distort space-time somehow. Thus, when a beam of light from any source in this region spreads geometrically modified, will have its trajectory changed. Therefore, the phenomenon of gravitational lensing allows infer indirectly the amount of dark matter in the universe. Moreover, the study of gravitational lensing enables to obtain cosmological parameters as the Hubble constant and density parameter. Moreover, this effect can heaven be used to detect exoplanets, or also as a natural telescope. In this study aims to assess some cosmological models using gravitational lenses and the CLASS data in tests with fluids quartessence. Such fluids are useful for treating the matter and dark energy as a single fluid. Unlike the model LambdaCDM that treats separately, i.e. in this model the universe consists of baryons, radiation, dust, dark matter and dark energy. We will use the statistics of gravitational lensing to make a comparison between the generalized Chaplygin gas and the viscous fluid. In addition, an application of statistics to the CLASS lenses will be applied in models well accepted by the scientific community. (author)
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.
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.
Which spectral distortions does ΛCDM actually predict?
Chluba, Jens
2016-04-01
Ever refined cosmological measurements have established the ΛCDM 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 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 modeling of foregrounds and instrumental aspects, as we briefly discuss here.
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.
Cosmological back-reaction in modified gravity and its implications for dark energy
International Nuclear Information System (INIS)
We study the effective stress-energy tensor induced by cosmological inhomogeneity in f(R)=R+c R2 and equivalent scalar-tensor theories, motivated both by models of early universe inflation and by phenomenological alternative cosmologies to the standard Λ-CDM. We use Green and Wald's framework for averaging over classical fluctuations of short-wavelength λ. By ensuring that the leading non-linear terms from the fluctuations of the Einstein terms and the corrections both contribute in the formal limit as λ→0, we derive a diffeomorphism invariant effective stress-energy tensor whose trace is non-vanishing and of the right sign to potentially account for the current acceleration of the universe. However a more phenomenologically acceptable dark energy model would be required if this effect were to fully account for the current acceleration
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.
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.
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.
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)
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 ...
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)
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.
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...
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
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.
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 ...
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...
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.
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.
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...
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 ...
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
International Nuclear Information System (INIS)
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 to 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 ΛCDM 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/dark-energy unification models. We also present a short discussion on the causal propagation in nonlinear scalar field theories such as the one proposed here
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...
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, $\
A dynamical system study of the inhomogeneous Λ-CDM model
International Nuclear Information System (INIS)
We consider spherically symmetric inhomogeneous dust models with a positive cosmological constant, Λ, given by the LemaItre-Tolman-Bondi metric. These configurations provide a simple but useful generalization of the Λ-CDM model describing cold dark matter (CDM) and a Λ term, which seems to fit current cosmological observations. The dynamics of these models can be fully described by scalar evolution equations that can be given in the form of a proper dynamical system associated with a four-dimensional phase space whose critical points and invariant subspaces are examined and classified. The phase space evolution of various configurations is studied in detail by means of two two-dimensional subspaces: a projection into the invariant homogeneous subspace associated with Λ-CDM solutions with FLRW metric, and a projection into a subspace generated by suitably defined fluctuations that convey the effects of inhomogeneity. We look at cases with perpetual expansion, bouncing and loitering behavior, as well as configurations with 'mixed' kinematic patters, such as a collapsing region in an expanding background. In all cases, phase space trajectories emerge from and converge to stable past and future attractors in a qualitatively analogous way as in the case of the FLRW limit. However, we can identify in both projections of the phase space various qualitative features absent in the FLRW limit that can be useful in the construction of toy models of astrophysical and cosmological inhomogeneities.
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.
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.
Minimal noncanonical cosmologies
International Nuclear Information System (INIS)
We demonstrate how much it is possible to deviate from the standard cosmological paradigm of inflation-assisted ΛCDM, keeping within current observational constraints, and without adding to or modifying any theoretical assumptions. We show that within a minimal framework there are many new possibilities, some of them wildly different from the standard picture. We present three illustrative examples of new models, described phenomenologically by a noncanonical scalar field coupled to radiation and matter. These models have interesting implications for inflation, quintessence, reheating, electroweak baryogenesis, and the relic densities of WIMPs and other exotics
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...
Cosmological dynamics of extended chameleons
Tamanini, Nicola; Wright, Matthew
2016-04-01
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 ΛCDM 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.
Bimetric gravity is cosmologically viable
Akrami, Yashar; Hassan, S. F.; Könnig, Frank; Schmidt-May, Angnis; Solomon, Adam R.
2015-09-01
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.
Bimetric gravity is cosmologically viable
Akrami, Yashar; Könnig, Frank; Schmidt-May, Angnis; Solomon, Adam R
2015-01-01
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, $M_f$, 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 $\\Lambda$CDM, but with a technically-natural value for the cosmological constant. We find $M_f$ should be no larger than the electroweak scale in order for cosmological perturbations to be stable by big-bang nucleosynthesis.
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.
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...
Energy Technology Data Exchange (ETDEWEB)
Chimento, L P; Forte, M [Physics Department, UBA, 1428 Buenos Aires (Argentina); Devecchi, F P; Kremer, G M; Ribas, M O; Samojeden, L L, E-mail: kremer@fisica.ufpr.br, E-mail: devecchi@fisica.ufpr.br, E-mail: chimento@df.uba.ar [Physics Department, UFPR, 81531-990 Curitiba (Brazil)
2011-07-08
In this work we review if fermionic sources could be responsible for accelerated periods during the evolution of a FRW universe. In a first attempt, besides the fermionic source, a matter constituent would answer for the decelerated periods. The coupled differential equations that emerge from the field equations are integrated numerically. The self-interaction potential of the fermionic field is considered as a function of the scalar and pseudo-scalar invariants. It is shown that the fermionic field could behave like an inflaton field in the early universe, giving place to a transition to a matter dominated (decelerated) period. In a second formulation we turn our attention to analytical results, specifically using the idea of form-invariance transformations. These transformations can be used for obtaining accelerated cosmologies starting with conventional cosmological models. Here we reconsider the scalar field case and extend the discussion to fermionic fields. Finally we investigate the role of a Dirac field in a Brans-Dicke (BD) context. The results show that this source, in combination with the BD scalar, promote a final eternal accelerated era, after a matter dominated period.
International Nuclear Information System (INIS)
In this work we review if fermionic sources could be responsible for accelerated periods during the evolution of a FRW universe. In a first attempt, besides the fermionic source, a matter constituent would answer for the decelerated periods. The coupled differential equations that emerge from the field equations are integrated numerically. The self-interaction potential of the fermionic field is considered as a function of the scalar and pseudo-scalar invariants. It is shown that the fermionic field could behave like an inflaton field in the early universe, giving place to a transition to a matter dominated (decelerated) period. In a second formulation we turn our attention to analytical results, specifically using the idea of form-invariance transformations. These transformations can be used for obtaining accelerated cosmologies starting with conventional cosmological models. Here we reconsider the scalar field case and extend the discussion to fermionic fields. Finally we investigate the role of a Dirac field in a Brans-Dicke (BD) context. The results show that this source, in combination with the BD scalar, promote a final eternal accelerated era, after a matter dominated period.
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.
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...
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...
Alcock-paczynski cosmological test
International Nuclear Information System (INIS)
In order to test the expansion of the universe and its geometry, we carry out an Alcock-Paczyński cosmological test, that is, an evaluation of the ratio of observed angular size to radial/redshift size. The main advantage of this test is that it does not depend on the evolution of the galaxies but only on the geometry of the universe. However, the redshift distortions produced by the peculiar velocities of the gravitational infall also have an influence, which should be separated from the cosmological effect. We derive the anisotropic correlation function of sources in three surveys within the Sloan Digital Sky Survey (SDSS): galaxies from SDSS-III/Baryon Oscillation Spectroscopic Survey Data Release 10 (BOSS-DR10) and QSOs from SDSS-II and SDSS-III/BOSS-DR10. From these, we are able to disentangle the dynamic and geometric distortions and thus derive the ratio of observed angular size to radial/redshift size at different redshifts. We also add some other values available in the literature. Then we use the data to evaluate which cosmological model fits them. We used six different models: concordance ΛCDM, Einstein-de Sitter, open-Friedman cosmology without dark energy, flat quasi-steady state cosmology, a static universe with a linear Hubble law, and a static universe with tired-light redshift. Only two of the six models above fit the data of the Alcock-Paczyński test: concordance ΛCDM and static universe with tired-light redshift, whereas the rest of them are excluded at a >95% confidence level. If we assume that ΛCDM is the correct one, the best fit with a free Ω m is produced for Ωm=0.24−0.07+0.10.
Direct measurement of the cosmic acceleration by 21cm absorption systems
Yu, Hao-Ran; Pen, Ue-Li
2013-01-01
So far there is only indirect evidence that the universe is undergoing an accelerated expansion. The evidence for cosmic acceleration is based on the observation of different objects at different distances, and requires invoking the Copernican cosmological principle, and Einstein's equations of motion. We examine the direct observability using recession velocity drifts (Sandage-Loeb effect) of 21cm hydrogen absorption systems in upcoming radio surveys. This measures the change in velocity of the {\\it same} objects separate by a time interval and is a model-independent measure of acceleration. We forecast that for a CHIME-like survey with a decade time span, we can detect the acceleration of a $\\Lambda$CDM universe with $\\sim 6\\sigma$ confidence. This acceleration test requires modest data analysis and storage changes from the normal processing, and cannot be recovered retroactively.
Viable Singularity-Free f(R) Gravity Without a Cosmological Constant
Miranda, Vinicius; Waga, Ioav; Quartin, Miguel
2009-01-01
Several authors have argued that self-consistent $f(R)$ gravity models distinct from $\\Lambda $CDM are almost ruled out. Confronting such claims, we present a particular two-parameter $f(R)$ model that: (a) is cosmologically viable and distinguishable from $\\Lambda $CDM; (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.
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...
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
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...
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.
Quantifying concordance in cosmology
Seehars, Sebastian; Grandis, Sebastian; Amara, Adam; Refregier, Alexandre
2016-05-01
Quantifying the concordance between different cosmological experiments is important for testing the validity of theoretical models and systematics in the observations. In earlier work, we thus proposed the Surprise, a concordance measure derived from the relative entropy between posterior distributions. We revisit the properties of the Surprise and describe how it provides a general, versatile, and robust measure for the agreement between data sets. We also compare it to other measures of concordance that have been proposed for cosmology. As an application, we extend our earlier analysis and use the Surprise to quantify the agreement between WMAP 9, Planck 13, and Planck 15 constraints on the Λ CDM model. Using a principle component analysis in parameter space, we find that the large Surprise between WMAP 9 and Planck 13 (S =17.6 bits, implying a deviation from consistency at 99.8% confidence) is due to a shift along a direction that is dominated by the amplitude of the power spectrum. The Planck 15 constraints deviate from the Planck 13 results (S =56.3 bits), primarily due to a shift in the same direction. The Surprise between WMAP and Planck consequently disappears when moving to Planck 15 (S =-5.1 bits). This means that, unlike Planck 13, Planck 15 is not in tension with WMAP 9. These results illustrate the advantages of the relative entropy and the Surprise for quantifying the disagreement between cosmological experiments and more generally as an information metric for cosmology.
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
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.
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.
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...
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.
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...
Selecting a CDM investor in China: A critical analysis
International Nuclear Information System (INIS)
The Kyoto Protocol adopted three flexible market-based mechanisms (Emissions Trading; Joint Implementation; Clean Development Mechanism) to meet emission reduction targets in a cost-effective manner. Of these, the Clean Development Mechanism (CDM) is the only mechanism that links developed and developing countries. China has been a dominant player in CDM markets with >50.86% of the world's 4768 CDM projects. This study surveyed key CDM stakeholders from which the identification and ranking of the 10 most important factors that determine the selection of CDM investors in China. The most important factors were “reputation of company” and “experience in CDM project in China” whilst “personal friendship or relationship” was the least influential. European countries (mainly UK, The Netherlands, Sweden and Germany) are the major investors and have both strong reputations in the CDM arena in addition to having assisted China in capacity development activities for CDM in early 2000. An understanding of these selection factors that potential CDM hosts use in their joint venture decisions should benefit CDM investors. This knowledge should also provide the policy and strategic level framework for future potential CDM hosts in other developing countries. - Highlights: ► CDM is the only Kyoto mechanism that links developed and developing countries. ► China is a dominant player in CDM markets with >47% of the world's 3929 projects. ► European countries are the major investors in CDM project in China. ► “Reputation of company” and “experience in CDM project in China” are crucial. ► An understanding of selection factors should benefit CDM host and investors.
CDM Baseline Construction for Vietnam National Electricity Grid
Tuyen, Tran Minh; Michaelowa, Axel
2004-01-01
For projects under the Clean Development Mechanism (CDM), a baseline has to be set to allow calculation of the greenhouse gas emissions reductions achieved. An important obstacle to CDM project development is the lack of data for baseline definition; often project developers do not have access to data and therefore incur high transaction costs to collect them. The government of Vietnam has set up all necessary institutions for CDM, wants to promote CDM projects and thus is interested to reduc...
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.
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...
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)
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.
Cosmic Acceleration and the Helicity-0 Graviton
de Rham, Claudia; Heisenberg, Lavinia; Pirtskhalava, David
2010-01-01
We explore cosmology in the decoupling limit of a non-linear covariant extension of Fierz-Pauli massive gravity obtained recently in arXiv:1007.0443. In this limit the theory is a scalar-tensor model of a unique form defined by symmetries. We find that it admits a self-accelerated solution, with the Hubble parameter set by the graviton mass. The negative pressure causing the acceleration is due to a condensate of the helicity-0 component of the massive graviton, and the background evolution, in the approximation used, is indistinguishable from the \\Lambda CDM model. Fluctuations about the self-accelerated background are stable for a certain range of parameters involved. Most surprisingly, the fluctuation of the helicity-0 field above its background decouples from an arbitrary source in the linearized theory. We also show how massive gravity can remarkably screen an arbitrarily large cosmological constant in the decoupling limit, while evading issues with ghosts. The obtained static solution is stable against ...
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.
Fitting cosmological data to the function q(z) from GR theory: modified Chaplygin gas
International Nuclear Information System (INIS)
In the Friedmann cosmology, the deceleration of the expansion q plays a fundamental role. We derive the deceleration as a function of redshift q(z) in two scenarios: CDM model and modified Chaplygin gas (MCG) model. The function for the MCG model is then fitted to the cosmological data in order to obtain the cosmological parameters that minimize χ2. We use the Fisher matrix to construct the covariance matrix of our parameters and reconstruct the q(z) function. We use Supernovae Ia, WMAP5, and BAO measurements to obtain the observational constraints. We determined the present acceleration as q0 = -0.65 +- 0.19 for the MCG model using the Union2 dataset of SNeIa, BAO, and CMB and q0 = -0.67 +- 0.17 for the Constitution dataset, BAO and CMB. The transition redshift from deceleration to acceleration was found to be around 0.80 for both datasets. We have also determined the dark energy parameter for the MCG model: ΩX0 = 0.81 +- 0.03 for the Union2 dataset and ΩX0 = 0.83 +- 0.03 using the Constitution dataset (author)
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.
Papantonopoulos, E.
2002-01-01
The aim of these lectures is to give a brief introduction to brane cosmology. After introducing some basic geometrical notions, we discuss the cosmology of a brane universe with matter localized on the brane. Then we introduce an intrinsic curvature scalar term in the bulk action, and analyze the cosmology of this induced gravity. Finally we present the cosmology of a moving brane in the background of other branes, and as a particular example, we discuss the cosmological evolution of a test b...
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...
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
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.
CDM potential of SPV pumps in India
Purohit, Pallav; Michaelowa, Axel
2005-01-01
So far, the cumulative number of renewable energy systems such as Solar Photovoltaic (SPV) irrigation pumps in the agriculture sector in India is far below their theoretical potential despite government subsidy programmes. One of the major barriers are the high costs of investments in these systems. The Clean Development Mechanism (CDM) provides industrialized countries with an incentive to invest in emission reduction projects in developing countries to achieve a reduction in CO2 emissions a...
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...
Manufacturing of nuclear power components in CDM
International Nuclear Information System (INIS)
Full text: In the nuclear research programme in India, Dr. H.J. Bhabha, the architecture of the Indian Nuclear programme felt a need for proto-type development and precision manufacturing facility to fulfill the requirements of mechanical components in establishing the manufacturing capability for the successful and self sustained nuclear programme. Centre for Design and Manufacture (CDM) hitherto known as CWS was established in 1964 to cater to the specific requirements of DAE and other associated units like ISRO, DRDO. Since then CDM has made multiple technological achievements and changes towards high quality products. The acquisition of up-to-date machines during High-Tech facility under VIII Plan project and Advance Precision Fabrication facility under IX Plan project has changed the capability of CDM towards CAD, CAM, CAE and CNC machining centres. Considering the rapid growth in the design and manufacturing, it was renamed as Centre for Design and Manufacture in March 2002, with the mission of quality output through group effort and team work
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
A New Cosmic Accelerating Scenario without Dark Energy
Lima, J A S; Costa, F E M
2012-01-01
We propose an alternative, non-singular, cosmic scenario based on gravitationally-induced particle production. The model is an attempt to evade the coincidence and cosmological constant problems of the standard model ($\\Lambda$CDM) and also to connect the early and late time accelerating stages of the Universe. Our space-time emerges from a pure initial de Sitter stage thereby providing a natural solution to the horizon problem. Subsequently, due to an instability provoked by the production of massless particles, the Universe evolves smoothly to the standard radiation dominated era thereby ending the production of radiation as required by the conformal invariance. Next, the radiation becomes subdominant with the Universe entering in the cold dark matter dominated era. Finally, the negative pressure associated with the creation of cold dark matter (CCDM model) particles accelerates the expansion and drives the Universe to a final de-Sitter stage. The late time cosmic expansion history of the CCDM model is exac...
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.
Miniati, Francesco; Ryu, Dongsu; Jones, T. W.; Kang, Hyesung
2000-01-01
We investigate the dynamical importance of a newly recognized possible source of significant feedback generated during structure formation; namely cosmic ray (CR) pressure. We present evidence for the existence of numerous shocks in the hot gas of galaxy clusters (GCs). We employ for the first time an explicit numerical treatment of CR acceleration and transport in hydro simulations of structure formation. According to our results, CRs provide an important fraction of the total pressure insid...
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.)
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...
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
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.
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.
A consistent approach to falsifying ΛCDM with rare galaxy clusters
International Nuclear Information System (INIS)
We consider methods with which to answer the question ''is any observed galaxy cluster too unusual for ΛCDM?'' After emphasising that many previous attempts to answer this question will overestimate the confidence level at which ΛCDM can be ruled out, we outline a consistent approach to these rare clusters, which allows the question to be answered. We define three statistical measures, each of which are sensitive to changes in cluster populations arising from different modifications to the cosmological model. We also 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 observational survey in which the cluster was found, which makes it an ideal proxy for ranking the relative unusualness of clusters detected by different surveys. These methods are then used on a comprehensive sample of observed galaxy clusters and we confirm that all are less than 2σ deviations from the ΛCDM expectation. Whereas we have only applied our method to galaxy clusters, it is applicable to any isolated, collapsed, halo. As motivation for future surveys, we also calculate where in the mass redshift plane the rarest halo is most likely to be found, giving information as to which objects might be the most fruitful in the search for new physics
Miniati, F; Jones, T W; Kang, H; Miniati, Francesco; Ryu, Dongsu; Kang, Hyesung
2000-01-01
We investigate the dynamical importance of a newly recognized possible source of significant feedback generated during structure formation; namely cosmic ray (CR) pressure. We present evidence for the existence of numerous shocks in the hot gas of galaxy clusters (GCs). We employ for the first time an explicit numerical treatment of CR acceleration and transport in hydro simulations of structure formation. According to our results, CRs provide an important fraction of the total pressure inside GCs, up to several tenths. This was true even at high redshift (z=2), meaning that such non-thermal component could affect the evolution of structure formation.
Dark interactions and cosmological fine-tuning
International Nuclear Information System (INIS)
Cosmological models involving an interaction between dark matter and dark energy have been proposed in order to solve the so-called coincidence problem. Different forms of coupling have been studied, but there have been claims that observational data seem to narrow (some of) them down to something annoyingly close to the ΛCDM (CDM: cold dark matter) model, thus greatly reducing their ability to deal with the problem in the first place. The smallness problem of the initial energy density of dark energy has also been a target of cosmological models in recent years. Making use of a moderately general coupling scheme, this paper aims to unite these different approaches and shed some light on whether this class of models has any true perspective in suppressing the aforementioned issues that plague our current understanding of the universe, in a quantitative and unambiguous way
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...
Bykov, A M; Durret, F
2008-01-01
Large-scale structure formation, accretion and merging processes, AGN activity produce cosmological gas shocks. The shocks convert a fraction of the energy of gravitationally accelerated flows to internal energy of the gas. Being the main gas-heating agent, cosmological shocks could amplify magnetic fields and accelerate energetic particles via the multi-fluid plasma relaxation processes. We first discuss the basic properties of standard single-fluid shocks. Cosmological plasma shocks are expected to be collisionless. We then review the plasma processes responsible for the microscopic structure of collisionless shocks. A tiny fraction of the particles crossing the shock is injected into the non-thermal energetic component that could get a substantial part of the ram pressure power dissipated at the shock. The energetic particles penetrate deep into the shock upstream producing an extended shock precursor. Scaling relations for postshock ion temperature and entropy as functions of shock velocity in strong coll...
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.
Conspiratorial cosmology - the case against the Universe
Rachen, Jörg P.; Gahlings, Ute G.
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 by an unknown interest group or lodge. We analyse possible scenarios for this conspiracy, and conclude that the belief in the existence of our ...
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.
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 ...
Viable cosmological solutions in massive bimetric gravity
International Nuclear Information System (INIS)
We find the general conditions for viable cosmological solution at the background level in bigravity models. Furthermore, we constrain the parameters by comparing to the Union 2.1 supernovae catalog and identify, in some cases analytically, the best fit parameter or the degeneracy curve among pairs of parameters. We point out that a bimetric model with a single free parameter predicts a simple relation between the equation of state and the density parameter, fits well the supernovae data and is a valid and testable alternative to ΛCDM. Additionally, we identify the conditions for a phantom behavior and show that viable bimetric cosmologies cannot cross the phantom divide
Potential of CDM in renewable projects in Malaysia
International Nuclear Information System (INIS)
The Clean Development Mechanism (CDM) is a market-based tool introduced under the Kyoto Protocol to assist developing countries achieve their sustainable development objectives and at the same time provide opportunities for developed countries to meet their greenhouse gas targets cost-effectively. Projects based on renewable sources are eligible under the CDM. Such projects are also in line with the development of the fifth fuel option in Malaysia. The paper assesses the potential of CDM in renewable energy projects in particular the grid-connected biomass power projects under the Small Renewable Energy Power (SREP) Programme. The criteria (both national and international) that have to be met for the renewable energy projects to obtain approval as a CDM projects is outlined. The additional CDM activities are elaborated. The methodology for the determination of reduction in carbon dioxide emissions is provided. The paper further investigates the impact of CDM in the promotion of renewable energy projects in Malaysia
Cline, James M.
2007-01-01
A brief review of the field of braneworld cosmology, from its inception with the large extra dimension scenario, to aspects of cosmology in warped extra dimensions, including the RS-I and RS-II models, braneworld inflation, the Goldberger-Wise mechanism, mirage cosmology, the radion-induced phase transition in RS-I, possible gravity wave signals, and the DGP model.
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...
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...
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.
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...
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 analysis of pilgrim dark energy in loop quantum cosmology
Energy Technology Data Exchange (ETDEWEB)
Jawad, Abdul [COMSATS Institute of Information Technology, Department of Mathematics, Lahore (Pakistan)
2015-05-15
The proposal of pilgrim dark energy is based on the speculation that phantom-like dark energy (with strong enough resistive force) can prevent black hole formation in the universe. We explore this phenomenon in the loop quantum cosmology framework by taking pilgrim dark energy with a Hubble horizon.We evaluate the cosmological parameters such as the Hubble parameter, the equation of state parameter, the squared speed of sound, and also cosmological planes like ω{sub θ}-ω{sub θ}{sup '} and r-s on the basis of the pilgrim dark energy parameter (u) and the interacting parameter (d{sup 2}). It is found that the values of the Hubble parameter lie in the range 74{sub -0.005}{sup +0.005}. It is mentioned here that the equation of state parameter lies within the ranges -1 -+ 0.00005 for u = 2, 1 and (-1.12,-1), (-5,-1) for u = -1,-2, respectively. Also, the ω{sub θ}-ω{sub θ}{sup '} planes provide a ΛCDM limit, and freezing and thawing regions for all cases of u. It is also interesting to mention here that the ω{sub θ}-ω{sub θ}{sup '} planes lie in the range (ω{sub θ} = 1.13{sub -0.25}{sup +0.24}, ω{sub θ}{sup '} < 1.32). In addition, the r-s planes also correspond to ΛCDM for all cases of u. Finally, it is remarked that all the above constraints of the cosmological parameters (corresponding to u = @±2,±1 and d{sup 2} = 0.2{sub -1}{sup +1}) show consistency with different observational data like Planck, WP, BAO, H{sub 0}, SNLS, and nine-year WMAP. (orig.)
Cosmological analysis of pilgrim dark energy in loop quantum cosmology
International Nuclear Information System (INIS)
The proposal of pilgrim dark energy is based on the speculation that phantom-like dark energy (with strong enough resistive force) can prevent black hole formation in the universe. We explore this phenomenon in the loop quantum cosmology framework by taking pilgrim dark energy with a Hubble horizon.We evaluate the cosmological parameters such as the Hubble parameter, the equation of state parameter, the squared speed of sound, and also cosmological planes like ωθ-ωθ' and r-s on the basis of the pilgrim dark energy parameter (u) and the interacting parameter (d2). It is found that the values of the Hubble parameter lie in the range 74-0.005+0.005. It is mentioned here that the equation of state parameter lies within the ranges -1 -+ 0.00005 for u = 2, 1 and (-1.12,-1), (-5,-1) for u = -1,-2, respectively. Also, the ωθ-ωθ' planes provide a ΛCDM limit, and freezing and thawing regions for all cases of u. It is also interesting to mention here that the ωθ-ωθ' planes lie in the range (ωθ = 1.13-0.25+0.24, ωθ' < 1.32). In addition, the r-s planes also correspond to ΛCDM for all cases of u. Finally, it is remarked that all the above constraints of the cosmological parameters (corresponding to u = @±2,±1 and d2 = 0.2-1+1) show consistency with different observational data like Planck, WP, BAO, H0, SNLS, and nine-year WMAP. (orig.)
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.
Zhang Yuan Zhong
2002-01-01
This book is one of a series in the areas of high-energy physics, cosmology and gravitation published by the Institute of Physics. It includes courses given at a doctoral school on 'Relativistic Cosmology: Theory and Observation' held in Spring 2000 at the Centre for Scientific Culture 'Alessandro Volta', Italy, sponsored by SIGRAV-Societa Italiana di Relativita e Gravitazione (Italian Society of Relativity and Gravitation) and the University of Insubria. This book collects 15 review reports given by a number of outstanding scientists. They touch upon the main aspects of modern cosmology from observational matters to theoretical models, such as cosmological models, the early universe, dark matter and dark energy, modern observational cosmology, cosmic microwave background, gravitational lensing, and numerical simulations in cosmology. In particular, the introduction to the basics of cosmology includes the basic equations, covariant and tetrad descriptions, Friedmann models, observation and horizons, etc. The ...
Pecker, Jean-Claude; Narlikar, Jayant
2011-09-01
Part I. Observational Facts Relating to Discrete Sources: 1. The state of cosmology G. Burbidge; 2. The redshifts of galaxies and QSOs E. M. Burbidge and G. Burbidge; 3. Accretion discs in quasars J. Sulentic; Part II. Observational Facts Relating to Background Radiation: 4. CMB observations and consequences F. Bouchet; 5. Abundances of light nuclei K. Olive; 6. Evidence for an accelerating universe or lack of A. Blanchard; Part III. Standard Cosmology: 7. Cosmology, an overview of the standard model F. Bernardeau; 8. What are the building blocks of our universe? K. C. Wali; Part IV. Large-Scale Structure: 9. Observations of large-scale structure V. de Lapparent; 10. Reconstruction of large-scale peculiar velocity fields R. Mohayaee, B. Tully and U. Frisch; Part V. Alternative Cosmologies: 11. The quasi-steady state cosmology J. V. Narlikar; 12. Evidence for iron whiskers in the universe N. C. Wickramasinghe; 13. Alternatives to dark matter: MOND + Mach D. Roscoe; 14. Anthropic principle in cosmology B. Carter; Part VI. Evidence for Anomalous Redshifts: 15. Anomalous redshifts H. C. Arp; 16. Redshifts of galaxies and QSOs: the problem of redshift periodicities G. Burbidge; 17. Statistics of redshift periodicities W. Napier; 18. Local abnormal redshifts J.-C. Pecker; 19. Gravitational lensing and anomalous redshifts J. Surdej, J.-F. Claeskens and D. Sluse; Panel discussion; General discussion; Concluding remarks.
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.
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...
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 ...
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
Can we distinguish early dark energy from a cosmological constant?
Shi, Difu; Baugh, Carlton M.
2016-04-01
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 halos 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% are expected.
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.
International Nuclear Information System (INIS)
This paper is devoted to 100 years after the birth of A.A. Friedman. The discovery of the class of the non-stationary cosmological solutions is the greatest scientific achievement of this man. Friedman's cosmological models lie in the foundation of the modern relativistic cosmology. It follows from the astronomical observations that the large scale structure and evolution of the Universe fit well to the predictions of these models. Friedman's work has raised, for the first time, the problem of multiplicity of cosmological solutions, the problem of selecting of one of them by comparison with the constantly improving observations. Classical (non-quantum) theoretical cosmology deals with a whole space of cosmological solutions. Under investigation are the most general properties of these solutions as well as the initial and boundary conditions which, in agreement with the observations, could lead to the set of solutions most adequately describing the observed world
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
Renewable energy: Comparison of CDM and Annex I projects
International Nuclear Information System (INIS)
Geothermal, Hydro, Solar and Wind projects located in developing (4808 CDM projects) and developed (2952 Annex I projects) are compared in terms of size (capacity – MWe), capital intensity (US$/MWe) and average investment (US$ per project). The average investment in both CDM and Annex I projects increased rapidly between 2000 and 2012. Most investment in renewable energy projects in both developed and developing countries comes from domestic sources, although the share of foreign investment has been rising for both CDM and Annex I projects. A project with foreign investors often attracts funds from multiple countries, including the host country. - Highlights: • Geothermal, Hydro, Solar and Wind CDM projects are larger and less capital intensive than similar developed country projects. • Average investment in CDM and developed country Geothermal, Hydro, Solar and Wind projects increased rapidly over 2000–2012. • Most investment in renewables projects is domestic sources, but the share of foreign investment has been rising
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.)
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...
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...
International Nuclear Information System (INIS)
This research applies both quantitative and qualitative methods to investigate stakeholder preferences towards sustainable development (SD) priorities in Clean Development Mechanism (CDM) projects. The CDM's contribution to SD is explored in the context of a biomass (rice husk) case study conducted in Thailand. Quantitative analysis ranks increasing the usage of renewable energy as the highest priority, followed by employment and technology transfer. Air pollution (dust) is ranked as the most important problem. Preference weights expressed by experts and local resident are statistically different in the cases of: employment generation; emission reductions; dust; waste disposal; and noise. Qualitative results, suggest that rice husk CDM projects contribute significantly to SD in terms of employment generation, an increase in usage of renewable energy, and transfer of knowledge. However, rice husk biomass projects create a potential negative impact on air quality. In order to ensure the environmental sustainability of CDM projects, stakeholders suggest that Thailand should cancel an Environmental Impact Assessment (EIA) exemption for CDM projects with an installed capacity below 10 MW and apply it to all CDM projects. - Highlights: → Stakeholders rank increasing the usage of renewable energy as the highest priority. → Biomass (rice husk) CDM projects create a potential negative impact on air quality. → Rice husk CDM projects cannot give an extra income to farmers. → Preference weights expressed by experts and local residents are statistically different.
Efendioglu, Akin
2012-01-01
The main purpose of this study is to design a "Courseware Development Model" (CDM) and investigate its effects on pre-service teachers' academic achievements in the field of geography and attitudes toward computer-based education (ATCBE). The CDM consisted of three components: content (C), learning theory, namely, meaningful learning (ML), and…
Energy Technology Data Exchange (ETDEWEB)
Parnphumeesup, Piya, E-mail: pp66@hw.ac.uk [International Centre for Island Technology (ICIT), Institute of Petroleum Engineering, Heriot-Watt University, Old Academy, Back Road, Stromness, Orkney KW16 3AW, Scotland (United Kingdom); Kerr, Sandy A. [International Centre for Island Technology (ICIT), Institute of Petroleum Engineering, Heriot-Watt University, Old Academy, Back Road, Stromness, Orkney KW16 3AW, Scotland (United Kingdom)
2011-06-15
This research applies both quantitative and qualitative methods to investigate stakeholder preferences towards sustainable development (SD) priorities in Clean Development Mechanism (CDM) projects. The CDM's contribution to SD is explored in the context of a biomass (rice husk) case study conducted in Thailand. Quantitative analysis ranks increasing the usage of renewable energy as the highest priority, followed by employment and technology transfer. Air pollution (dust) is ranked as the most important problem. Preference weights expressed by experts and local resident are statistically different in the cases of: employment generation; emission reductions; dust; waste disposal; and noise. Qualitative results, suggest that rice husk CDM projects contribute significantly to SD in terms of employment generation, an increase in usage of renewable energy, and transfer of knowledge. However, rice husk biomass projects create a potential negative impact on air quality. In order to ensure the environmental sustainability of CDM projects, stakeholders suggest that Thailand should cancel an Environmental Impact Assessment (EIA) exemption for CDM projects with an installed capacity below 10 MW and apply it to all CDM projects. - Highlights: > Stakeholders rank increasing the usage of renewable energy as the highest priority. > Biomass (rice husk) CDM projects create a potential negative impact on air quality. > Rice husk CDM projects cannot give an extra income to farmers. > Preference weights expressed by experts and local residents are statistically different.
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.
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)
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...
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.
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, ...
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...
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...
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.
Is there a fundamental cosmological dipole?
Perivolaropoulos, Leandros
2014-01-01
Early hints for deviation from the cosmological principle and statistical isotropy are being accumulated. After reviewing these hints, I focus on four cosmologically observed axes which appear to be either marginally consistent or in conflict with the standard ΛCDM isotropic and homogeneous cosmology. These axes are abnormally aligned with each other and include: (a) The Fine Structure Constant α Dipole (b) the Dark Energy Dipole (c) the Dark Velocity Flow and (d) the CMB Maximum Temperature Asymmetry. I also discuss a simple physical model (extended topological quintessence) that has the potential to explain the existence and alignment of these axes. The model is based on the recent formation of a global monopole with Hubble scale core by an O(3) symmetric scalar field, non-minimally coupled to electromagnetism.
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 in Poincaré gauge gravity with a pseudoscalar torsion
Lu, Jianbo; Chee, Guoying
2016-05-01
A cosmology of Poincar é gauge theory is developed, where several properties of universe corresponding to the cosmological equations with the pseudoscalar torsion function are investigated. The cosmological constant is found to be the intrinsic torsion and curvature of the vacuum universe and is derived from the theory naturally rather than added artificially, i.e. the dark energy originates from geometry and includes the cosmological constant but differs from it. The cosmological constant puzzle, the coincidence and fine tuning problem are relieved naturally at the same time. By solving the cosmological equations, the analytic cosmological solution is obtained and can be compared with the ΛCDM model. In addition, the expressions of density parameters of the matter and the geometric dark energy are derived, and it is shown that the evolution of state equations for the geometric dark energy agrees with the current observational data. At last, 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.
Edmonds, Doug; Ho, Chi man; Minic, Djordje; Ng, Y Jack; Takeuchi, Tatsu
2016-01-01
We discuss the possibility that the cold dark matter mass profiles contain information on the cosmological constant, and that such information constrains the nature of cold dark matter (CDM). We call this approach Modified Dark Matter (MDM). In particular, we examine the ability of MDM to explain the observed mass profiles of 13 galaxy clusters. Using general arguments from gravitational thermodynamics, we provide a theoretical justification for our MDM mass profile and successfully compare it to the NFW mass profiles both on cluster and galactic scales. Our results suggest that indeed the CDM mass profiles contain information about the cosmological constant in a non-trivial way.
The cosmological constant puzzle
Bass, Steven D.
2011-01-01
Abstract The accelerating expansion of the Universe points to a small positive vacuum energy density and negative vacuum pressure. A strong candidate is the cosmological constant in Einstein's equations of General Relativity. Possible contributions are zero-point energies and the condensates associated with spontaneous symmetry breaking. The vacuum energy density extracted from astrophysics is 10 56 times smaller than the value expected from quantum fields and Standard Model particle physi...
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...
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.
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...
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
Bulk viscous cosmology with causal transport theory
International Nuclear Information System (INIS)
We consider cosmological scenarios originating from a single imperfect fluid with bulk viscosity and apply Eckart's and both the full and the truncated Müller-Israel-Stewart's theories as descriptions of the non-equilibrium processes. Our principal objective is to investigate if the dynamical properties of Dark Matter and Dark Energy can be described by a single viscous fluid and how such description changes when a causal theory (Müller-Israel-Stewart's, both in its full and truncated forms) is taken into account instead of Eckart's non-causal one. To this purpose, we find numerical solutions for the gravitational potential and compare its behaviour with the corresponding ΛCDM case. Eckart's and the full causal theory seem to be disfavoured, whereas the truncated theory leads to results similar to those of the ΛCDM model for a bulk viscous speed in the interval 10−11 || cb2 ∼−8
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...
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.
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...
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.
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)
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.
International Nuclear Information System (INIS)
These lectures offer a self-contained review of the role of neutrinos in cosmology. The first part deals with the question 'What is a neutrino.' and describes in a historical context the theoretical ideas and experimental discoveries related to the different types of neutrinos and their properties. The basic differences between the Dirac neutrino and the Majorana neutrino are pointed out and the evidence for different neutrino 'flavours', neutrino mass, and neutrino oscillations is discussed. The second part summarizes current views on cosmology, particularly as they are affected by recent theoretical and experimental advances in high-energy particle physics. Finally, the close relationship between neutrino physics and cosmology is brought out in more detail, to show how cosmological constraints can limit the various theoretical possibilities for neutrinos and, more particularly, how increasing knowledge of neutrino properties can contribute to our understanding of the origin, history, and future of the Universe. The level is that of the beginning graduate student. (orig.)
Turner, M S
1998-01-01
For two decades the hot big-bang model as been referred to as the standard cosmology -- and for good reason. For just as long cosmologists have known that there are fundamental questions that are not answered by the standard cosmology and point to a grander theory. The best candidate for that grander theory is inflation + cold dark matter; it can extend our understanding of the Universe back to 10^-32 sec. There is now prima facie evidence for the two basic tenets of this new paradigm: flat Universe and scale-invariant spectrum of Gaussian density perturbations, and an avalanche of telling cosmological observations is coming. If inflation + cold dark matter is correct, then there are new, fundamental questions to be answered, most notably the nature of the dark energy that seems to account for 60% of the critical density and how inflation fits into a unified theory of the forces and particles. These are exciting times in cosmology!
Lesgourgues, Julien; Miele, Gennaro; Pastor, Sergio
2013-01-01
The role that neutrinos have played in the evolution of the Universe is the focus of one of the most fascinating research areas that has stemmed from the interplay between cosmology, astrophysics and particle physics. In this self-contained book, the authors bring together all aspects of the role of neutrinos in cosmology, spanning from leptogenesis to primordial nucleosynthesis, their role in CMB and structure formation, to the problem of their direct detection. The book starts by guiding the reader through aspects of fundamental neutrino physics, such as the standard cosmological model and the statistical mechanics in the expanding Universe, before discussing the history of neutrinos in chronological order from the very early stages until today. This timely book will interest graduate students and researchers in astrophysics, cosmology and particle physics, who work with either a theoretical or experimental focus.
Cosmology with photometric redshift surveys
Blake, C; Blake, Chris; Bridle, Sarah
2004-01-01
We explore the utility of future photometric redshift imaging surveys for delineating the large-scale structure of the Universe, and assess the resulting constraints on the cosmological model. We perform two complementary types of analysis: (1) We quantify the statistical confidence and accuracy with which such surveys will be able to detect and measure characteristic features in the clustering power spectrum such as the acoustic oscillations and the turnover, in a model-independent fashion. For example, we show that a 10000 sq deg imaging survey with depth r = 22.5 and photometric redshift accuracy dz/(1+z) = 0.03 will detect the acoustic oscillations with 99.9% confidence, measuring the associated cosmological scale with 2% precision. Such a survey will also detect the turnover with 95% confidence, determining the corresponding scale with 20% accuracy. (2) By assuming a Lambda-CDM cosmology we calculate the confidence with which a non-zero baryon fraction can be deduced from such future surveys. After margi...
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.
Brane cosmology with curvature corrections
International Nuclear Information System (INIS)
We study the cosmology of the Randall-Sundrum brane-world where the Einstein-Hilbert action is modified by curvature correction terms: a four-dimensional scalar curvature from induced gravity on the brane, and a five-dimensional Gauss-Bonnet curvature term. The combined effect of these curvature corrections to the action removes the infinite-density big bang singularity, although the curvature can still diverge for some parameter values. A radiation brane undergoes accelerated expansion near the minimal scale factor, for a range of parameters. This acceleration is driven by the geometric effects, without an inflation field or negative pressures. At late times, conventional cosmology is recovered. (author)
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
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...
A Test of Cosmological Models using high-z Measurements of H(z)
Melia, Fulvio
2015-01-01
The recently constructed Hubble diagram using a combined sample of SNLS and SDSS-II Type Ia SNe, and an application of the Alcock-Paczynski (AP) test using model-independent Baryon Acoustic Oscillation data, have suggested that the principal constraint underlying the cosmic expansion is the total equation-of-state of the cosmic fluid, rather than that of its dark energy. These studies have focused on the critical redshift range (0 < z < 2) within which the transition from decelerated to accelerated expansion is thought to have occurred, and they suggest that the cosmic fluid has zero active mass, consistent with a constant expansion rate. The evident impact of this conclusion on cosmological theory calls for an independent confirmation. In this paper, we carry out this crucial one-on-one comparison between the R_h=ct Universe (an FRW cosmology with zero active mass) and wCDM/LCDM, using the latest high-z measurements of H(z). Whereas the Type Ia SNe yield the integrated luminosity distance, while the AP...
Modified geodetic brane cosmology
International Nuclear Information System (INIS)
We explore the cosmological implications provided by the geodetic brane gravity action corrected by an extrinsic curvature brane term, describing a codimension-1 brane embedded in a 5D fixed Minkowski spacetime. In the geodetic brane gravity action, we accommodate the correction term through a linear term in the extrinsic curvature swept out by the brane. We study the resulting geodetic-type equation of motion. Within a Friedmann–Robertson–Walker metric, we obtain a generalized Friedmann equation describing the associated cosmological evolution. We observe that, when the radiation-like energy contribution from the extra dimension is vanishing, this effective model leads to a self-(non-self)-accelerated expansion of the brane-like universe in dependence on the nature of the concomitant parameter β associated with the correction, which resembles an analogous behaviour in the DGP brane cosmology. Several possibilities in the description for the cosmic evolution of this model are embodied and characterized by the involved density parameters related in turn to the cosmological constant, the geometry characterizing the model, the introduced β parameter as well as the dark-like energy and the matter content on the brane. (paper)
Weighted ABC: a new strategy for cluster strong lensing cosmology with simulations
Killedar, Madhura; Fabjan, Dunja; Dolag, Klaus; Granato, Gian Luigi; Meneghetti, Massimo; Planelles, Susana; Ragone-Figueroa, Cinthia
2015-01-01
Comparisons between observed and predicted strong lensing properties of galaxy clusters have been routinely used to claim either tension or consistency with $\\Lambda$CDM cosmology. However, standard approaches to such cosmological tests are unable to quantify the preference for one cosmology over another. We advocate using a `weighted' variant of approximate Bayesian computation (ABC), whereby the parameters of the scaling relation between Einstein radii and cluster mass, $\\alpha$ and $\\beta$, are treated as summary statistics. We demonstrate, for the first time, a method of estimating the likelihood of the data under the $\\Lambda$CDM framework, using the X-ray selected $z>0.5$ MACS clusters as a case in point and employing both N-body and hydrodynamic simulations of clusters. We investigate the uncertainty in the calculated likelihood, and consequential ability to compare competing cosmologies, that arises from incomplete descriptions of baryonic processes, discrepancies in cluster selection criteria, redshi...
Colliders as a simultaneous probe of supersymmetric dark matter and Terascale cosmology
Barenboim, G; Barenboim, Gabriela; Lykken, Joseph
2006-01-01
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. ...
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.
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}.
International Nuclear Information System (INIS)
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 ∑ mν, wCDM r Neff, wCDM r ∑ mν Neff, and wCDM r Neff mν,sterileeff 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, ∑ mν, Neff, and mν,sterileeff
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 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.
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.
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.
How does pressure gravitate? Cosmological constant problem confronts observational cosmology
Narimani, Ali; Afshordi, Niayesh; Scott, Douglas
2014-08-01
An important and long-standing puzzle in the history of modern physics is the gross inconsistency between theoretical expectations and cosmological observations of the vacuum energy density, by at least 60 orders of magnitude, otherwise known as the cosmological constant problem. A characteristic feature of vacuum energy is that it has a pressure with the same amplitude, but opposite sign to its energy density, while all the precision tests of General Relativity are either in vacuum, or for media with negligible pressure. Therefore, one may wonder whether an anomalous coupling to pressure might be responsible for decoupling vacuum from gravity. We test this possibility in the context of the Gravitational Aether proposal, using current cosmological observations, which probe the gravity of relativistic pressure in the radiation era. Interestingly, we find that the best fit for anomalous pressure coupling is about half-way between General Relativity (GR), and Gravitational Aether (GA), if we include Planck together with WMAP and BICEP2 polarization cosmic microwave background (CMB) observations. Taken at face value, this data combination excludes both GR and GA at around the 3 σ level. However, including higher resolution CMB observations (``highL'') or baryonic acoustic oscillations (BAO) pushes the best fit closer to GR, excluding the Gravitational Aether solution to the cosmological constant problem at the 4- 5 σ level. This constraint effectively places a limit on the anomalous coupling to pressure in the parametrized post-Newtonian (PPN) expansion, ζ4 = 0.105 ± 0.049 (+highL CMB), or ζ4 = 0.066 ± 0.039 (+BAO). These represent the most precise measurement of this parameter to date, indicating a mild tension with GR (for ΛCDM including tensors, with 0ζ4=), and also among different data sets.
How does pressure gravitate? Cosmological constant problem confronts observational cosmology
International Nuclear Information System (INIS)
An important and long-standing puzzle in the history of modern physics is the gross inconsistency between theoretical expectations and cosmological observations of the vacuum energy density, by at least 60 orders of magnitude, otherwise known as the cosmological constant problem. A characteristic feature of vacuum energy is that it has a pressure with the same amplitude, but opposite sign to its energy density, while all the precision tests of General Relativity are either in vacuum, or for media with negligible pressure. Therefore, one may wonder whether an anomalous coupling to pressure might be responsible for decoupling vacuum from gravity. We test this possibility in the context of the Gravitational Aether proposal, using current cosmological observations, which probe the gravity of relativistic pressure in the radiation era. Interestingly, we find that the best fit for anomalous pressure coupling is about half-way between General Relativity (GR), and Gravitational Aether (GA), if we include Planck together with WMAP and BICEP2 polarization cosmic microwave background (CMB) observations. Taken at face value, this data combination excludes both GR and GA at around the 3 σ level. However, including higher resolution CMB observations (''highL'') or baryonic acoustic oscillations (BAO) pushes the best fit closer to GR, excluding the Gravitational Aether solution to the cosmological constant problem at the 4- 5 σ level. This constraint effectively places a limit on the anomalous coupling to pressure in the parametrized post-Newtonian (PPN) expansion, ζ4 = 0.105 ± 0.049 (+highL CMB), or ζ4 = 0.066 ± 0.039 (+BAO). These represent the most precise measurement of this parameter to date, indicating a mild tension with GR (for ΛCDM including tensors, with 0ζ4=), and also among different data sets
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.
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...
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.)
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...
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...
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...
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.
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_{\
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
International Nuclear Information System (INIS)
A brane universe moving in a curved higher dimensional bulk space is considered. The motion induces a cosmological evolution on the universe brane that is indistinguishable from a similar one induced by matter density on the brane. The phenomenological implications of such an idea are discussed. Various mirage energy densities are found, corresponding to dilute matter driving the cosmological expansion, many having superluminal properties vertical bar w vertical bar >1 or violating the positive energy condition. It is shown that energy density due to the world-volume fields is nicely incorporated into the picture. It is also pointed out that the initial singularity problem is naturally resolved in this context. (author)
International Nuclear Information System (INIS)
Observations indicate the presence of a magnetic field at galactic and cosmological scales. However, the origin of these magnetic fields is not well understood. There is enough motivation to look into the primordial origin of magnetic field, which essentially requires the breaking of conformal invariance of Maxwell's theory. Several mechanisms to generate primordial magnetic field have been proposed. A brief overview of those models has been presented. Central problem of the models within inflationary paradigm has been addressed. Possibilities to generate primordial magnetic field beyond inflationary framework are mentioned. A toy model for bouncing cosmology has been presented to understand the idea of magnetogenesis in such models
Ringwald, A.
2012-01-01
In this master's thesis we study the cosmological consequences of the new scalar field, the axion, that appears in the U(1)_PQ extension of the standard model of particle physics. We start by presenting some essential fragments of the standard model of Big Bang cosmology, that are needed when we describe the evolution of the axion field in the early Universe. We also review the basics of phase transitions in the early Universe, and go through the creation and evolution of the topological defe...
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.
Bouncing cosmologies with viscous fluids
Singh, T.; Chaubey, R.; Singh, Ashutosh
2016-03-01
The bounce in viscous fluid cosmology with inhomogeneous viscous fluids in Friedman-Robertson-Walker (FRW) space-time has been investigated. Different forms for the scale factor have been considered. The general features of the fluids which realize them and the possibility to have an acceleration after the bounce have been 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.
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.
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.)
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 .
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.
Marsh, David J E
2015-01-01
Axions comprise a broad class of particles that can play a major role in explaining the unknown aspects of cosmology. They are also extraordinarily well-motivated within high energy physics, and so axion cosmology offers us a unique view onto these theories. I present a comprehensive and pedagogical view on the cosmology and astrophysics of axion-like particles, starting from inflation and progressing via the CMB and structure formation up to the present-day Universe. I briefly review the motivation and models for axions in particle physics and string theory. The primary focus is on the population of ultralight axions created via vacuum realignment, and its role as a dark matter (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 l...
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.
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...
Dark Interactions and Cosmological Fine-Tuning
Quartin, Miguel; Joras, Sergio E; Reis, Ribamar R R; Waga, Ioav
2008-01-01
Cosmological models involving an interaction between dark matter and dark energy have been proposed in order to solve the so-called coincidence problem. Different forms of coupling have been studied, but there have been claims that observational data seem to narrow (some of) them down to something annoyingly close to the $\\Lambda$CDM model, thus greatly reducing their ability to deal with the problem in the first place. The smallness problem of the initial energy density of dark energy has also been a target of cosmological models in recent years. Making use of a moderately general coupling scheme, this paper aims to unite these different approaches and shed some light as to whether this class of models has any true perspective in suppressing the aforementioned issues that plague our current understanding of the universe, in a quantitative and unambiguous way.
Planck 2013 results. XVI. Cosmological parameters
Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bobin, J.; Bock, J. J.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bridges, M.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cappellini, B.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R.-R.; Chen, X.; Chiang, H. C.; Chiang, L.-Y.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Couchot, F.; 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.; Delouis, J.-M.; Désert, F.-X.; Dickinson, C.; Diego, J. M.; Dolag, K.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Dunkley, J.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Gaier, T. C.; Galeotta, S.; Galli, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Haissinski, J.; Hamann, J.; Hansen, F. K.; Hanson, D.; Harrison, D.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hou, Z.; Hovest, W.; Huffenberger, K. M.; Jaffe, A. H.; Jaffe, T. R.; Jewell, J.; 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.; Laureijs, R. J.; Lawrence, C. R.; Leach, S.; Leahy, J. P.; Leonardi, R.; León-Tavares, J.; Lesgourgues, J.; Lewis, A.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maffei, B.; Maino, D.; Mandolesi, N.; Maris, M.; Marshall, D. J.; Martin, P. G.; Martínez-González, E.; Masi, S.; Massardi, M.; Matarrese, S.; Matthai, F.; Mazzotta, P.; Meinhold, P. R.; Melchiorri, A.; Melin, J.-B.; Mendes, L.; Menegoni, E.; 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.; O'Dwyer, I. J.; Osborne, S.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Pearson, D.; Pearson, T. J.; Peiris, H. V.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Platania, P.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Popa, L.; Poutanen, T.; Pratt, G. W.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Roudier, G.; Rowan-Robinson, M.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Spencer, L. D.; Starck, J.-L.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sureau, F.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Tavagnacco, D.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Türler, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; White, M.; White, S. D. M.; Wilkinson, A.; Yvon, D.; Zacchei, A.; Zonca, A.
2014-11-01
This paper presents the first cosmological results based on Planck measurements of the cosmic microwave background (CMB) temperature and lensing-potential power spectra. We find that the Planck spectra at high multipoles (ℓ ≳ 40) are extremely well described by the standard spatially-flat six-parameter ΛCDM cosmology with a power-law spectrum of adiabatic scalar perturbations. Within the context of this cosmology, the Planck data determine the cosmological parameters to high precision: the angular size of the sound horizon at recombination, the physical densities of baryons and cold dark matter, and the scalar spectral index are estimated to be θ∗ = (1.04147 ± 0.00062) × 10-2, Ωbh2 = 0.02205 ± 0.00028, Ωch2 = 0.1199 ± 0.0027, and ns = 0.9603 ± 0.0073, respectively(note that in this abstract we quote 68% errors on measured parameters and 95% upper limits on other parameters). For this cosmology, we find a low value of the Hubble constant, H0 = (67.3 ± 1.2) km s-1 Mpc-1, and a high value of the matter density parameter, Ωm = 0.315 ± 0.017. These values are in tension with recent direct measurements of H0 and the magnitude-redshift relation for Type Ia supernovae, but are in excellent agreement with geometrical constraints from baryon acoustic oscillation (BAO) surveys. Including curvature, we find that the Universe is consistent with spatial flatness to percent level precision using Planck CMB data alone. We use high-resolution CMB data together with Planck to provide greater control on extragalactic foreground components in an investigation of extensions to the six-parameter ΛCDM model. We present selected results from a large grid of cosmological models, using a range of additional astrophysical data sets in addition to Planck and high-resolution CMB data. None of these models are favoured over the standard six-parameter ΛCDM cosmology. The deviation of the scalar spectral index from unity isinsensitive to the addition of tensor modes and to
Non-linear Fields in Generalized Cosmologies
Fasiello, Matteo
2016-01-01
The perturbative approach to structure formation has recently received a lot of attention in the literature. In such setups the final predictions for observables like the power spectrum is often derived under additional approximations such as a simplified time dependence. Here we provide all-order perturbative integral solutions for density and velocity fields in generalized cosmologies. We go beyond the standard results based on extending the EdS-like approximations. As an illustrative example, we apply our findings to the calculation of the one-loop power spectrum. We find corrections close to $1\\%$ in the mildly non-linear regime of $\\Lambda$CDM cosmologies for the density power spectrum, while in the case of the density-momentum power spectrum effects can reach up to $1.5\\%$ for $k\\sim 0.2h/$Mpc.
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.
Dynamics of interacting dark energy model in Einstein and Loop Quantum Cosmology
Chen, Songbai; Wang, Bin(Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, 200240, China); Jing, Jiliang
2008-01-01
We investigate the background dynamics when dark energy is coupled to dark matter in the universe described by Einstein cosmology and Loop Quantum Cosmology. We introduce a new general form of dark sector coupling, which presents us a more complicated dynamical phase space. Differences in the phase space in obtaining the accelerated scaling attractor in Einstein cosmology and Loop Quantum Cosmology are disclosed.
Formation of Primordial Stars in a Lambda-CDM Universe
Energy Technology Data Exchange (ETDEWEB)
Yoshida, Naoki; /Nagoya U.; Omukai, Kazuyuki; /Tokyo, Astron. Observ.; Hernquist, Lars; /Harvard-Smithsonian Ctr. Astrophys.; Abel, Tom; /KIPAC, Menlo Park
2006-06-09
Primordial stars are formed from a chemically pristine gas consisting of hydrogen and helium. They are believed to have been born at some early epoch in the history of the Universe and to have enriched the interstellar medium with synthesized heavy elements before the emergence of ordinary stellar populations. We study the formation of the first generation of stars in the standard cold dark matter model. We follow the gravitational collapse and thermal evolution of primordial gas clouds within early cosmic structures using very high-resolution, cosmological hydrodynamic simulations. Our simulation achieves a dynamic range of {approx} 10{sup 10} in length scale. With accurate treatment of atomic and molecular physics, it allows us to study the chemo-thermal evolution of primordial gas clouds to densities up to {rho} {approx} 2 x 10{sup -8}g cm{sup -3} (n{sub H} {approx} 10{sup 16}cm{sup -3}) without assuming any a priori equation of state; a six orders of magnitudes improvement over previous three-dimensional calculations. We implement an extensive chemistry network for hydrogen, helium and deuterium. All the relevant atomic and molecular cooling and heating processes, including cooling by collision-induced continuum emission, are implemented. For calculating optically thick H{sub 2} cooling at high densities, we use the Sobolev method (Sobolev 1960) and evaluate the molecular line opacities for a few hundred lines. We validate the accuracy of the method by performing a spherical collapse test and comparing the results with those of accurate one-dimensional calculations that treat the line radiative transfer problem in a fully self-consistent manner. We then perform a cosmological simulation adopting the standard {Lambda}CDM model. Dense gas clumps are formed at the centers of low mass ({approx} 10{sup 5-6}M{sub {circle_dot}}) dark matter halos at redshifts z {approx} 20, and they collapse gravitationally when the cloud mass exceeds a few hundred solar masses. To
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.
Information Gains from Cosmological Probes
Grandis, S; Refregier, A; Amara, A; Nicola, A
2015-01-01
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 $\\Lambda$CDM 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 ...
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 ...
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
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...
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
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. (author)
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
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 ...
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.
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.
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?
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 ...
Bonanno, Alfio
2011-01-01
We discuss a mechanism that induces a time-dependent vacuum energy on cosmological scales. It is based on the instability induced renormalization triggered by the low energy quantum fluctuations in a Universe with a positive cosmological constant. We employ the dynamical systems approach to study the qualitative behavior of Friedmann-Robertson-Walker cosmologies where the cosmological constant is dynamically evolving according with this nonperturbative scaling at low energies. It will be shown that it is possible to realize a "two regimes" dark energy phases, where an unstable early phase of power-law evolution of the scale factor is followed by an accelerated expansion era at late times.
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...
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.
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…
Constraining scalar field dark energy with cosmological observations
Samushia, Lado
2009-01-01
High precision cosmological observations in last decade suggest that about 70% of our universe's energy density is in so called "Dark Energy" (DE). Observations show that DE has negative effective pressure and therefore unlike conventional energy sources accelerates the cosmic expansion instead of decelerating it. DE is highly uniform and has become a dominant component only recently. The simplest candidate for DE is the time-independent cosmological constant $\\Lambda$. Although successful in fitting available data, the cosmological constant model has a number of theoretical shortcomings and because of that alternative models of DE are considered. In one such scenario a cosmological scalar field that slowly rolls down its potential acts like a time-dependent cosmological constant. I have used different independent cosmological data sets to constrain the time dependence of DE's energy density in the framework of the slowly-rolling cosmological scalar field model. Present data favors a time-independent cosmolog...
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.
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.)
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...
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
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.
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.
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.
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.
Zimdahl, Winfried; Pavón, Diego
2002-01-01
We show that with the help of a suitable coupling between dark energy and cold dark matter it is possible to reproduce any scaling solution $\\rho _{X}\\propto \\rho_{M}a^{\\xi}$, where $\\rho_{X}$ and $\\rho_{M}$ are the densities of dark energy and dark matter, respectively. We demonstrate how the case $\\xi = 1$ alleviates the coincidence problem. Future observations of supernovae at high redshift as well as quasar pairs which are planned to discriminate between different cosmological models will...
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
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.
Wickramasinghe, N. C.; Hoyle, Fred
1998-07-01
The central regions of galaxies could provide the most promising venues for the large-scale synthesis of prebiotic molecules by Miller-Urey type processes.Exploding supermassive stars would produce the basic chemical elements necessary to form molecules in high-density mass flows under near-thermodynamic conditions. Such molecules are then acted upon by X-rays in a manner that simulates the conditions required for Miller-Urey type processing. The Miller-Urey molecular products could initially lead to the origination and dispersal of microbial life on a cosmological scale. Thereafter the continuing production of such molecules would serve as the feedstock of life.
International Nuclear Information System (INIS)
Networks often represent systems that do not have a long history of study in traditional fields of physics; albeit, there are some notable exceptions, such as energy landscapes and quantum gravity. Here, we consider networks that naturally arise in cosmology. Nodes in these networks are stationary observers uniformly distributed in an expanding open Friedmann–Lemaître–Robertson–Walker universe with any scale factor and two observers are connected if one can causally influence the other. We show that these networks are growing Lorentz-invariant graphs with power-law distributions of node degrees. These networks encode maximum information about the observable universe available to a given observer. (paper)
Magnetohydrodynamic cosmologies
International Nuclear Information System (INIS)
We analyse a class of cosmological models in magnetohydrodynamic regime extending and completing the results of a previous paper. The material content of the models is a perfect fluid plus electromagnetic fields. The fluid is neutral in average but admits an electrical current which satisfies Ohm's law. All models fulfil the physical requirements of near equilibrium thermodynamics and can be favourably used as a more realistic description of the interior of a collapsing star in a magnetohydrodynamic regime with or without a magnetic field. (author)
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.
Recent Developments in Cosmology and Nucleochronometry
International Nuclear Information System (INIS)
Cosmology is currently entering a new phase of comprehensiveness, precision and confidence. Recent developments in theoretical and observational cosmology (including accelerating expansion, cosmic micro wave background anisotropy and nonzero-mass neutrino oscillations) and nucleochonometry are herein reviewed, presenting the latest values of quasar red-shift, cosmological parameters in the standard model (with concentration up on the Hubble constant and the age of the Universe) and dating information from nuclear astrophysics. The methods and findings of nucleochronology, in the main based up on stellar r-process neutron capture rate data relevant to, e.g., 137Re/137Os chronometry, Th/Eu abundance ratios and Th or U chronometry techniques are discussed in detail. Recent findings concerning the accelerated expansion of the Universe are presented, with consideration given to cosmological implications of, e.g., dark energy, exotic dark matter, cosmic strings and supergravity . In conclusion, some remaining current problems and uncertainties are briefly noted. (author)
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.
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...
Carloni, Sante; Nojiri, Shin'ichi; Odintsov, Sergei D; Oksanen, Markku; Tureanu, Anca
2010-01-01
We propose the most general modified first-order Ho\\v{r}ava-Lifshitz gravity, whose action does not contain time derivatives higher than the second order. The Hamiltonian structure of this theory is studied in all the details in the case of the spatially-flat FRW space-time, demonstrating many of the features of the general theory. It is shown that, with some plausible assumptions, including the projectability of the lapse function, this model is consistent. As a large class of such theories, the modified $F(R)$ Ho\\v{r}ava-Lifshitz gravity is introduced. The study of its ultraviolet properties shows that its $z=3$ version seems to be renormalizable in the same way as the original Ho\\v{r}ava-Lifshitz proposal. The Hamiltonian analysis of the modified $F(R)$ Ho\\v{r}ava-Lifshitz gravity shows that it is in general a consistent theory. The $F(R)$ gravity action is also studied in the fixed-gauge form, where the appearance of a scalar field is particularly illustrative. Then the spatially-flat FRW cosmology for th...
International Nuclear Information System (INIS)
When the common ground between particle physics, astrophysics and cosmology started to become a developing area, the Institute for Nuclear Research (INR) of the Russian Academy of Sciences had the foresight in 1981 to institute the Baksan Schools on Particles and Cosmology. This now traditional event, held biannually in the Baksan Valley, has gone on to attract international participation. The site is close to the INR Baksan Neutrino Observatory with its underground and surface installations, including the SAGE gallium solar neutrino detector, the Underground Scintillation Telescope, and the 'Carpet' extensive air shower array. Participation is mainly from experimentalists working in non accelerator particle physics and particle astrophysics. The most recent School, held from April 21 to 28, began with an opening address by INR Director V. A. Matveev. J.Frieman reviewed standard big bang cosmology, emphasizing how the recent COBE results and the observations of large scale galaxy clustering fit into a standard cosmology framework. For inflationary cosmology, he showed how different models may be tested through their predictions for large-scale galactic structure and for cosmic microwave background anisotropy. A.Stebbins presented details of the large scale distribution of galaxies which, combined with velocity information and microwave background anisotropy data, provide strong constraints on theories of the origin of primordial inhomogeneities. Inflation requires, and theories of the large scale structure strongly favour the critical value for the cosmic mass density, while, as D.Seckel explained in his lecture on nucleosynthesis and abundances of the light elements, the baryon contribution to this density has to be tens of times smaller. A general review on the observational evidence for dark matter, dark matter particle candidates and the strategy of dark matter searches was given by I. Tkachev, who stressed the gravitational microlensing MACHO
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
Analysis of technology transfer in CDM projects: An update
International Nuclear Information System (INIS)
The clean development mechanism (CDM) contributes to technology transfer by financing emission reduction projects using technologies not available in the host countries. This paper provides the most comprehensive analysis of technology transfer in the CDM to-date, covering 3296 registered and proposed projects. Roughly 36% of the projects accounting for 59% of the annual emission reductions claim to involve technology transfer. Technology transfer is more common for larger projects and projects with foreign participants. Technology transfer is very heterogeneous across project types and usually involves both knowledge and equipment. As the number of projects increases, technology transfer occurs beyond the individual projects. This is observed for several of the most common project types in China and Brazil with the result that the rate of technology transfer for new projects in those countries has fallen significantly.
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.
Defining Investment Additionality for CDM projects - practical approaches
International Nuclear Information System (INIS)
The environmental integrity of the CDM under the Kyoto Protocol depends on the possibility to avoid giving emission credits to projects that would have happened anyway. Whether and how 'Investment Additionality' of CDM projects has to be determined is currently a part of climate negotiations. We discuss the rationale of companies to invest in projects and analyse possible criteria to determine Investment Additionality from a theoretical point of view. Differences in the type of investment call for the application of different criteria. Although some criteria are better than others, no single criterion can outweigh the others in all respects. We therefore suggest a scheme for additionality testing that aims at matching types of investment and criteria in a sensible way. Criteria are evaluated on the grounds of robustness to manipulation, degree of coverage and appropriateness for testing the investment decision under consideration
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...
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.
Confronting the concordance model of cosmology with Planck data
Hazra, Dhiraj Kumar
2014-01-01
We confront the concordance (standard) model of cosmology, the spatially flat $\\Lambda$CDM Universe with power-law form of the primordial spectrum with Planck CMB angular power spectrum data searching for possible smooth deviations beyond the flexibility of the standard model. The departure from the concordance cosmology is modeled in the context of Crossing statistic and statistical significance of this deviation is used as a measure to test the consistency of the standard model to the Planck data. Derived Crossing functions suggest the presence of some broad features in angular spectrum beyond the expectations of the concordance model. Our results indicate that the concordance model of cosmology is consistent to the Planck data only at 2 to 3$\\sigma$ confidence level if we allow smooth deviations from the angular power spectrum given by the concordance model. This might be due to random fluctuations or may hint towards smooth features in the primordial spectrum or departure from another aspect of the standa...
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...
Dark Energy and the New Cosmology
Turner, Michael S.
2001-01-01
A successor to the standard hot big-bang cosmology is emerging. It greatly extends the highly successful hot big-bang model. A key element of the New Standard Cosmology is dark energy, the causative agent for accelerated expansion. Dark energy is just possibly the most important problem in all of physics. The only laboratory up to the task of studying dark energy is the Universe itself.
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⊙.
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.
International Nuclear Information System (INIS)
This paper addresses activity a) an analysis of international CDM experiences and its potential contribution to the LAC region. The paper begins with a section describing the basic principles of the CDM and retrieves the lessons learned from the first two years of the CDM operation. This is followed by a more detailed review in section 2 of the on-going baseline and monitoring methodology approval process. In section 3, the development value of the CDM is explored. Section 4 describes the current CDM markets, while section 5 reviews the response of host countries to the CDM outside the LAC region. Section 6 describes the various capacity building programs established by Annex 1 countries to support the CDM. In each of the first 6 sections, implications for the LAC region are identified. Section 7 brings these conclusions together into a concise summary. (The author)
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.
Addressing carbon Offsetters’ Paradox: Lessons from Chinese wind CDM
International Nuclear Information System (INIS)
The clean development mechanism (CDM) has been a leading international carbon market and a driving force for sustainable development. But the eruption of controversy over offsets from Chinese wind power in 2009 exposed cracks at the core of how carbon credits are verified in the developing economies. The Chinese wind controversy therefore has direct implications for the design and negotiation of any successor to the Kyoto Protocol or future market-based carbon regimes. In order for carbon markets to avoid controversy and function effectively, the lessons from the Chinese wind controversy should be used to implement key reforms in current and future carbon policy design. The paper examines the application of additionality in the Chinese wind power market and draws implications for the design of effective global carbon offset policy. It demonstrates the causes of the wind power controversy, highlights underlying structural flaws, in how additionality is applied in China, the Offsetters' Paradox, and charts a reform path that can strengthen the credibility of global carbon markets. - Highlights: • We investigated 143 Chinese wind CDM projects by the eruption of the additionality controversy. • We examined the application of additionality in the Chinese wind power market. • We drew implications for the design of effective global carbon offset policy. • The underlying structural flaws of CDM, the Offsetters′ Paradox, was discussed. • We charted a reform path that can strengthen the credibility of global carbon markets
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...
Orbital parameters of infalling satellite haloes in the hierarchical $\\Lambda$CDM model
Jiang, Lilian; Sawala, Till; Frenk, Carlos S
2014-01-01
We present distributions of orbital parameters of infalling satellites of $\\Lambda$CDM haloes in the mass range $10^{12}-10^{14}$M$_\\odot$, which represent the initial conditions for the subsequent evolution of substructures within the host halo. We use merger trees constructed in a high resolution cosmological N-body simulation to trace satellite haloes, and identify the time of infall. We find signficant trends in the distribution of orbital parameters with both the host halo mass and the ratio of satellite-to-host halo masses. For all host halo masses, satellites whose infall mass is a larger fraction of the host halo mass have more eccentric, radially biased orbits. At fixed satellite-to-host halo mass ratio, high mass haloes are biased towards accreting satellites on slightly more biased orbits. To charactise the orbital distributions fully requires fitting the correlated bivariate distribution of two chosen orbital parameters (e.g. radial and tangential velocity or energy and angular momentu). We provid...
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
An introduction to cosmological inflation
International Nuclear Information System (INIS)
An introductory account is given of the inflationary cosmology, which postulates a period of accelerated expansion during the Universe's earliest stages. The historical motivation is briefly outlined, and the modelling of the inflationary epoch explained. The most important aspect of inflation is that it provides a possible model for the origin of structure in the Universe, and key results are reviewed, along with a discussion of the current observational situation and outlook. (author)
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...
GRB neutrinos, Lorenz Invariance Violation and the influence of background cosmology
Biesiada, Marek
2007-01-01
Modern ideas in quantum gravity predict the possibility of Lorenz Invariance Violation (LIV) manifested e.g. by energy dependent modification of standard relativistic dispersion relation. In a recent paper Jacob and Piran proposed that time of flight delays in high energy neutrinos emitted by gamma ray bursts (GRBs) located at cosmological distances can become a valuable tool for setting limits on LIV theories. However, current advances in observational cosmology suggest that our Universe is dominated by dark energy with relatively little guidance on its nature thus leading to several cosmological scenarios compatible with observations. In this paper we raise the issue of how important, in the context of testing LIV theories, is our knowledge of background cosmological model. Specifically we calculate expected time lags for high-energy (100 TeV) neutrinos in different cosmological models. Out of many particular models of dark energy we focus on five: $\\Lambda$CDM, quintessence, quintessence with time varying ...
An analytic cosmological solution of Poincare gauge gravity with a pseudoscalar torsion
Lu, Jianbo
2016-01-01
A cosmology of Poincare gauge theory is developed, and its analytic solution is obtained. The calculation results agree with observational data and can be compared with the $\\Lambda $CDM model. The cosmological constant puzzle, the coincidence and fine tuning problem are relieved 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.
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 $(w = -1/3)$,...
Directory of Open Access Journals (Sweden)
Carroll Sean M.
2001-01-01
Full Text Available This is a review of the physics and cosmology of the cosmological constant. Focusing on recent developments, I present a pedagogical overview of cosmology in the presence of a cosmological constant, observational constraints on its magnitude, and the physics of a small (and potentially nonzero vacuum energy.
Cosmological Parameters from the 2003 flight of BOOMERANG
MacTavish, C J; Bock, J J; Bond, J R; Borrill, J; Boscaleri, A; Cabella, P; Contaldi, C R; Crill, B P; De Bernardis, P; De Gasperis, G; De Oliveira-Costa, A; De Troia, G; Stefano, G D; Hivon, E; Jaffe, A H; Jones, W C; Kisner, T S; Lange, A E; Lewis, A M; Masi, S; Mauskopf, P D; Melchiorri, A; Montroy, T E; Natoli, P; Netterfield, C B; Pascale, E; Piacentini, F; Pogosyan, D; Polenta, G; Prunet, S; Ricciardi, S; Romeo, G; Ruhl, J E; Santini, P; Tegmark, M; Veneziani, M; Vittorio, N
2005-01-01
We present the cosmological parameters from the CMB intensity and polarization power spectra of the 2003 Antarctic flight of the BOOMERANG telescope. The BOOMERANG data alone constrains the parameters of the $\\Lambda$CDM model remarkably well and is consistent with constraints from a multi-experiment combined CMB data set. We add LSS data from the 2dF and SDSS redshift surveys to the combined CMB data set and test several extensions to the standard model including: running of the spectral index, curvature, tensor modes, the effect of massive neutrinos, and an effective equation of state for dark energy. We also include an analysis of constraints to a model which allows a CDM isocurvature admixture.
Testing Tensor-Vector-Scalar Theory with latest cosmological observations
Xu, Xiao-dong; Zhang, Pengjie
2014-01-01
Tensor-Vector-Scalar (TeVeS) is considered as a viable theory of gravity. It produces the Milgrom's modified Newtonian dynamics in the nonrelativistic weak field limit and is free from ghosts. We perform the test of TeVeS theory by confronting to cosmological observations. We find that by including a sterile neutrino, it can mimic $\\Lambda$CDM model and is compatible with Planck data. But there are tensions between Planck and supernova measurements or recent observations of the kinetic Sunyaev-Zel'dovich effect. We observe that the growth rate in TeVeS theory is scale dependent, which can serve as a potential probe in distinguishing it from $\\Lambda$CDM model given future precise observations.
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
Redshift drift in varying speed of light cosmology
Energy Technology Data Exchange (ETDEWEB)
Balcerzak, Adam, E-mail: abalcerz@wmf.univ.szczecin.pl [Institute of Physics, University of Szczecin, Wielkopolska 15, 70-451 Szczecin (Poland); Copernicus Center for Interdisciplinary Studies, Sławkowska 17, 31-016 Kraków (Poland); Dabrowski, Mariusz P., E-mail: mpdabfz@wmf.univ.szczecin.pl [Institute of Physics, University of Szczecin, Wielkopolska 15, 70-451 Szczecin (Poland); Copernicus Center for Interdisciplinary Studies, Sławkowska 17, 31-016 Kraków (Poland)
2014-01-20
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)=c{sub 0}a{sup n}(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{sup −5}, though it will be rather difficult to detect by planned extremely large telescopes (EELT, TMT, GMT) within their accuracy.
Nonlinear growing neutrino cosmology
Ayaita, Youness; Baldi, Marco; Führer, Florian; Puchwein, Ewald; Wetterich, Christof
2016-03-01
The energy scale of dark energy, ˜2 ×10-3 eV , is a long way off compared to all known fundamental scales—except for the neutrino masses. If dark energy is dynamical and couples to neutrinos, this is no longer a coincidence. The time at which dark energy starts to behave as an effective cosmological constant can be linked to the time at which the cosmic neutrinos become nonrelativistic. This naturally places the onset of the Universe's accelerated expansion in recent cosmic history, addressing the why-now problem of dark energy. We show that these mechanisms indeed work in the growing neutrino quintessence model—even if the fully nonlinear structure formation and backreaction are taken into account, which were previously suspected of spoiling the cosmological evolution. The attractive force between neutrinos arising from their coupling to dark energy grows as large as 106 times the gravitational strength. This induces very rapid dynamics of neutrino fluctuations which are nonlinear at redshift z ≈2 . Nevertheless, a nonlinear stabilization phenomenon ensures only mildly nonlinear oscillating neutrino overdensities with a large-scale gravitational potential substantially smaller than that of cold dark matter perturbations. Depending on model parameters, the signals of large-scale neutrino lumps may render the cosmic neutrino background observable.
Ross, Charles H.
2005-04-01
Aristotle thought that the universe was finite and Earth centered. Newton thought that it was infinite. Einstein guessed that the universe was finite, spherical, static, warped, and closed. Hubble's 1930 discovery of the expanding universe, Penzias and Wilson's 1968 discovery of the isotropic CMB, and measurements on light element abundances, however, established a big bang origin. Vera Rubin's 1980 dark matter discovery significantly impacted contending theories. However, 1998 is the year when sufficiently accurate supernova and primordial deuterium data was available to truly explore the universe. CMB anisotropy measurements further extended our cosmological database in 2003. On the theoretical side, Friedmann's 1922 perturbation solution of Einstein's general relativity equations for a static universe has shaped the thought and direction in cosmology for the past 80 years. It describes 3D space as a dynamic function of time. However, 80 years of trying to fit Friedmann's solution to observational data has been a bumpy road - resulting in such counter-intuitive, but necessary, features as rapid inflation, precision tuning, esoteric dark matter, and an accelerating input of esoteric dark energy.
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.
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)
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.
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...
Cosmological test using strong gravitational lensing systems
Yuan, C. C.; Wang, F. Y.
2015-09-01
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 Δτ of images, the velocity dispersion σ of the lensing galaxies and the combination of these two effects, Δτ/σ2. In this paper, in order to carry out one-on-one comparisons between ΛCDM universe and Rh = ct universe, we use a sample containing 36 strong lensing systems with the measurement of velocity dispersion from the Sloan Lens Advanced Camera for Surveys (SLACS) and Lens Structure and Dynamic survey (LSD) survey. Concerning the time-delay effect, 12 two-image lensing systems with Δτ are also used. In addition, Monte Carlo 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 per cent confidence level. Comparing with constraints from Δτ and the velocity dispersion σ, we find that using Δτ/σ2 can improve the discrimination between cosmological models. Despite the independence tests of these methods reveal a correlation between Δτ/σ2 and σ, Δτ/σ2 could be considered as an improved method of σ if more data samples are available.
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...
Cosmological constraints on the Undulant Universe
International Nuclear Information System (INIS)
We use the redshift Hubble parameter H(z) data derived from relative galaxy ages, distant type Ia supernovae (SNe Ia), the Baryonic Acoustic Oscillation (BAO) peak, and the Cosmic Microwave Background (CMB) shift parameter data, to constrain cosmological parameters in the Undulant Universe. We marginalize the likelihood functions over h by integrating the probability density P ∝ e-χ2/2 By using a Markov Chain Monte Carlo (MCMC) technique, we obtain the best fitting results and give the confidence regions in the b - Ωm0 plane. Then we compare their constraints. Our results show that the H(z) data play a similar role with the SNe Ia data in cosmological study. By presenting the independent and joint constraints, we find that the BAO and CMB data play very important roles in breaking the degeneracy compared with the H(z) and SNe Ia data alone. Combined with the BAO or CMB data, one can remarkably improve the constraints. The SNe Ia data sets constrain Ωm0 much tighter than the H(z) data sets, but the H(z) data sets constrain b much tighter than the SNe Ia data sets. All these results show that the Undulant Universe approaches the ΛCDM model. We expect more H(z) data to constrain cosmological parameters in the future. (research papers)
Early Galaxy Formation in Warm Dark Matter Cosmologies
Dayal, Pratika; Mesinger, Andrei; Pacucci, Fabio
2015-06-01
We present a framework for high-redshift (z≳ 7) galaxy formation that traces their dark matter (DM) and baryonic assembly in four cosmologies: cold dark matter (CDM) and warm dark matter (WDM) with particle masses of {{m}x} = 1.5, 3, and 5 keV. We use the same astrophysical parameters regulating star formation and feedback, chosen to match current observations of the evolving ultraviolet luminosity function (UV LF). We find that the assembly of observable (with current and upcoming instruments) galaxies in CDM and {{m}x}≥slant 3 keV WDM results in similar halo mass-to-light ratios (M/L), stellar mass densities (SMDs), and UV LFs. However, the suppression of small-scale structure leads to a notably delayed and subsequently more rapid stellar assembly in the 1.5 keV WDM model. Thus, galaxy assembly in {{m}x}≲ 2 keV WDM cosmologies is characterized by (1) a dearth of small-mass halos hosting faint galaxies and (2) a younger, more UV-bright stellar population, for a given stellar mass. The higher M/L (effect 2) partially compensates for the dearth of small-mass halos (effect 1), making the resulting UV LFs closer to CDM than expected from simple estimates of halo abundances. We find that the redshift evolution of the SMD is a powerful probe of the nature of DM. Integrating down to a limit of {{M}UV}=-16.5 for the James Webb Space Telescope (JWST), the SMD evolves as log (SMD) \\propto -0.63(1+z) in {{m}x}=1.5 keV WDM, as compared to log (SMD) \\propto -0.44(1+z) in CDM. Thus, high-redshift stellar assembly provides a powerful test bed for WDM models, accessible with the upcoming JWST.
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.
International Nuclear Information System (INIS)
We present constraints on cosmological parameters based on a sample of Sunyaev-Zeldovich-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 148GHz. 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 σ8 = 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 σ8 = 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 supernoava which give σ8 = 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.
International Nuclear Information System (INIS)
We present constraints on cosmological parameters based on a sample of Sunyaev-Zel'dovich-selected (SZ-selected) galaxy clusters detected in a millimeter-wave survey by the Atacama Cosmology Telescope. The cluster sample used in this analysis consists of nine optically confirmed high-mass clusters comprising the high-significance end of the total cluster sample identified in 455 deg2 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 four-parameter fit. Marginalizing over the values of the parameters in this fit with conservative priors gives σ8 = 0.851 ± 0.115 and w = -1.14 ± 0.35 for a spatially flat wCDM cosmological model with Wilkinson Microwave Anisotropy Probe (WMAP) seven-year priors on cosmological parameters. This gives a modest improvement in statistical uncertainty over WMAP seven-year constraints alone. Fixing the scaling relation between the cluster mass and SZ signal to a fiducial relation obtained from numerical simulations and calibrated by X-ray observations, we find σ8 = 0.821 ± 0.044 and w = -1.05 ± 0.20. These results are consistent with constraints from WMAP7 plus baryon acoustic oscillations plus Type Ia supernova which give σ8 = 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.
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.
Cosmology with decaying cosmological constant—exact solutions and model testing
Szydłowski, Marek; Stachowski, Aleksander
2015-10-01
We study dynamics of Λ(t) cosmological models which are a natural generalization of the standard cosmological model (the ΛCDM model). We consider a class of models: the ones with a prescribed form of Λ(t)=Λbare+α2/t2. This type of a Λ(t) parametrization is motivated by different cosmological approaches. We interpret the model with running Lambda (Λ(t)) as a special model of an interacting cosmology with the interaction term -dΛ(t)/dt in which energy transfer is between dark matter and dark energy sectors. For the Λ(t) cosmology with a prescribed form of Λ(t) we have found the exact solution in the form of Bessel functions. Our model shows that fractional density of dark energy Ωe is constant and close to zero during the early evolution of the universe. 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-Paczyński test. In this context we formulate a simple criterion of variability of Λ with respect to t in terms of variability of the jerk or sign of estimator (1-Ωm,0-ΩΛ,0). The case study of our model enable us to find an upper limit α2 < 0.012 (2σ C.L.) describing the variation from the cosmological constant while the LCDM model seems to be consistent with various data.
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.
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.
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.
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...
Linking renewable energy CDM projects and TGC schemes: An analysis of different options
International Nuclear Information System (INIS)
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
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.
THE EVOLUTION OF ACTIVE GALACTIC NUCLEI IN WARM DARK MATTER COSMOLOGY
Energy Technology Data Exchange (ETDEWEB)
Menci, N.; Fiore, F.; Lamastra, A. [INAF, Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monteporzio (Italy)
2013-04-01
Recent measurements of the abundance of active galactic nuclei (AGNs) with low luminosities (L{sub 2-10} {<=} 10{sup 44} erg s{sup -1} in the 2-10 keV energy band) at high redshifts (z {>=} 4) provide a serious challenge for cold dark matter (CDM) models based on interaction-driven fueling of AGNs. Using a semi-analytic model of galaxy formation we investigate how such observations fit in a warm dark matter (WDM) scenario of galaxy formation, and compare the results with those obtained in the standard CDM scenario with different efficiencies for the stellar feedback. Taking on our previous exploration of galaxy formation in WDM cosmology, we assume as a reference case a spectrum which is suppressed-compared to the standard CDM case-below a cutoff scale Almost-Equal-To 0.2 Mpc corresponding (for thermal relic WDM particles) to a mass m{sub X} = 0.75 keV. We run our fiducial semi-analytic model with such a WDM spectrum to derive AGN luminosity functions from z Almost-Equal-To 6 to the present over a wide range of luminosities (10{sup 43} {<=} L{sub 2-10}/erg s{sup -1} {<=} 10{sup 46} in the 2-10 keV X-ray band), to compare with recent observations and with the results in the CDM case. When compared with the standard CDM case, the luminosity distributions we obtain assuming a WDM spectrum are characterized by a similar behavior at low redshift, and by a flatter slope at faint magnitudes for z {>=} 3, which provide an excellent fit to present observations. We discuss how such a result compares with CDM models with maximized feedback efficiency, and how future deep AGN surveys will allow for a better discrimination between feedback and cosmological effects on the evolution of AGNs in interaction-driven models for AGN fueling.
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.
Amornwan Resanond; Thanwa Jittsanguan; Damrong Sriphraram
2011-01-01
Ratification to the Kyoto Protocol allows Thailand to voluntarily participate in the Clean Development Mechanism (CDM). CDM not only promotes environmental integrity but also offers business sustainability, which will be then able to enhance company’s competiveness. Due to these enthusiastic impressions, number of CDM registered projects in Thailand has been increased from 5 to 40 projects between 2005 and 2010, respectively. Several business sectors in Thailand have been moving their p...
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
The Age of Precision Cosmology
Chuss, David T.
2012-01-01
In the past two decades, our understanding of the evolution and fate of the universe has increased dramatically. This "Age of Precision Cosmology" has been ushered in by measurements that have both elucidated the details of the Big Bang cosmology and set the direction for future lines of inquiry. Our universe appears to consist of 5% baryonic matter; 23% of the universe's energy content is dark matter which is responsible for the observed structure in the universe; and 72% of the energy density is so-called "dark energy" that is currently accelerating the expansion of the universe. In addition, our universe has been measured to be geometrically flat to 1 %. These observations and related details of the Big Bang paradigm have hinted that the universe underwent an epoch of accelerated expansion known as Uinflation" early in its history. In this talk, I will review the highlights of modern cosmology, focusing on the contributions made by measurements of the cosmic microwave background, the faint afterglow of the Big Bang. I will also describe new instruments designed to measure the polarization of the cosmic microwave background in order to search for evidence of cosmic inflation.
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.
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 ...
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...
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.
Sterile neutrinos with eV masses in cosmology — How disfavoured exactly?
DEFF Research Database (Denmark)
Hamann, Jan; Hannestad, Steen; Raffelt, G.G.;
2011-01-01
sterile neutrinos, then the hot dark matter constraint on the sterile states is considerably relaxed. A further improvement is achieved by allowing a dark energy equation of state parameter w < -1. While BBN strongly disfavours extra radiation beyond the assumed eV-mass sterile neutrino, this constraint...... the minimal ΛCDM model, such sterile neutrinos are strongly disfavoured by current data because they contribute too much hot dark matter. However, if the cosmological framework is extended to include also additional relativistic degrees of freedom beyond the three standard neutrinos and the putative...... can be circumvented by a small νe degeneracy. Any model containing eV-mass sterile neutrinos implies also strong modifications of other cosmological parameters. Notably, the inferred cold dark matter density can shift up by 20-75% relative to the standard ΛCDM value....
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
Energy Ranking Preservation in a N-Body Cosmological Simulation
Dantas, C C; Dantas, Christine C.; Ramos, Fernando M.
2006-01-01
In this paper we present a study of the cosmic flow from the point of view of how clusterings at different dynamical regimes in an expanding universe evolve according to a `coarse-grained' partitioning of their ranked energy distribution. By analysing a Lambda-CDM cosmological simulation from the Virgo Project, we find that cosmic flows evolve in an orderly sense, when tracked from their coarse-grained energy cells, even when nonlinearities are already developed. We show that it is possible to characterize scaling laws for the Pairwise Velocity Distribution in terms of the energy cells, generally valid at the linear and nonlinear clustering regimes.
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
Evolution of star clusters in a cosmological tidal field
Rieder, Steven; Ishiyama, Tomoaki; Langelaan, Paul; Makino, Junichiro; McMillan, Stephen L. W.; Zwart, Simon Portegies
2013-01-01
We present a method to couple N-body star cluster simulations to a cosmological tidal field, using the Astrophysical Multipurpose Software Environment. We apply this method to star clusters embedded in the CosmoGrid dark matter-only LambdaCDM simulation. Our star clusters are born at z = 10 (corresponding to an age of the Universe of about 500 Myr) by selecting a dark matter particle and initializing a star cluster with 32,000 stars on its location. We then follow the dynamical evolution of t...
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
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.
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; 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...
Constraints from the Old Quasar Apm 08279+5255 on Two Classes of $\\Lambda($t$)$-Cosmologies
Jesus, J F
2006-01-01
The viability of two different classes of $\\Lambda(t)$CDM cosmologies is tested by using the APM 08279+5255, an old quasar at redshift $z = 3.91$. In the first class of models, the cosmological term scales as $\\Lambda(t)\\sim R^{-n}$. The particular case $n=0$ describes the standard $\\Lambda$CDM model whereas $n=2$ stands for the Chen and Wu model. For an estimated age of 2 Gyr, it is found that the power has a lower limit $n > 0.21$, whereas for 3 Gyr the limit is $n > 0.6$. Since $n$ can not be so large as $\\sim 0.81$, the $\\Lambda$CDM and Chen and Wu models are also ruled out by this analysis. The second class of models is the one recently proposed by Wang and Meng which describes several $\\Lambda(t)$CDM cosmologies discussed in the literature. By assuming that the true age is 2 Gyr it is found that the $\\epsilon$ parameter satisfies the lower bound $\\epsilon > 0.11$, while for 3 Gyr, a lower limit of $\\epsilon > 0.52$ is obtained. Such limits are slightly modified when the baryonic component is included.
Unifying inflation with ΛCDM epoch in modified f(R) gravity consistent with Solar System tests
International Nuclear Information System (INIS)
We suggest two realistic f(R) and one F(G) modified gravities which are consistent with local tests and cosmological bounds. The typical property of such theories is the presence of the effective cosmological constant epochs in such a way that early-time inflation and late-time cosmic acceleration are naturally unified within single model. It is shown that classical instability does not appear here and Newton law is respected. Some discussion of possible anti-gravity regime appearance and related modification of the theory is done
Unifying inflation with LambdaCDM epoch in modified f(R) gravity consistent with Solar System tests
Nojiri, Shin'ichi; Odintsov, Sergei D.(Department of Physics, Nagoya University, Nagoya 464-8602, Japan)
2007-01-01
We suggest two realistic f(R) and one F(G) modified gravities which are consistent with local tests and cosmological bounds. The typical property of such theories is the presence of the effective cosmological constant epochs in such a way that early-time inflation and late-time cosmic acceleration are naturally unified within single model. It is shown that classical instability does not appear here and Newton law is respected. Some discussion of possible anti-gravity regime appearence and rel...
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...
Kunze, Kerstin E
2016-01-01
Cosmology is becoming an important tool to test particle physics models. We provide an overview of the standard model of cosmology with an emphasis on the observations relevant for testing fundamental physics.
International Nuclear Information System (INIS)
Two Friedman's cosmological papers (1922, 1924) and his own interpretation of the obtained results are briefly reviewed. Discussion follows of Friedman's role in the early development of relativistic cosmology. 18 refs. (author)
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...
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.
Large Scale Cosmological Anomalies and Inhomogeneous Dark Energy
Directory of Open Access Journals (Sweden)
Leandros Perivolaropoulos
2014-01-01
Full Text Available A wide range of large scale observations hint towards possible modifications on the standard cosmological model which is based on a homogeneous and isotropic universe with a small cosmological constant and matter. These observations, also known as “cosmic anomalies” include unexpected Cosmic Microwave Background perturbations on large angular scales, large dipolar peculiar velocity flows of galaxies (“bulk flows”, the measurement of inhomogenous values of the fine structure constant on cosmological scales (“alpha dipole” and other effects. The presence of the observational anomalies could either be a large statistical fluctuation in the context of ΛCDM or it could indicate a non-trivial departure from the cosmological principle on Hubble scales. Such a departure is very much constrained by cosmological observations for matter. For dark energy however there are no significant observational constraints for Hubble scale inhomogeneities. In this brief review I discuss some of the theoretical models that can naturally lead to inhomogeneous dark energy, their observational constraints and their potential to explain the large scale cosmic anomalies.
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
Challenges for Inflationary Cosmology
Brandenberger, Robert H.
2004-01-01
Inflationary cosmology has provided a predictive and phenomenologically very successful scenario for early universe cosmology. Attempts to implement inflation using scalar fields, however, lead to models with serious conceptual problems. I will discuss some of the problems, explain why string theory could provide solutions to a subset of these problems, and give a brief overview of ``string gas cosmology'', one of the approaches to merge string theory and early universe cosmology.
THE ATACAMA COSMOLOGY TELESCOPE: COSMOLOGICAL PARAMETERS FROM THE 2008 POWER SPECTRUM
International Nuclear Information System (INIS)
We present cosmological parameters derived from the angular power spectrum of the cosmic microwave background (CMB) radiation observed at 148 GHz and 218 GHz over 296 deg2 with the Atacama Cosmology Telescope (ACT) during its 2008 season. ACT measures fluctuations at scales 500 3000 = 6.8 ± 2.9 μK2, where Bl≡l(l + 1)Cl/2π. The IR Poisson power at 148 GHz is B3000 = 7.8 ± 0.7 μK2 (Cl = 5.5 ± 0.5 nK2), and a clustered IR component is required with B3000 = 4.6 ± 0.9 μK2, assuming an analytic model for its power spectrum shape. At 218 GHz only about 15% of the power, approximately 27 μK2, is CMB anisotropy at l = 3000. The remaining 85% is attributed to IR sources (approximately 50% Poisson and 35% clustered), with spectral index α = 3.69 ± 0.14 for flux scaling as S(ν)∝να. We estimate primary cosmological parameters from the less contaminated 148 GHz spectrum, marginalizing over SZ and source power. The ΛCDM cosmological model is a good fit to the data (χ2/dof = 29/46), and ΛCDM parameters estimated from ACT+Wilkinson Microwave Anisotropy Probe (WMAP) are consistent with the seven-year WMAP limits, with scale invariant ns = 1 excluded at 99.7% confidence level (CL) (3σ). A model with no CMB lensing is disfavored at 2.8σ. By measuring the third to seventh acoustic peaks, and probing the Silk damping regime, the ACT data improve limits on cosmological parameters that affect the small-scale CMB power. The ACT data combined with WMAP give a 6σ detection of primordial helium, with YP = 0.313 ± 0.044, and a 4σ detection of relativistic species, assumed to be neutrinos, with Neff = 5.3 ± 1.3 (4.6 ± 0.8 with BAO+H0 data). From the CMB alone the running of the spectral index is constrained to be dns /dln k = -0.034 ± 0.018, the limit on the tensor-to-scalar ratio is r -7 (95% CL).
Sato, Masanori; Matsubara, Takahiko
2013-01-01
It is crucial to understand and model a behavior of galaxy biasing for future ambitious galaxy redshift surveys. Using 40 large cosmological N-body simulations for a standard LambdaCDM cosmology, we study the cross-correlation coefficient between matter and the halo density field, which is an indicator of the stochasticity of bias, over a wide redshift range 0\\le z \\le 3. The cross-correlation coefficient is important to extract information on the matter density field, e.g., by combining gala...
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.
Combination and interpretation of observables in Cosmology
Directory of Open Access Journals (Sweden)
Virey Jean-Marc
2010-04-01
Full Text Available The standard cosmological model has deep theoretical foundations but need the introduction of two major unknown components, dark matter and dark energy, to be in agreement with various observations. Dark matter describes a non-relativistic collisionless fluid of (non baryonic matter which amount to 25% of the total density of the universe. Dark energy is a new kind of fluid not of matter type, representing 70% of the total density which should explain the recent acceleration of the expansion of the universe. Alternatively, one can reject this idea of adding one or two new components but argue that the equations used to make the interpretation should be modified consmological scales. Instead of dark matter one can invoke a failure of Newton's laws. Instead of dark energy, two approaches are proposed : general relativity (in term of the Einstein equation should be modified, or the cosmological principle which fixes the metric used for cosmology should be abandonned. One of the main objective of the community is to find the path of the relevant interpretations thanks to the next generation of experiments which should provide large statistics of observationnal data. Unfortunately, cosmological in formations are difficult to pin down directly fromt he measurements, and it is mandatory to combine the various observables to get the cosmological parameters. This is not problematic from the statistical point of view, but assumptions and approximations made for the analysis may bias our interprettion of the data. Consequently, a strong attention should be paied to the statistical methods used to make parameters estimation and for model testing. After a review of the basics of cosmology where the cosmological parameters are introduced, we discuss the various cosmological probes and their associated observables used to extract cosmological informations. We present the results obtained from several statistical analyses combining data of diferent nature but
Disney, M J
2000-01-01
It is argued that some of the recent claims for cosmology are grossly overblown. Cosmology rests on a very small database: it suffers from many fundamental difficulties as a science (if it is a science at all) whilst observations of distant phenomena are difficult to make and harder to interpret. It is suggested that cosmological inferences should be tentatively made and sceptically received.
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.