New model of axion monodromy inflation and its cosmological implications
Energy Technology Data Exchange (ETDEWEB)
Cai, Yi-Fu [CAS Key Laboratory for Researches in Galaxies and Cosmology,Department of Astronomy, University of Science and Technology of China,Chinese Academy of Sciences, Hefei, Anhui 230026 (China); Department of Physics, McGill University,Montréal, QC, H3A 2T8 (Canada); Chen, Fang [Kavli Institute for Theoretical Physics, University of California,Santa Barbara, California 93106 (United States); Ferreira, Elisa G.M.; Quintin, Jerome [Department of Physics, McGill University,Montréal, QC, H3A 2T8 (Canada)
2016-06-10
We propose a new realization of axion monodromy inflation in which axion monodromy arises from torsional cycles in a type IIB compactification. A class of monomial potentials is obtained with specific values for the power index. Moreover, the inflaton mass changes profile due to the couplings between various fields after compactification. Consequently, the potential obtains a step-like profile at some critical scale. We study the cosmological implications of one concrete realization of this model. At the background level, it realizes a sufficiently long inflationary stage, which allows for the violation of the slow-roll conditions for a short period of time when the inflaton is close to the critical scale. Accordingly, the Hubble horizon is perturbed and affects the dynamics of primordial cosmological perturbations. In particular, we analyze the angular power spectrum of B-mode polarization and find a boost on very large scales. We also find that the amplitude of scalar perturbations is suppressed near the critical scale. Thus our model provides an interpretation for the low-ℓ suppression of temperature anisotropies in the CMB power spectrum. We examine these effects and confront the model to observations.
New Cosmological Model and Its Implications on Observational Data Interpretation
Directory of Open Access Journals (Sweden)
Vlahovic Branislav
2013-09-01
Full Text Available The paradigm of ΛCDM cosmology works impressively well and with the concept of inflation it explains the universe after the time of decoupling. However there are still a few concerns; after much effort there is no detection of dark matter and there are significant problems in the theoretical description of dark energy. We will consider a variant of the cosmological spherical shell model, within FRW formalism and will compare it with the standard ΛCDM model. We will show that our new topological model satisfies cosmological principles and is consistent with all observable data, but that it may require new interpretation for some data. Considered will be constraints imposed on the model, as for instance the range for the size and allowed thickness of the shell, by the supernovae luminosity distance and CMB data. In this model propagation of the light is confined along the shell, which has as a consequence that observed CMB originated from one point or a limited space region. It allows to interpret the uniformity of the CMB without inflation scenario. In addition this removes any constraints on the uniformity of the universe at the early stage and opens a possibility that the universe was not uniform and that creation of galaxies and large structures is due to the inhomogeneities that originated in the Big Bang.
Cosmological implications of Geometrothermodynamics
Luongo, Orlando
2013-01-01
We use the formalism of Geometrothermodynamics to derive a series of fundamental equations for thermodynamic systems. It is shown that all these fundamental equations can be used in the context of relativistic cosmology to derive diverse scenarios which include the standard cosmological model, a unified model for dark energy and dark matter, and an effective inflationary model.
Cosmological Implications of Geometrothermodynamics
Luongo, O.; Quevedo, H.
2015-01-01
We use the formalism of Geometrothermodynamics to derive a series of fundamental equations for thermodynamic systems. It is shown that all these fundamental equations can be used in the context of relativistic cosmology to derive diverse scenarios which include the standard cosmological model, a unified model for dark energy and dark matter, and an effective inflationary model.
Terrestrial implications of cosmological gamma-ray burst models
Thorsett, S E
1995-01-01
The observation by the BATSE instrument on the Compton Gamma Ray Observatory that gamma-ray bursts (GRBs) are distributed isotropically around the Earth but nonuniformly in distance has led to the widespread conclusion that GRBs are most likely to be at cosmological distances, making them the most luminous sources known in the Universe. If bursts arise from events that occur in normal galaxies, such as neutron star binary inspirals, then they will also occur in our Galaxy about every hundred thousand to million years. The gamma-ray flux at the Earth due to a Galactic GRB would far exceed that from even the largest solar flares. The absorption of this radiation in the atmosphere would substantially increase the stratospheric nitric oxide concentration through photodissociation of N_2, greatly reducing the ozone concentration for several years through NO_x catalysis, with important biospheric effects due to increased solar ultraviolet flux. A nearby GRB may also leave traces in anomalous radionuclide abundances...
Cosmological implications of Primordial Black Holes
Bernal, Jos\\' e Luis; Bellomo, Nicola; Raccanelli, Alvise; Verde, Licia
2017-01-01
The possibility that a relevant fraction of the dark matter might be comprised of Primordial Black Holes (PBHs) has been seriously reconsidered after LIGO's detection of a $\\sim 30 M_{\\odot}$ binary black holes merger. Despite the strong interest in the model, there is a lack of studies on possible cosmological implications and effects on cosmological parameters inference. We investigate correlations with the other standard cosmological parameters using cosmic microwave background observation...
A closer look at the cosmological implications of the $\\Lambda$HDE model
Wang, Shuang; Zhou, Lanjun; Li, Miao
2016-01-01
In a previous paper, we proposed a heterotic dark energy model, called $\\Lambda$HDE, in which dark energy is composed of two components: cosmological constant (CC) and holographic dark energy (HDE). The aim of present work is to give a more comprehensive and systematic investigation on the cosmological implications of the $\\Lambda$HDE model. Firstly, we make use of the current observations to constrain the $\\Lambda$HDE model, and compare its cosmology-fit results with the results of the $\\Lambda$CDM and the HDE model. Then, by combining a qualitative theoretical analysis with a quantitative numerical study, we discuss the impact of considering curvature on the cosmic evolutions of fractional HDE density $\\Omega_{hde}$ and fractional CC density $\\Omega_{\\Lambda}$, as well as on the ultimate cosmic fate. Finally, we explore the effects of adopting different types of observational data. We find that: (1) the current observational data cannot distinguish the $\\Lambda$HDE model from the $\\Lambda$CDM and the HDE mo...
A closer look at the cosmological implications of the ΛHDE model
Wang, Shuang; Wen, Sixiang; Zhou, Lanjun; Li, Miao
2017-01-01
In a previous paper Hu et al. (2015), we proposed a heterotic dark energy model, called ΛHDE, in which dark energy is composed of two components: cosmological constant (CC) and holographic dark energy (HDE). The aim of this work is to give a more comprehensive and systematic investigation on the cosmological implications of the ΛHDE model. Firstly, we make use of the current observations to constrain the ΛHDE model, and compare its cosmology-fit results with the results of the ΛCDM and the HDE model. Then, by combining a qualitative theoretical analysis with a quantitative numerical study, we discuss the impact of considering curvature on the cosmic evolutions of fractional HDE density Ωhde and fractional CC density ΩΛ, as well as on the ultimate cosmic fate. Finally, we explore the effects of adopting different types of observational data. We find that: (1) the current observational data cannot distinguish the ΛHDE model from the ΛCDM and the HDE model; this indicates that DE may contain multiple components. (2) the asymptotic solution of Ωhde and the corresponding cosmic fate in a flat universe can be extended to the case of a non-flat universe; moreover, compared with the case of a flat universe, considering curvature will make HDE closer to a phantom dark energy. (3) compared with JLA dataset, SNLS3 data more favor a phantom type HDE; in contrast, using other types of observational data have no significant impact on the cosmic evolutions of the ΛHDE model.
Yokoyama, Jun'ichi; Suto, Yasushi
1991-01-01
A phenomenological model to produce isocurvature baryon-number fluctuations is proposed in the framework of inflationary cosmology. The resulting spectrum of density fluctuation is very different from the conventional Harrison-Zel'dovich shape. The model, with the parameters satisfying several requirements from particle physics and cosmology, provides an appropriate initial condition for the minimal baryon isocurvature scenario of galaxy formation discussed by Peebles.
Philosophical Implications of Inflationary Cosmology
Knobe, J; Vilenkin, A; Knobe, Joshua; Olum, Ken D.; Vilenkin, Alexander
2003-01-01
Recent developments in cosmology indicate that every history having a nonzero probability is realized in infinitely many distinct regions of spacetime. Thus, it appears that the universe contains infinitely many civilizations exactly like our own, as well as infinitely many civilizations that differ from our own in any way permitted by physical laws. We explore the implications of this conclusion for ethical theory and for the doomsday argument. In the infinite universe, we find that the doomsday argument applies only to effects which change the average lifetime of all civilizations, and not those which affect our civilization alone.
Cosmological implications of Heisenberg's principle
Gonzalo, Julio A
2015-01-01
The aim of this book is to analyze the all important implications of Heisenberg's Uncertainty Principle for a finite universe with very large mass-energy content such as ours. The earlier and main contributors to the formulation of Quantum Mechanics are briefly reviewed regarding the formulation of Heisenberg's Principle. After discussing “indeterminacy” versus ”uncertainty”, the universal constants of physics are reviewed and Planck's units are given. Next, a novel set of units, Heisenberg–Lemaitre units, are defined in terms of the large finite mass of the universe. With the help of Heisenberg's principle, the time evolution of the finite zero-point energy for the universe is investigated quantitatively. Next, taking advantage of the rigorous solutions of Einstein's cosmological equation for a flat, open and mixed universe of finite mass, the most recent and accurate data on the “age” (to) and the expansion rate (Ho) of the universe and their implications are reconsidered.
Quantum cosmological metroland model
Anderson, E.; Franzen, A.T.
2010-01-01
Relational particle mechanics is useful for modelling whole-universe issues such as quantum cosmology or the problem of time in quantum gravity, including some aspects outside the reach of comparably complex mini-superspace models. In this paper, we consider the mechanics of pure shape and not scale
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.
Tsamis, N. C.; Woodard, R. P.
2016-08-01
We study a class of nonlocal, action-based, and purely gravitational models. These models seek to describe a cosmology in which inflation is driven by a large, bare cosmological constant that is screened by the self-gravitation between the soft gravitons that inflation rips from the vacuum. Inflation ends with the Universe poised on the verge of gravitational collapse, in an oscillating phase of expansion and contraction that should lead to rapid reheating when matter is included. After the attainment of a hot, dense Universe the nonlocal screening terms become constant as the Universe evolves through a conventional phase of radiation domination. The onset of matter domination triggers a much smaller antiscreening effect that could explain the current phase of acceleration.
Energy Technology Data Exchange (ETDEWEB)
Faraggi, A.E.
1996-08-01
Superstring phenomenology aims at achieving two goals. The first is to reproduce the observed physics of the Standard Model. The second is to identify experimental signatures of superstring unification which, if observed, will provide further evidence for the validity of superstring theory. I discuss such potential signatures of superstring unification. I propose that proton lifetime constraints imply that the Standard Model gauge group must be obtained directly at the string level. In this case the unifying gauge group, for example SO(10), is broken to the Standard Model gauge group by ``Wilson lines``. The symmetry breaking by ``Wilson line`` has important implications. It gives rise to exotic massless states which cannot fit into multiplets of the original unifying gauge group. This is an important feature because it results in conservation laws which forbid the interaction of the exotic ``Wilsonian`` states with the Standard Model states. The ``Wilsonian`` matter states then have important phenomenological implications. I discuss two such implications: exotic ``Wilsonian`` states as dark matter candidates and ``Wilsonian`` matter as the messenger sector in gauge mediated dynamical SUSY breaking scenarios.
Implications of a stochastic microscopic Finsler cosmology
Energy Technology Data Exchange (ETDEWEB)
Mavromatos, Nick E. [University of London, Department of Physics, King' s College London, London (United Kingdom); CERN, Theory Division, Geneva 23 (Switzerland); Mitsou, Vasiliki A. [CSIC - Universitat de Valencia, Instituto de Fisica Corpuscular (IFIC), Valencia (Spain); Sarkar, Sarben; Vergou, Ariadne [University of London, Department of Physics, King' s College London, London (United Kingdom)
2012-03-15
Within the context of supersymmetric space-time (D-particle) foam in string/brane-theory, we discuss a Finsler-induced cosmology and its implications for (thermal) dark matter abundances. This constitutes a truly microscopic model of dynamical space-time, where Finsler geometries arise naturally. The D-particle foam model involves point-like brane defects (D-particles), which provide the topologically non-trivial foamy structures of space-time. The D-particles can capture and emit stringy matter and this leads to a recoil of D-particles. It is indicated how one effect of such a recoil of D-particles is a back-reaction on the space-time metric of Finsler type which is stochastic. We show that such a type of stochastic space-time foam can lead to acceptable cosmologies at late epochs of the Universe, due to the non-trivial properties of the supersymmetric (BPS like) D-particle defects, which are such so as not to affect significantly the Hubble expansion. The restrictions placed on the free parameters of the Finsler type metric are obtained from solving the Boltzmann equation in this background for relic abundances of a Lightest Supersymmetric Particle (LSP) dark matter candidate. It is demonstrated that the D-foam acts as a source for particle production in the Boltzmann equation, thereby leading to enhanced thermal LSP relic abundances relative to those in the Standard {lambda}CDM cosmology. For D-particle masses of order TeV, such effects may be relevant for dark matter searches at colliders. The latter constraints complement those coming from high-energy gamma-ray astronomy on the induced vacuum refractive index that D-foam models entail. We also comment briefly on the production mechanisms of such TeV-mass stringy defects at colliders, which, in view of the current LHC experimental searches, will impose further constraints on their couplings. (orig.)
LHC signatures and cosmological implications of the E6 inspired SUSY models
Nevzorov, R
2015-01-01
The phenomenological implications of the E6 inspired supersymmetric models based on the Standard Model gauge group together with extra U(1)_N gauge symmetry under which right-handed neutrinos have zero charge are examined. In these models single discrete symmetry forbids the tree-level flavour changing processes and the most dangerous operators that violate baryon and lepton numbers. The two-loop renormalisation group flow of the gauge and Yukawa couplings is explored and the qualitative pattern of the Higgs spectrum in the case of the quasi-fixed point scenario is discussed. These E6 inspired models contain two dark-matter candidates. The presence of exotic states in these models gives rise to the nonstandard decays of the lightest Higgs boson which are also considered.
The Standard Cosmological Model
Scott, D
2005-01-01
The Standard Model of Particle Physics (SMPP) is an enormously successful description of high energy physics, driving ever more precise measurements to find "physics beyond the standard model", as well as providing motivation for developing more fundamental ideas that might explain the values of its parameters. Simultaneously, a description of the entire 3-dimensional structure of the present-day Universe is being built up painstakingly. Most of the structure is stochastic in nature, being merely the result of the particular realisation of the "initial conditions" within our observable Universe patch. However, governing this structure is the Standard Model of Cosmology (SMC), which appears to require only about a dozen parameters. Cosmologists are now determining the values of these quantities with increasing precision in order to search for "physics beyond the standard model", as well as trying to develop an understanding of the more fundamental ideas which might explain the values of its parameters. Althoug...
FLRW viscous cosmological models
Khadekar, G S; Meng, X -H
2016-01-01
In this paper we solve Friedmann equations by considering a universal media as a non-perfect fluid with bulk viscosity and is described by a general "gamma law" equation of state of the form $p= (\\gamma -1) \\rho + \\Lambda(t)$, where the adiabatic parameter $\\gamma$ varies with scale factor $R$ of the metric and $\\Lambda$ is the time dependent cosmological constant. A unified description of the early evolution of the universe is presented by assuming the bulk viscosity and cosmological parameter in a linear combination of two terms of the form: $\\Lambda(t)=\\Lambda_{0} + \\Lambda_{1}\\frac{\\dot{R}}{R}$ and $\\zeta = \\zeta_{0} + \\zeta_{1} \\frac{\\dot{R}}{R}$, where $\\Lambda_{0},\\;\\Lambda_{1},\\, \\zeta_{0}$ and $ \\zeta_{1}$ are constants, in which an inflationary phase is followed by the radiation dominated phase. For this general gamma law equation of state, an entirely integrable dynamical equation to the scale factor $R$ is obtained along with its exact solutions. In this framework we demonstrate that the model can...
Bimetric gravity doubly coupled to matter: theory and cosmological implications
Energy Technology Data Exchange (ETDEWEB)
Akrami, Yashar; Koivisto, Tomi S.; Mota, David F.; Sandstad, Marit, E-mail: yashar.akrami@astro.uio.no, E-mail: t.s.koivisto@astro.uio.no, E-mail: d.f.mota@astro.uio.no, E-mail: marit.sandstad@astro.uio.no [Institute of Theoretical Astrophysics, University of Oslo P.O. Box 1029 Blindern, N-0315 Oslo (Norway)
2013-10-01
A ghost-free theory of gravity with two dynamical metrics both coupled to matter is shown to be consistent and viable. Its cosmological implications are studied, and the models, in particular in the context of partially massless gravity, are found to explain the cosmic acceleration without resorting to dark energy.
Quantum cosmological metroland model
Energy Technology Data Exchange (ETDEWEB)
Anderson, Edward [DAMTP, Cambridge (United Kingdom); Franzen, Anne, E-mail: ea212@cam.ac.u, E-mail: a.t.franzen@uu.n [Spinoza Institute, Utrecht (Netherlands)
2010-02-21
Relational particle mechanics is useful for modelling whole-universe issues such as quantum cosmology or the problem of time in quantum gravity, including some aspects outside the reach of comparably complex mini-superspace models. In this paper, we consider the mechanics of pure shape and not scale of four particles on a line, so that the only physically significant quantities are ratios of relative separations between the constituents' physical objects. Many of our ideas and workings extend to the N-particle case. As such models' configurations resemble depictions of metro lines in public transport maps, we term them 'N-stop metrolands'. This 4-stop model's configuration space is a 2-sphere, from which our metroland mechanics interpretation is via the 'cubic' tessellation. This model yields conserved quantities which are mathematically SO(3) objects like angular momenta but are physically relative dilational momenta (i.e. coordinates dotted with momenta). We provide and interpret various exact and approximate classical and quantum solutions for 4-stop metroland; from these results one can construct expectations and spreads of shape operators that admit interpretations as relative sizes and the 'homogeneity of the model universe's contents', and also objects of significance for the problem of time in quantum gravity (e.g. in the naive Schroedinger and records theory timeless approaches).
Cosmological and astrophysical implications of sterile neutrinos
Petraki, Kalliopi
The discovery of neutrino masses suggests that the Standard Model should be supplemented with new gauge-singlet fermions, often called sterile neutrinos. The interplay among the new couplings introduced in the Standard Model can accommodate the neutrino oscillation data for a variety of choices: the new particles can be extremely heavy and practically unobservable, or they can be light, in which case they can solve several long-standing puzzles. It has been shown, for example, that sterile neutrinos in some range of masses can account for dark matter, their emission from a supernova can explain pulsar kicks, arid their decays can play an important role in the formation of the first stars. Though indirect, these clues indicate that sterile neutrinos can be the minimal solution to a variety of unsolved problems. This emphasizes the importance of investigating further the consequences of these new degrees of freedom for cosmology and astrophysics. In this dissertation, I explore the possible role of sterile neutrinos of different mass scales in some cosmological and astrophysical phenomena. A minimal extension of the Higgs sector of the Standard Model, with a gauge- singlet boson coupled to sterile neutrinos, can provide a consistent framework for the theory of neutrino masses, and can produce a relic population of keV sterile neutrinos via decays of the singlet Higgs. The latter can account for the dark matter of the universe. The mechanism operates around the electroweak scale, and has interesting consequences for the electroweak phase transition. Relic sterile neutrinos produced via decays at the electroweak scale constitute colder dark matter than those produced via other previously suggested mechanisms. The primordial thermal content of dark matter has important implications for the formation of cosmic structures, such as clusters and galaxies. The assessment of the relevant properties suggests that sterile neutrinos produced at the electroweak scale are a
The Maxwell-Chern-Simons gravity, and its cosmological implications
Haghani, Zahra; Harko, Tiberiu; Shahidi, Shahab
2017-08-01
We consider the cosmological implications of a gravitational theory containing two vector fields coupled via a generalized Chern-Simons term. One of the vector fields is the usual Maxwell field, while the other is a constrained vector field with constant norm included in the action via a Lagrange multiplier. The theory admits a de Sitter type solution, with healthy cosmological perturbations. We also show that there are seven degrees of freedom that propagate on top of de Sitter space-time, consisting of two tensor polarizations, four degrees of freedom related to the two vector fields, and a scalar degree of freedom that makes one of the vector fields massive. We investigate the cosmological evolution of Bianchi type I space-time, by assuming that the matter content of the Universe can be described by the stiff and dust. The cosmological evolution of the Bianchi type I Universe strongly depends on the initial conditions of the physical quantities, as well as on the model parameters. The mean anisotropy parameter, and the deceleration parameter, are also studied, and we show that independently of the matter equation of state the cosmological evolution of the Bianchi type I Universe always ends in an isotropic de Sitter type phase.
Matrix Model Approach to Cosmology
Chaney, A; Stern, A
2015-01-01
We perform a systematic search for rotationally invariant cosmological solutions to matrix models, or more specifically the bosonic sector of Lorentzian IKKT-type matrix models, in dimensions $d$ less than ten, specifically $d=3$ and $d=5$. After taking a continuum (or commutative) limit they yield $d-1$ dimensional space-time surfaces, with an attached Poisson structure, which can be associated with closed, open or static cosmologies. For $d=3$, we obtain recursion relations from which it is possible to generate rotationally invariant matrix solutions which yield open universes in the continuum limit. Specific examples of matrix solutions have also been found which are associated with closed and static two-dimensional space-times in the continuum limit. The solutions provide for a matrix resolution of cosmological singularities. The commutative limit reveals other desirable features, such as a solution describing a smooth transition from an initial inflation to a noninflationary era. Many of the $d=3$ soluti...
Cosmological implications of the Machian principle.
Fahr, Hans J; Zoennchen, Jochen H
2006-12-01
The famous idea of Ernst Mach concerning the non-absolute but relational character of particle inertia is taken up in this paper and is reinvestigated with respect to its cosmological implications. From Thirring's general relativistic study of the old Newtonian problem of the relativity of rotations in different reference systems, it appears that the equivalence principle with respect to rotating reference systems, if at all, can only be extended to the system of the whole universe, if the mass of the universe scales with the effective radius or extent of the universe. A reanalysis of Thirring's derivations still reveals this astonishing result, and thus the general question must be posed: how serious this result has to be taken with respect to cosmological implications. As we will show, the equivalence principle is, in fact, fulfilled by a universe with vanishing curvature, i.e. with a curvature parameter k = 0, which just has the critical density rho (crit) = (3H)(2)/8piG, where H is the Hubble constant. It turns out, however, that this principle can only permanently be fulfilled in an evolving cosmos, if the cosmic mass density, different from its conventional behaviour, varies with the reciprocal of the squared cosmic scale. This, in fact, would automatically be realized, if the mass of each cosmic particle scales with the scale of the universe. The latter fact, on one hand, is a field-theoretical request from a general relativistic field theory which fulfills H. Weyl's requirement of a conformal scale invariance. On the other hand, it can perhaps also be concluded on purely physical grounds, when taking into account that as source of the cosmic metrics only an effective mass density can be taken. This mass density represents the bare mass density reduced by its mass equivalent of gravitational self-binding energy. Some interesting cosmological conclusions connected with this fact are pointed out in this paper.
Cosmological implications of modified gravity induced by quantum metric fluctuations
Liu, Xing; Liang, Shi-Dong
2016-01-01
We investigate the cosmological implications of modified gravities induced by the quantum fluctuations of the gravitational metric. If the metric can be decomposed as the sum of the classical and of a fluctuating part, of quantum origin, then the corresponding Einstein quantum gravity generates at the classical level modified gravity models with a nonminimal coupling between geometry and matter. As a first step in our study, after assuming that the expectation value of the quantum correction can be generally expressed in terms of an arbitrary second order tensor constructed from the metric and from the thermodynamic quantities characterizing the matter content of the Universe, we derive the (classical) gravitational field equations in their general form. We analyze in detail the cosmological models obtained by assuming that the quantum correction tensor is given by the coupling of a scalar field and of a scalar function to the metric tensor, and by a term proportional to the matter energy-momentum tensor. For...
Cosmological implications of Higgs field fluctuations during inflation
Grobov, A V; Rubin, S G
2016-01-01
Cosmological implications of Higgs field fluctuations during inflation are considered. This study is based on the Standard Model and the standard quadratic model of chaotic inflation where the Higgs field is minimally coupled to gravity and has no direct coupling to the inflaton. In the Standard model the renormalisation group improved effective potential develops an instability (an additional minimum and maximum) at large field values. It is shown that such a new maximum should take place at an energy scale above $10^{14} \\;\\text{GeV},$ otherwise a universe like ours is extremely unlikely. The extension to the case of the Higgs field interacting with the inflaton field is discussed.
Cosmological models of galaxy formation
Menci, N.
I review the present status of galaxy formation models within a cosmological framework. I focus on semi-analytic models based on the Cold Dark Matter scenario, discussing the role of the different physical process involving dark matter and baryons in determining the observed statistical properties of galaxies and their dependence on cosmic time and on environment evolution. I will highlight some present problems and briefly present the main effects of assuming a Warm Dark Matter scenario.
Cosmological implications of modified gravity induced by quantum metric fluctuations
Energy Technology Data Exchange (ETDEWEB)
Liu, Xing [Sun Yat-Sen University, School of Physics, Guangzhou (China); Sun Yat-Sen University, Yat Sen School, Guangzhou (China); Harko, Tiberiu [Babes-Bolyai University, Department of Physics, Cluj-Napoca (Romania); University College London, Department of Mathematics, London (United Kingdom); Liang, Shi-Dong [Sun Yat-Sen University, School of Physics, Guangzhou (China); Sun Yat-Sen University, State Key Laboratory of Optoelectronic Material and Technology, Guangdong Province Key Laboratory of Display Material and Technology, School of Physics, Guangzhou (China)
2016-08-15
We investigate the cosmological implications of modified gravities induced by the quantum fluctuations of the gravitational metric. If the metric can be decomposed as the sum of the classical and of a fluctuating part, of quantum origin, then the corresponding Einstein quantum gravity generates at the classical level modified gravity models with a non-minimal coupling between geometry and matter. As a first step in our study, after assuming that the expectation value of the quantum correction can be generally expressed in terms of an arbitrary second order tensor constructed from the metric and from the thermodynamic quantities characterizing the matter content of the Universe, we derive the (classical) gravitational field equations in their general form. We analyze in detail the cosmological models obtained by assuming that the quantum correction tensor is given by the coupling of a scalar field and of a scalar function to the metric tensor, and by a term proportional to the matter energy-momentum tensor. For each considered model we obtain the gravitational field equations, and the generalized Friedmann equations for the case of a flat homogeneous and isotropic geometry. In some of these models the divergence of the matter energy-momentum tensor is non-zero, indicating a process of matter creation, which corresponds to an irreversible energy flow from the gravitational field to the matter fluid, and which is direct consequence of the non-minimal curvature-matter coupling. The cosmological evolution equations of these modified gravity models induced by the quantum fluctuations of the metric are investigated in detail by using both analytical and numerical methods, and it is shown that a large variety of cosmological models can be constructed, which, depending on the numerical values of the model parameters, can exhibit both accelerating and decelerating behaviors. (orig.)
Cosmological implications of modified gravity induced by quantum metric fluctuations
Liu, Xing; Harko, Tiberiu; Liang, Shi-Dong
2016-08-01
We investigate the cosmological implications of modified gravities induced by the quantum fluctuations of the gravitational metric. If the metric can be decomposed as the sum of the classical and of a fluctuating part, of quantum origin, then the corresponding Einstein quantum gravity generates at the classical level modified gravity models with a non-minimal coupling between geometry and matter. As a first step in our study, after assuming that the expectation value of the quantum correction can be generally expressed in terms of an arbitrary second order tensor constructed from the metric and from the thermodynamic quantities characterizing the matter content of the Universe, we derive the (classical) gravitational field equations in their general form. We analyze in detail the cosmological models obtained by assuming that the quantum correction tensor is given by the coupling of a scalar field and of a scalar function to the metric tensor, and by a term proportional to the matter energy-momentum tensor. For each considered model we obtain the gravitational field equations, and the generalized Friedmann equations for the case of a flat homogeneous and isotropic geometry. In some of these models the divergence of the matter energy-momentum tensor is non-zero, indicating a process of matter creation, which corresponds to an irreversible energy flow from the gravitational field to the matter fluid, and which is direct consequence of the non-minimal curvature-matter coupling. The cosmological evolution equations of these modified gravity models induced by the quantum fluctuations of the metric are investigated in detail by using both analytical and numerical methods, and it is shown that a large variety of cosmological models can be constructed, which, depending on the numerical values of the model parameters, can exhibit both accelerating and decelerating behaviors.
Early Modified Gravity: Implications for Cosmology
Brax, Philippe; Clesse, Sebastien; Davis, Anne-Christine; Sculthorpe, Gregory
2013-01-01
We study the effects of modifications of gravity after Big Bang Nucleosynthesis (BBN) which would manifest themselves mainly before recombination. We consider their effects on the Cosmic Microwave Background (CMB) radiation and on the formation of large scale structure. The models that we introduce here represent all screened modifications of General Relativity (GR) which evade the local tests of gravity such as the violation of the strong equivalence principle as constrained by the Lunar Ranging experiment. We use the tomographic description of modified gravity which defines models with screening mechanisms of the chameleon or Damour-Polyakov types and allows one to relate the temporal evolution of the mass and the coupling to matter of a scalar field to its Lagrangian and also to cosmological perturbations. The models with early modifications of gravity all involve a coupling to matter which is stronger in the past leading to effects on perturbations before recombination while minimising deviations from Lam...
Post-Newtonian cosmological models
Sanghai, Viraj A A
2015-01-01
We construct a framework to probe the effect of non-linear structure formation on the large-scale expansion of the universe. We take a bottom-up approach to cosmological modelling by splitting our universe into cells. The matter content within each cell is described by the post-Newtonian formalism. We assume that most of the cell is in the vicinity of weak gravitational fields, so that it can be described using a perturbed Minkowski metric. Our cells are patched together using the Israel junction conditions. We impose reflection symmetry across the boundary of these cells. This allows us to calculate the equation of motion for the boundary of the cell and, hence, the expansion rate of the universe. At Newtonian order, we recover the standard Friedmann-like equations. At post-Newtonian orders, we obtain a correction to the large-scale expansion of the universe. Our framework does not depend on the process of averaging in cosmology. As an example, we use this framework to investigate the cosmological evolution ...
Cosmological implications of different baryon acoustic oscillation data
Wang, Shuang; Hu, YaZhou; Li, Miao
2017-04-01
In this work, we explore the cosmological implications of different baryon acoustic oscillation (BAO) data, including the BAO data extracted by using the spherically averaged one-dimensional galaxy clustering (GC) statistics (hereafter BAO1) and the BAO data obtained by using the anisotropic two-dimensional GC statistics (hereafter BAO2). To make a comparison, we also take into account the case without BAO data (hereafter NO BAO). Firstly, making use of these BAO data, as well as the SNLS3 type Ia supernovae sample and the Planck distance priors data, we give the cosmological constraints of the ΛCDM, the wCDM, and the Chevallier-Polarski-Linder (CPL) model. Then, we discuss the impacts of different BAO data on cosmological consquences, including its effects on parameter space, equation of state (EoS), figure of merit (FoM), deceleration-acceleration transition redshift, Hubble parameter H( z), deceleration parameter q( z), statefinder hierarchy S 3 (1)( z), S 4 (1)( z) and cosmic age t( z). We find that: (1) NO BAO data always give a smallest fractional matter density Ω m0, a largest fractional curvature density Ωk0 and a largest Hubble constant h; in contrast, BAO1 data always give a largest Ω m0, a smallest Ω k0 and a smallest h. (2) For the wCDM and the CPL model, NO BAO data always give a largest EoS w; in contrast, BAO2 data always give a smallest w. (3) Compared with the case of BAO1, BAO2 data always give a slightly larger FoM, and thus can give a cosmological constraint with a slightly better accuracy. (4) The impacts of different BAO data on the cosmic evolution and the comic age are very small, and cannot be distinguished by using various dark energy diagnoses and the cosmic age data.
Cosmological implications of different baryon acoustic oscillation data
Wang, Shuang; Hu, YaZhou; Li, Miao
2017-04-01
In this work, we explore the cosmological implications of different baryon acoustic oscillation (BAO) data, including the BAO data extracted by using the spherically averaged one-dimensional galaxy clustering (GC) statistics (hereafter BAO1) and the BAO data obtained by using the anisotropic two-dimensional GC statistics (hereafter BAO2). To make a comparison, we also take into account the case without BAO data (hereafter NO BAO). Firstly, making use of these BAO data, as well as the SNLS3 type Ia supernovae sample and the Planck distance priors data, we give the cosmological constraints of the ΛCDM, the wCDM, and the Chevallier-Polarski-Linder (CPL) model. Then, we discuss the impacts of different BAO data on cosmological consquences, including its effects on parameter space, equation of state (EoS), figure of merit (FoM), deceleration-acceleration transition redshift, Hubble parameter H( z), deceleration parameter q( z), statefinder hierarchy S 3 (1)( z), S 4 (1)( z) and cosmic age t( z). We find that: (1) NO BAO data always give a smallest fractional matter density Ω m0, a largest fractional curvature density Ωk0 and a largest Hubble constant h; in contrast, BAO1 data always give a largest Ω m0, a smallest Ω k0 and a smallest h. (2) For the wCDM and the CPL model, NO BAO data always give a largest EoS w; in contrast, BAO2 data always give a smallest w. (3) Compared with the case of BAO1, BAO2 data always give a slightly larger FoM, and thus can give a cosmological constraint with a slightly better accuracy. (4) The impacts of different BAO data on the cosmic evolution and the comic age are very small, and cannot be distinguished by using various dark energy diagnoses and the cosmic age data.
Plane symmetric cosmological models
Yadav, Anil Kumar; Ray, Saibal; Mallick, A
2016-01-01
In this work, we perform the Lie symmetry analysis on the Einstein-Maxwell field equations in plane symmetric spacetime. Here Lie point symmetries and optimal system of one dimensional subalgebras are determined. The similarity reductions and exact solutions are obtained in connection to the evolution of universe. The present study deals with the electromagnetic energy of inhomogeneous universe where $F_{12}$ is the non-vanishing component of electromagnetic field tensor. To get a deterministic solution, it is assumed that the free gravitational field is Petrov type-II non-degenerate. The electromagnetic field tensor $F_{12}$ is found to be positive and increasing function of time. As a special case, to validate the solution set, we discuss some physical and geometric properties of a specific sub-model.
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.
Magnetic monopoles and relativistic cosmological models
Energy Technology Data Exchange (ETDEWEB)
Stein-Schabes, J.A.
1984-01-01
A dissertation is presented on magnetic monopoles and relativistic cosmological models. The maximum number density of monopoles in various astrophysical scenarios was investigated along with: the monopole flux in the galaxy, the allowed monopole abundance, and the formation of stable monopole orbits. Limits on the mass and lifetime of monopolonium were calculated. Boltzmann's equation was used to calculate the monopole abundance in a magnetic axisymmetric Bianchi I cosmological model, and a solution was found describing an axisymmetric Bianchi I magnetic cosmology with monopoles. New inhomogeneous solutions to Einstein's equations were found. Finally, stability and inflation in Kaluza-Klein cosmologies in d + D + 1 dimensions was studied.
Cosmological model with dynamical curvature
Stichel, Peter C
2016-01-01
We generalize the recently introduced relativistic Lagrangian darkon fluid model (EPJ C (2015) 75:9) by starting with a self-gravitating geodesic fluid whose energy-momentum tensor is dust-like with a nontrivial energy flow. The corresponding covariant propagation and constraint equations are considered in a shear-free nonrelativistic limit whose analytic solutions determine the 1st-order relativistic correction to the spatial curvature. This leads to a cosmological model where the accelerated expansion of the Universe is driven by a time-dependent spatial curvature without the need for introducing any kind of dark energy. We derive the differential equation to be satisfied by the area distance for this model.
Gravitational particle production in oscillating backgrounds and its cosmological implications
Ema, Yohei; Jinno, Ryusuke; Mukaida, Kyohei; Nakayama, Kazunori
2016-09-01
We study the production of light particles due to the oscillation of the Hubble parameter or the scale factor. Any coherently oscillating scalar field, irrespective of its energy fraction in the Universe, imprints such an oscillating feature on them. Not only Einstein gravity but the extended gravity models, such as models with nonminimal (derivative) coupling to gravity and f (R ) gravity, lead to oscillation of the scale factor. We present a convenient way to estimate the gravitational particle production rate in these circumstances. Cosmological implications of gravitational particle production, such as dark matter/radiation and moduli problem, are discussed. For example, if the theory is described solely by the standard model plus the Peccei-Quinn sector, the Starobinsky R2 inflation may lead to an observable amount of axion dark radiation.
Gravitational Particle Production in Oscillating Background and Its Cosmological Implications
Ema, Yohei; Mukaida, Kyohei; Nakayama, Kazunori
2016-01-01
We study production of light particles due to oscillation of the Hubble parameter or the scale factor. Any coherently oscillating scalar field, irrespective of its energy fraction in the universe, imprints such an oscillating feature on them. Not only the Einstein gravity but extended gravity models, such as models with non-minimal (derivative) coupling to gravity and $f(R)$ gravity, lead to oscillation of the scale factor. We present a convenient way to estimate the gravitational particle production rate in these circumstances. Cosmological implications of gravitational particle production, such as dark matter/radiation and moduli problem, are discussed. For example, if the theory is described solely by the standard model plus the Peccei-Quinn sector, the Starobinsky $R^2$ inflation may lead to observable amount of axion dark radiation.
FIRBACK Source Counts and Cosmological Implications
Dole, H; Lagache, G; Puget, J L; Aussel, H; Bouchet, F R; Ciliegi, P; Clements, D L; Césarsky, C J; Désert, F X; Elbaz, D; Franceschini, A; Guiderdoni, B; Harwit, M; Laureijs, R J; Lemke, D; McMahon, R; Moorwood, A F M; Oliver, S; Reach, W T; Rowan-Robinson, M; Stickel, M; Dole, Herve; Gispert, Richard; Lagache, Guilaine; Puget, Jean-Loup
2000-01-01
FIRBACK is a one of the deepest surveys performed at 170 microns with ISOPHOTonboard ISO, and is aimed at the study of cosmic far infrared backgroundsources. About 300 galaxies are detected in an area of four square degrees, andsource counts present a strong slope of 2.2 on an integral "logN-logS" plot,which cannot be due to cosmological evolution if no K-correction is present.The resolved sources account for less than 100f the Cosmic InfraredBackground at 170 microns. In order to understand the nature of the sourcescontributing to the CIB, and to explain deep source counts at otherwavelengths, we have developed a phenomenological model, which constrains in asimple way the luminosity function evolution with redshift, and fits all theexisting deep source counts from the mid-infrared to the submillimetre range.Images, materials and papers available on the FIRBACK web:http://wwwfirback.ias.u-psud.fr wwwfirback.ias.u-psud.fr
BRS structure of simple model of cosmological constant and cosmology
Mori, Taisaku; Nitta, Daisuke; Nojiri, Shin'ichi
2017-07-01
In Mod. Phys. Lett. A 31, 1650213 (2016, 10.1142/S0217732316502138), Nojiri proposed a simple model in order to solve one of the problems related to the cosmological constant. The model is induced from a topological field theory, and the model has an infinite number of BRS symmetries. The BRS symmetries are, in general, spontaneously broken, however. We investigate the BRS symmetry in detail and show that there is one and only one BRS symmetry which is not broken, and the unitarity can be guaranteed. In the model, the quantum problem of the vacuum energy, which may be identified with the cosmological constant, reduces to the classical problem of the initial condition. We investigate the cosmology given by the model and specify the region of the initial conditions, which could be consistent with the evolution of the Universe. We also show that there is a stable solution describing the de Sitter space-time, which may explain the accelerating expansion in the current Universe.
Supersymmetric quantum cosmology for Bianchi class A models
Macías, A; Socorro, J; Macías, Alfredo; Mielke, Eckehard W.; Socorro, José
1998-01-01
The canonical theory of (N=1) supergravity, with a matrix representation for the gravitino covector-spinor, is applied to the Bianchi class A spatially homogeneous cosmologies. The full Lorentz constraint and its implications for the wave function of the universe are analyzed in detail. We found that in this model no physical states other than the trivial "rest frame" type occur.
Will Quantum Cosmology Resurrect Chaotic Inflation Model?
Kim, Sang Pyo; Kim, Won
2016-07-01
The single field chaotic inflation model with a monomial power greater than one seems to be ruled out by the recent Planck and WMAP CMB data while Starobinsky model with a higher curvature term seems to be a viable model. Higher curvature terms being originated from quantum fluctuations, we revisit the quantum cosmology of the Wheeler-DeWitt equation for the chaotic inflation model. The semiclassical cosmology emerges from quantum cosmology with fluctuations of spacetimes and matter when the wave function is peaked around the semiclassical trajectory with quantum corrections a la the de Broglie-Bohm pilot theory.
Will quantum cosmology resurrect chaotic inflation model?
Kim, Sang Pyo
2016-01-01
The single field chaotic inflation model with a monomial power greater than one seems to be ruled out by the recent Planck and WMAP CMB data while Starobinsky model with a higher curvature term seems to be a viable model. Higher curvature terms being originated from quantum fluctuations, we revisit the quantum cosmology of the Wheeler-DeWitt equation for the chaotic inflation model. The semiclassical cosmology emerges from quantum cosmology with fluctuations of spacetimes and matter when the wave function is peaked around the semiclassical trajectory with quantum corrections a la the de Broglie-Bohm pilot theory.
Astrophysical and Cosmological Implications of Large Volume String Compactifications
Conlon, Joseph P
2007-01-01
We study the spectrum, couplings and cosmological and astrophysical implications of the moduli fields for the class of Calabi-Yau IIB string compactifications for which moduli stabilisation leads to an exponentially large volume V ~ 10^{15} l_s^6 and an intermediate string scale m_s ~ 10^{11}GeV, with TeV-scale observable supersymmetry breaking. All K\\"ahler moduli except for the overall volume are heavier than the susy breaking scale, with m ~ ln(M_P/m_{3/2}) m_{3/2} ~ (\\ln(M_P/m_{3/2}))^2 m_{susy} ~ 500 TeV and, contrary to standard expectations, have matter couplings suppressed only by the string scale rather than the Planck scale. These decay to matter early in the history of the universe, with a reheat temperature T ~ 10^7 GeV, and are free from the cosmological moduli problem (CMP). The heavy moduli have a branching ratio to gravitino pairs of 10^{-30} and do not suffer from the gravitino overproduction problem. The overall volume modulus is a distinctive feature of these models and is an M_{planck}-cou...
Cosmological Implications of the Effective Field Theory of Cosmic Acceleration
Mueller, Eva-Maria; Watson, Scott
2012-01-01
We consider cosmological constraints arising from the background expansion history on the ef- fective field theory of cosmic acceleration, a theoretical framework that allows for a unified way to classify both models of dark energy and modified gravity within the linear regime. In the Einstein frame, the most general action for the background can be written in terms of a canonical scalar field which is non-minimally coupled to matter. The leading corrections to the action are expressible through a quartic kinetic term, and scalar couplings to a Gauss-Bonnet curvature term and the Einstein tensor. We determine the implications of the terms in this general action for the predicted expansion history in the context of dynamical attractors. We find that each modifies the matter dominated and/or accelerative eras in ways that allow us to place cosmological constraints on them. We present current constraints on the effective action using the latest Type Ia supernovae, Cosmic Microwave Background, and Baryonic Acoust...
Current Status of cosmological models with mixed dark matter
Mikheeva, E V
2000-01-01
An analysis of cosmological mixed dark matter models in spatially flat Friedmann Universe with zero $\\Lambda$-term is presented. We argue that the introduction of cosmic gravity waves helps to satisfy observational constraints. The analysis of models is based on the confrontation with the mass function of clusters of galaxies and the CMB anisotropy. The implication of Press-Schechter formalism allowed to constrain $\\sigma_8=0.52 \\pm 0.01$. This normalisation of the spectrum of density perturbations has been used to calculate numerically the value of the large scale CMB anisotropy and the relative contribution of cosmological gravitational waves, T/S. We found that increasing $\\Omega_\
Isotropic cosmological singularities other matter models
Tod, K P
2003-01-01
Isotropic cosmological singularities are singularities which can be removed by rescaling the metric. In some cases already studied (gr-qc/9903008, gr-qc/9903009, gr-qc/9903018) existence and uniqueness of cosmological models with data at the singularity has been established. These were cosmologies with, as source, either perfect fluids with linear equations of state or massless, collisionless particles. In this article we consider how to extend these results to a variety of other matter models. These are scalar fields, massive collisionless matter, the Yang-Mills plasma of Choquet-Bruhat, or matter satisfying the Einstein-Boltzmann equation.
Vittorio, Nicola
2017-01-01
Modern cosmology has changed significantly over the years, from the discovery to the precision measurement era. The data now available provide a wealth of information, mostly consistent with a model where dark matter and dark energy are in a rough proportion of 3:7. The time is right for a fresh new textbook which captures the state-of-the art in cosmology. Written by one of the world's leading cosmologists, this brand new, thoroughly class-tested textbook provides graduate and undergraduate students with coverage of the very latest developments and experimental results in the field. Prof. Nicola Vittorio shows what is meant by precision cosmology, from both theoretical and observational perspectives.
Inhomogeneous Universe Models with Varying Cosmological Term
Chimento, L P; Chimento, Luis P.; Pavon, Diego
1998-01-01
The evolution of a class of inhomogeneous spherically symmetric universe models possessing a varying cosmological term and a material fluid, with an adiabatic index either constant or not, is studied.
Current status of cosmological MDM model
Mikheeva, E V; Arkhipova, N A; Malinovsky, A M
2000-01-01
An analysis of cosmological models in spatially flat Friedmann Universe with cosmic gravitational wave background and zero $\\Lambda$-term is presented. The number of free parameters is equal to 5, they are $\\sigma_8$, $n$, $\\Omega_\
Standard Model Background of the Cosmological Collider
Chen, Xingang; Xianyu, Zhong-Zhi
2016-01-01
The inflationary universe can be viewed as a "Cosmological Collider" with energy of Hubble scale, producing very massive particles and recording their characteristic signals in primordial non-Gaussianities. To utilize this collider to explore any new physics at very high scales, it is a prerequisite to understand the background signals from the particle physics Standard Model. In this paper we describe the Standard Model background of the Cosmological Collider.
A Dynamical System Analysis of Three Fluid cosmological Model
Mahata, Nilanjana
2015-01-01
In Friedman-Robertson-Walker flat spacetime, we consider a three fluid cosmological model which contains dark matter, dark energy and baryonic matter in the form of perfect fluid with a barotropic equation of state. Dark matter is taken in form of dust and dark energy is described by a scalar field with a potential $V(\\phi)$. Einstein's field equations are reduced to an autonomous dynamical system by suitable redefinition of basic variables. Considering exponential potential for the scalar field, critical points are obtained for the autonomous system. Finally stability of the critical points and cosmological implications are analyzed.
Nonstandard cosmologies from physics beyond the Standard model
Khlopov, M. Yu.
2016-01-01
The modern cosmology is based on inflationary models with baryosynthesis and dark matter/energy.It implies extension of particle symmetry beyond the Standard model. Studies of physical basis of the modern cosmology combine direct searches for new physics at accelerators with its indirect non-accelerator probes, in which cosmological consequences of particle models play important role. The cosmological consequences of particle models inevitably go beyond the 'standard' cosmological $\\Lambda$CD...
Cosmological models with running cosmological term and decaying dark matter
Szydłowski, Marek; Stachowski, Aleksander
2017-03-01
We investigate the dynamics of the generalized ΛCDM model, which the Λ term is running with the cosmological time. On the example of the model Λ(t) =Λbare + α2/t2 we show the existence of a mechanism of the modification of the scaling law for energy density of dark matter: ρdm ∝a - 3 + λ(t). We use an approach developed by Urbanowski in which properties of unstable vacuum states are analyzed from the point of view of the quantum theory of unstable states. We discuss the evolution of Λ(t) term and pointed out that during the cosmic evolution there is a long phase in which this term is approximately constant. We also present the statistical analysis of both the Λ(t) CDM model with dark energy and decaying dark matter and the ΛCDM standard cosmological model. We use data such as Planck, SNIa, BAO, H(z) and AP test. While for the former we find the best fit value of the parameter Ωα2,0 is negative (energy transfer is from the dark matter to dark energy sector) and the parameter Ωα2,0 belongs to the interval (- 0 . 000040 , - 0 . 000383) at 2- σ level. The decaying dark matter causes to lowering a mass of dark matter particles which are lighter than CDM particles and remain relativistic. The rate of the process of decaying matter is estimated. Our model is consistent with the decaying mechanism producing unstable particles (e.g. sterile neutrinos) for which α2 is negative.
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.
Cosmological Implications of QGP Bulk Viscosity
Anand, Sampurn; Bhatt, Jitesh R
2016-01-01
Recent studies of the hot QCD matter indicate that the bulk viscosity ($\\zeta$) of quark-gluon plasma (QGP) rises sharply near the critical point of the QCD phase transition. In this work, we show that such a sharp rise of the bulk viscosity will lead to an effective negative pressure near the critical temperature, $T_{c}$ which in turn drives the Universe to inflate. This inflation has a natural graceful exist when the viscous effect evanesce. We estimate that, depending upon the peak value of $\\zeta$, universe expands by a factor of $10$ to $80$ times in a very short span ($\\Delta t\\sim 10^{-8}$ seconds). Another important outcome of the bulk viscosity dominated dynamics is the cavitation of QGP around $T \\sim 1.5T_{c}$. This would lead to the phenomenon of formation of cavitation bubbles within the QGP phase. The above scenario is independent of the order of QCD phase transition. We delineate some of the important cosmological consequences of the inflation and the cavitation.
Exacerbating the Cosmological Constant Problem with Interacting Dark Energy Models
Marsh, M. C. David
2017-01-01
Future cosmological surveys will probe the expansion history of the Universe and constrain phenomenological models of dark energy. Such models do not address the fine-tuning problem of the vacuum energy, i.e., the cosmological constant problem (CCP), but can make it spectacularly worse. We show that this is the case for "interacting dark energy" models in which the masses of the dark matter states depend on the dark energy sector. If realized in nature, these models have far-reaching implications for proposed solutions to the CCP that require the number of vacua to exceed the fine-tuning of the vacuum energy density. We show that current estimates of the number of flux vacua in string theory, Nvac˜O (1 0272 000) , are far too small to realize certain simple models of interacting dark energy and solve the cosmological constant problem anthropically. These models admit distinctive observational signatures that can be targeted by future gamma-ray observatories, hence making it possible to observationally rule out the anthropic solution to the cosmological constant problem in theories with a finite number of vacua.
Nonstandard cosmologies from physics beyond the Standard model
Khlopov, M Yu
2016-01-01
The modern cosmology is based on inflationary models with baryosynthesis and dark matter/energy.It implies extension of particle symmetry beyond the Standard model. Studies of physical basis of the modern cosmology combine direct searches for new physics at accelerators with its indirect non-accelerator probes, in which cosmological consequences of particle models play important role. The cosmological consequences of particle models inevitably go beyond the 'standard' cosmological $\\Lambda$CDM model and some possible feature of such 'nonstandard'cosmological scenarios is the subject of the present brief review.
Cosmological implications of a large complete quasar sample.
Segal, I E; Nicoll, J F
1998-04-28
Objective and reproducible determinations of the probabilistic significance levels of the deviations between theoretical cosmological prediction and direct model-independent observation are made for the Large Bright Quasar Sample [Foltz, C., Chaffee, F. H., Hewett, P. C., MacAlpine, G. M., Turnshek, D. A., et al. (1987) Astron. J. 94, 1423-1460]. The Expanding Universe model as represented by the Friedman-Lemaitre cosmology with parameters qo = 0, Lambda = 0 denoted as C1 and chronometric cosmology (no relevant adjustable parameters) denoted as C2 are the cosmologies considered. The mean and the dispersion of the apparent magnitudes and the slope of the apparent magnitude-redshift relation are the directly observed statistics predicted. The C1 predictions of these cosmology-independent quantities are deviant by as much as 11sigma from direct observation; none of the C2 predictions deviate by >2sigma. The C1 deviations may be reconciled with theory by the hypothesis of quasar "evolution," which, however, appears incapable of being substantiated through direct observation. The excellent quantitative agreement of the C1 deviations with those predicted by C2 without adjustable parameters for the results of analysis predicated on C1 indicates that the evolution hypothesis may well be a theoretical artifact.
Cosmological models with constant deceleration parameter
Energy Technology Data Exchange (ETDEWEB)
Berman, M.S.; de Mello Gomide, F.
1988-02-01
Berman presented elsewhere a law of variation for Hubble's parameter that yields constant deceleration parameter models of the universe. By analyzing Einstein, Pryce-Hoyle and Brans-Dicke cosmologies, we derive here the necessary relations in each model, considering a perfect fluid.
Gravitational lens models for cosmological black holes
Zakharov, A. F.; Capozziello, S.; Stornaiolo, C.
2017-03-01
If really such objects like cosmological black holes exist they may be studied with a standard technique like strong and weak gravitational lensing. Cosmological voids can be explained as the result the collapse of large perturbations into black hole with masses of the order of 1014 M ⊙ and the expansion of the universe. The resulting image of the universe is that it is more homogeneous than expected from present observations. In this paper we discuss some lensing properties related to the cosmological black holes (CBHs), namely we consider differences in gravitational lensing for point like mass and extended mass distributions. We consider the singular isothermal sphere model as a toy (illustrative) model for an extended distribution of dark matter and a slightly more complicated isothermal sphere with a core.
Hamiltonian Dynamics of Cosmological Quintessence Models
Ivanov, Rossen I
2016-01-01
The time-evolution dynamics of two nonlinear cosmological real gas models has been reexamined in detail with methods from the theory of Hamiltonian dynamical systems. These examples are FRWL cosmologies, one based on a gas, satisfying the van der Waals equation and another one based on the virial expansion gas equation. The cosmological variables used are the expansion rate, given by the Hubble parameter, and the energy density. The analysis is aided by the existence of global first integral as well as several special (second) integrals in each case. In addition, the global first integral can serve as a Hamiltonian for a canonical Hamiltonian formulation of the evolution equations. The conserved quantities lead to the existence of stable periodic solutions (closed orbits) which are models of a cyclic Universe. The second integrals allow for explicit solutions as functions of time on some special trajectories and thus for a deeper understanding of the underlying physics. In particular, it is shown that any pos...
Cosmological constraints on superconducting dark energy models
Keresztes, Zoltán; Harko, Tiberiu; Liang, Shi-Dong
2015-01-01
We consider cosmological tests of a scalar-vector-tensor gravitational model, in which the dark energy is included in the total action through a gauge invariant, electromagnetic type contribution. The ground state of dark energy, corresponding to a constant potential $V$ is a Bose-Einstein type condensate with spontaneously broken U(1) symmetry. In another words dark energy appears as a massive vector field emerging from a superposition of a massless vector and a scalar field, the latter corresponding to the Goldstone boson. Two particular cosmological models, corresponding to pure electric and pure magnetic type potentials, respectively are confronted with Type IA Supernovae and Hubble parameter data. In the electric case good fit is obtained along a narrow inclined stripe in the $\\Omega _{m}-\\Omega _{V}$ parameter plane, which includes the $\\Lambda $CDM limit. The other points on this admissible region represent superconducting dark energy as a sum of a cosmological constant and a time-evolving contribution...
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...
Cosmological perturbations from the Standard Model Higgs
Energy Technology Data Exchange (ETDEWEB)
Simone, Andrea De [SISSA, Via Bonomea 265, I-34136 Trieste (Italy); Riotto, Antonio, E-mail: andrea.desimone@sissa.it, E-mail: antonio.riotto@unige.ch [Department of Theoretical Physics and Center for Astroparticle Physics (CAP), 24 quai E. Ansermet, CH-1211 Geneva 4 (Switzerland)
2013-02-01
We propose that the Standard Model (SM) Higgs is responsible for generating the cosmological perturbations of the universe by acting as an isocurvature mode during a de Sitter inflationary stage. In view of the recent ATLAS and CMS results for the Higgs mass, this can happen if the Hubble rate during inflation is in the range (10{sup 10}−10{sup 14}) GeV (depending on the SM parameters). Implications for the detection of primordial tensor perturbations through the B-mode of CMB polarization via the PLANCK satellite are discussed. For example, if the Higgs mass value is confirmed to be m{sub h} = 125.5 GeV and m{sub t},α{sub s} are at their central values, our mechanism predicts tensor perturbations too small to be detected in the near future. On the other hand, if tensor perturbations will be detected by PLANCK through the B-mode of CMB, then there is a definite relation between the Higgs and top masses, making the mechanism predictive and falsifiable.
Minimally coupled scalar field cosmology in anisotropic cosmological model
Singh, C. P.; Srivastava, Milan
2017-02-01
We study a spatially homogeneous and anisotropic cosmological model in the Einstein gravitational theory with a minimally coupled scalar field. We consider a non-interacting combination of scalar field and perfect fluid as the source of matter components which are separately conserved. The dynamics of cosmic scalar fields with a zero rest mass and an exponential potential are studied, respectively. We find that both assumptions of potential along with the average scale factor as an exponential function of scalar field lead to the logarithmic form of scalar field in each case which further gives power-law form of the average scale factor. Using these forms of the average scale factor, exact solutions of the field equations are obtained to the metric functions which represent a power-law and a hybrid expansion, respectively. We find that the zero-rest-mass model expands with decelerated rate and behaves like a stiff matter. In the case of exponential potential function, the model decelerates, accelerates or shows the transition depending on the parameters. The isotropization is observed at late-time evolution of the Universe in the exponential potential model.
Minimally coupled scalar field cosmology in anisotropic cosmological model
Indian Academy of Sciences (India)
C P SINGH; MILAN SRIVASTAVA
2017-02-01
We study a spatially homogeneous and anisotropic cosmological model in the Einstein gravitational theory with a minimally coupled scalar field. We consider a non-interacting combination of scalar field and perfect fluid as the source of matter components which are separately conserved. The dynamics of cosmic scalar fields with a zero rest mass and an exponential potential are studied, respectively. We find that both assumptions of potential along with the average scale factor as an exponential function of scalar field lead to the logarithmic formof scalar field in each case which further gives power-law form of the average scale factor. Using these forms of the average scale factor, exact solutions of the field equations are obtained to the metric functions which represent a power-law and a hybrid expansion, respectively. We find that the zero-rest-mass model expands with decelerated rate and behaves like a stiff matter. In the case of exponential potential function, the model decelerates, accelerates or shows the transition depending on the parameters. The isotropization is observed at late-time evolution of the Universe in the exponential potential model.
Strictly isospectral Bianchi type II cosmological models
Rosu, H C; Obregón, O
1996-01-01
We show that, in the Q=0 factor ordering, the Wheeler-DeWitt equation for the Bianchi type ll model with the Ansatz \\rm \\Psi=A\\, e^{\\pm \\Phi(q^{\\mu})}, due to its one-dimensional character, may be approached by the strictly isospectral Darboux-Witten technique in standard supersymmetric quantum mechanics. One-parameter families of cosmological potentials and normalizable `wavefunctions of the universe' are exhibited. The isospectral method can be used to introduce normalizable wavefunctions in quantum cosmology.
Agegraphic dark energy: growth index and cosmological implications
Malekjani, M.; Basilakos, S.; Mehrabi, A.; Davari, Z.; Rezaei, M.
2017-01-01
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 cold dark matter (ΛCDM) 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 γ ≈ 5/9, which is close to that of the usual Λ cosmology, γ(Λ) ≈ 6/11. Finally, if the distribution of dark energy is clustered, then we obtain γ ≈ 1/2 which is ˜8 per cent smaller than that of the ΛCDM model.
On non-singular inhomogeneous cosmological models
Fernández-Jambrina, L
2009-01-01
In this talk we would like to review recent results on non-singular cosmological models. It has been recently shown that among stiff perfect fluid inhomogeneous spacetimes the absence of singularities is more common than it was expected in the literature. We would like to generalize these results and apply them to other matter sources.
A model with cosmological Bell inequalities
Maldacena, Juan
2015-01-01
We discuss the possibility of devising cosmological observables which violate Bell's inequalities. Such observables could be used to argue that cosmic scale features were produced by quantum mechanical effects in the very early universe. As a proof of principle, we propose a somewhat elaborate inflationary model where a Bell inequality violating observable can be constructed.
Astrophysical and cosmological implications of large volume string compactifications
Conlon, Joseph P.; Quevedo, Fernando
2007-08-01
We study the spectrum, couplings and cosmological and astrophysical implications of the moduli fields for the class of Calabi Yau IIB string compactifications for which moduli stabilisation leads to an exponentially large volume \\mathcal {V} \\sim 10^{15} l_{\\mathrm {s}}^6 and an intermediate string scale ms~1011 GeV, with TeV-scale observable supersymmetry breaking. All Kähler moduli except for the overall volume are heavier than the susy (supersymmetry) breaking scale, with m~ln(MP/m3/2)m3/2~(ln(MP/m3/2))2msusy~500 TeV and, contrary to standard expectations, have matter couplings suppressed only by the string scale rather than the Planck scale. These decay to matter early in the history of the universe, with a reheat temperature T~107 GeV, and are free from the cosmological moduli problem (CMP). The heavy moduli have a branching ratio to gravitino pairs of 10-30 and do not suffer from the gravitino overproduction problem. The overall volume modulus is a distinctive feature of these models and is an Mplanck-coupled scalar of mass m~1 MeV and subject to the CMP. A period of thermal inflation may help relax this problem. This field has a lifetime τ~1024 s and can contribute to dark matter. It may be detected through its decays to γγ or e+e-. If accessible the e+e- decay mode dominates, with \\mathrm {Br}(\\chi \\to \\gamma \\gamma) suppressed by a factor (ln(MP/m3/2))2. We consider the potential for detection of this field through different astrophysical sources: the Milky Way halo, the diffuse cosmic background and nearby galaxy clusters and find that the observed gamma ray background constrains \\Omega_{\\chi } \\lesssim 10^{-4} . The decays of this field may generate the 511 keV emission line from the galactic centre observed by INTEGRAL/SPI.
Realistic coasting cosmology from the Milne model
John, Moncy V
2016-01-01
In the context of the recent synchronicity problem in $\\Lambda$CDM cosmology, coasting models such as the classic Milne model and the $R_h=ct$ model have attracted much attention. Also, a very recent analysis of supernovae Ia data is reported to favour models with constant expansion rates. We point out that the nonempty $R_h=ct$ model has some known antecedents in the literature. Some of these are published even before the discovery of the accelerated expansion and were shown to have none of the cosmological problems and also that $H_0t_0=1$ and $\\Omega_m/\\Omega_{dark \\; energy}$ = some constant of the order of unity. In this paper, we also derive such a model by a complex extension of scale factor in the Milne model.
Constraining Cosmological Models with Different Observations
Wei, J. J.
2016-07-01
With the observations of Type Ia supernovae (SNe Ia), scientists discovered that the Universe is experiencing an accelerated expansion, and then revealed the existence of dark energy in 1998. Since the amazing discovery, cosmology has became a hot topic in the physical research field. Cosmology is a subject that strongly depends on the astronomical observations. Therefore, constraining different cosmological models with all kinds of observations is one of the most important research works in the modern cosmology. The goal of this thesis is to investigate cosmology using the latest observations. The observations include SNe Ia, Type Ic Super Luminous supernovae (SLSN Ic), Gamma-ray bursts (GRBs), angular diameter distance of galaxy cluster, strong gravitational lensing, and age measurements of old passive galaxies, etc. In Chapter 1, we briefly review the research background of cosmology, and introduce some cosmological models. Then we summarize the progress on cosmology from all kinds of observations in more details. In Chapter 2, we present the results of our studies on the supernova cosmology. The main difficulty with the use of SNe Ia as standard candles is that one must optimize three or four nuisance parameters characterizing SN luminosities simultaneously with the parameters of an expansion model of the Universe. We have confirmed that one should optimize all of the parameters by carrying out the method of maximum likelihood estimation in any situation where the parameters include an unknown intrinsic dispersion. The commonly used method, which estimates the dispersion by requiring the reduced χ^{2} to equal unity, does not take into account all possible variances among the parameters. We carry out such a comparison of the standard ΛCDM cosmology and the R_{h}=ct Universe using the SN Legacy Survey sample of 252 SN events, and show that each model fits its individually reduced data very well. Moreover, it is quite evident that SLSNe Ic may be useful
Cosmological Models with Time Dependent G and A Coupling Scalars
Institute of Scientific and Technical Information of China (English)
N.Ibotombi Singh; S.Kiranmla Chanu; S.Surendra Singh
2009-01-01
A cosmological model in which the universe has its critical density and gravitational constants generalized as coupling scalars in Einstein's theory is considered.A general method of solving the field equations is given.An exact solution for matter distribution in cosmological models satisfying G = Go(R/Ro)n is presented.Corresponding physical interpretations of the cosmological solutions are also discussed.
QCD nature of dark energy at finite temperature: cosmological implications
Azizi, K
2015-01-01
The Veneziano ghost field has been proposed as an alternative source of dark energy whose energy density is consistent with the cosmological observations. In this model, the energy density of QCD ghost field is expressed in terms of QCD degrees of freedom at zero temperature. We extend this model to finite temperature to search the model predictions from the late time to the early universe. We depict the variations of QCD parameters entering the calculations, dark energy density, equation of state, Hubble and deceleration parameters on temperature from zero to a critical temperature. We compare our results with the observations and theoretical predictions existing at different eras.It is found that this model safely define the universe from quark condensation up to now and its predictions are not in tension with those of the standard cosmology. The finite temperature ghost dark energy predictions on the Hubble parameter slightly better fit to observations compared to those of zero temperature.
Cosmological implications of quantum entanglement in the multiverse
Kanno, Sugumi
2015-12-01
We explore the cosmological implications of quantum entanglement between two causally disconnected universes in the multiverse. We first consider two causally separated de Sitter spaces with a state which is initially entangled. We derive the reduced density matrix of our universe and compute the spectrum of vacuum fluctuations. We then consider the same system with an initially non-entangled state. We find that due to quantum interference scale dependent modulations may enter the spectrum for the case of initially non-entangled state. This gives rise to the possibility that the existence of causally disconnected universes may be experimentally tested by analyzing correlators in detail.
Cosmological implications of quantum entanglement in the multiverse
Kanno, Sugumi
2015-01-01
We explore the cosmological implications of quantum entanglement between two causally disconnected universes in the multiverse. We first consider two causally separated de Sitter spaces with a state which is initially entangled. We derive the reduced density matrix of our universe and compute the spectrum of vacuum fluctuations. We then consider the same system with an initially non-entangled state. We find that scale dependent modulations may enter the spectrum for the case of initially non-entangled state due to quantum interference. This gives rise to the possibility that the existence of causally disconnected universes may be experimentally tested by analyzing correlators in detail.
Cosmological implications of quantum entanglement in the multiverse
Energy Technology Data Exchange (ETDEWEB)
Kanno, Sugumi, E-mail: sugumi.kanno@ehu.es [Department of Theoretical Physics and History of Science, University of the Basque Country UPV/EHU, 48080 Bilbao (Spain); IKERBASQUE, Basque Foundation for Science, Maria Diaz de Haro 3, 48013 Bilbao (Spain)
2015-12-17
We explore the cosmological implications of quantum entanglement between two causally disconnected universes in the multiverse. We first consider two causally separated de Sitter spaces with a state which is initially entangled. We derive the reduced density matrix of our universe and compute the spectrum of vacuum fluctuations. We then consider the same system with an initially non-entangled state. We find that due to quantum interference scale dependent modulations may enter the spectrum for the case of initially non-entangled state. This gives rise to the possibility that the existence of causally disconnected universes may be experimentally tested by analyzing correlators in detail.
Cosmological implications of quantum entanglement in the multiverse
Directory of Open Access Journals (Sweden)
Sugumi Kanno
2015-12-01
Full Text Available We explore the cosmological implications of quantum entanglement between two causally disconnected universes in the multiverse. We first consider two causally separated de Sitter spaces with a state which is initially entangled. We derive the reduced density matrix of our universe and compute the spectrum of vacuum fluctuations. We then consider the same system with an initially non-entangled state. We find that due to quantum interference scale dependent modulations may enter the spectrum for the case of initially non-entangled state. This gives rise to the possibility that the existence of causally disconnected universes may be experimentally tested by analyzing correlators in detail.
Homogeneous cosmological models and new inflation
Turner, Michael S.; Widrow, Lawrence M.
1986-01-01
The promise of the inflationary-universe scenario is to free the present state of the universe from extreme dependence upon initial data. Paradoxically, inflation is usually analyzed in the context of the homogeneous and isotropic Robertson-Walker cosmological models. It is shown that all but a small subset of the homogeneous models undergo inflation. Any initial anisotropy is so strongly damped that if sufficient inflation occurs to solve the flatness and horizon problems, the universe today would still be very isotropic.
Starobinsky cosmological model in Palatini formalism
Energy Technology Data Exchange (ETDEWEB)
Stachowski, Aleksander [Jagiellonian University, Astronomical Observatory, Krakow (Poland); Szydlowski, Marek [Jagiellonian University, Astronomical Observatory, Krakow (Poland); Jagiellonian University, Mark Kac Complex Systems Research Centre, Krakow (Poland); Borowiec, Andrzej [Wroclaw University, Institute for Theoretical Physics, Wroclaw (Poland)
2017-06-15
We classify singularities in FRW cosmologies, which dynamics can be reduced to the dynamical system of the Newtonian type. This classification is performed in terms of the geometry of a potential function if it has poles. At the sewn singularity, which is of a finite scale factor type, the singularity in the past meets the singularity in the future. We show that such singularities appear in the Starobinsky model in f(R) = R + γR{sup 2} in the Palatini formalism, when dynamics is determined by the corresponding piecewise-smooth dynamical system. As an effect we obtain a degenerate singularity. Analytical calculations are given for the cosmological model with matter and the cosmological constant. The dynamics of model is also studied using dynamical system methods. From the phase portraits we find generic evolutionary scenarios of the evolution of the universe. For this model, the best fit value of Ω{sub γ} = 3γH{sub 0}{sup 2} is equal 9.70 x 10{sup -11}. We consider a model in both Jordan and Einstein frames. We show that after transition to the Einstein frame we obtain both the form of the potential of the scalar field and the decaying Lambda term. (orig.)
Testing Nonstandard Cosmological Models with SNLS3 Supernova Data and Other Cosmological Probes
Li, Zhengxiang; Wu, Puxun; Yu, Hongwei
2012-01-01
We investigate the implications for some nonstandard cosmological models using data from the first three years of the Supernova Legacy Survey (SNLS3), assuming a spatially flat universe. A comparison between the constraints from the SNLS3 and those from other SN Ia samples, such as the ESSENCE, Union2, SDSS-II, and Constitution samples, is given and the effects of different light-curve fitters are considered. We find that analyzing SNe Ia with SALT2 or SALT or SiFTO can give consistent results and the tensions between different data sets and different light-curve fitters are obvious for fewer-free-parameters models. At the same time, we also study the constraints from SNLS3 along with data from the cosmic microwave background and the baryonic acoustic oscillations (CMB/BAO), and the latest Hubble parameter versus redshift (H(z)). Using model selection criteria such as χ2/dof, goodness of fit, Akaike information criterion, and Bayesian information criterion, we find that, among all the cosmological models considered here (ΛCDM, constant w, varying w, Dvali-Gabadadze-Porrati (DGP), modified polytropic Cardassian, and the generalized Chaplygin gas), the flat DGP is favored by SNLS3 alone. However, when additional CMB/BAO or H(z) constraints are included, this is no longer the case, and the flat ΛCDM becomes preferred.
TESTING NONSTANDARD COSMOLOGICAL MODELS WITH SNLS3 SUPERNOVA DATA AND OTHER COSMOLOGICAL PROBES
Energy Technology Data Exchange (ETDEWEB)
Li Zhengxiang; Yu Hongwei [Department of Physics and Key Laboratory of Low Dimensional Quantum Structures and Quantum Control of the Ministry of Education, Hunan Normal University, Changsha, Hunan 410081 (China); Wu Puxun, E-mail: hwyu@hunnu.edu.cn [Center of Nonlinear Science and Department of Physics, Ningbo University, Ningbo, Zhejiang 315211 (China)
2012-01-10
We investigate the implications for some nonstandard cosmological models using data from the first three years of the Supernova Legacy Survey (SNLS3), assuming a spatially flat universe. A comparison between the constraints from the SNLS3 and those from other SN Ia samples, such as the ESSENCE, Union2, SDSS-II, and Constitution samples, is given and the effects of different light-curve fitters are considered. We find that analyzing SNe Ia with SALT2 or SALT or SiFTO can give consistent results and the tensions between different data sets and different light-curve fitters are obvious for fewer-free-parameters models. At the same time, we also study the constraints from SNLS3 along with data from the cosmic microwave background and the baryonic acoustic oscillations (CMB/BAO), and the latest Hubble parameter versus redshift (H(z)). Using model selection criteria such as {chi}{sup 2}/dof, goodness of fit, Akaike information criterion, and Bayesian information criterion, we find that, among all the cosmological models considered here ({Lambda}CDM, constant w, varying w, Dvali-Gabadadze-Porrati (DGP), modified polytropic Cardassian, and the generalized Chaplygin gas), the flat DGP is favored by SNLS3 alone. However, when additional CMB/BAO or H(z) constraints are included, this is no longer the case, and the flat {Lambda}CDM becomes preferred.
Starobinsky cosmological model in Palatini formalism
Stachowski, Aleksander; Borowiec, Andrzej
2016-01-01
We classify singularities in FRW cosmologies, which dynamics can be reduced to the dynamical system of the Newtonian type. This classification is performed in terms of geometry of a potential function if it has poles. At the sewn singularity, which is of a type of the finite scale factor, the singularity in the past meets the singularity in the future. We show, that such singularities appear in the Starobinsky model in $f(\\hat{R})=\\hat{R}+\\gamma \\hat{R}^2$ in the Palatini formalism, when dynamics is determined by the corresponding piece-wise smooth dynamical system. As an effect we obtain a degenerated singularity, which can be interpreted as a place, when history of the Universe ends and originates simultaneously. Detailed analytical calculations are given for the cosmological model with matter and the cosmological constant in the Starobinsky model. In this case we obtain an exact formula for values of redshift at the singularity points. The dynamics of model is also studied using dynamical system methods wh...
$C$-field cosmological models: revisited
Yadav, A K; Ray, Saibal; Rahaman, F; Sardar, I H
2015-01-01
We investigate plane symmetric space-time filled with perfect fluid in the $C$-field cosmology of Hoyle and Narlikar. A new class of exact solutions have been obtained by considering the creation field $C$ as a function of time only. To get the deterministic solution, it has been assumed that the rate of creation of matter-energy density is proportional to the strength of the existing $C$-field energy density. Several physical aspects and geometrical properties of the models are discussed in detail, especially it is shown that some of our solutions of $C$-field cosmology are free from singularity in contrast to the Big Bang cosmology. A comparative study has been carried out between two models, one singular and the other nonsingular, by contrasting the behaviour of the physical parameters and noted that the model in a unique way represents both the features of the accelerating as well as decelerating Universe depending on the parameters and thus seems provides glimpses of the oscillating or cyclic model of th...
The simplest possible bouncing quantum cosmological model
Peter, Patrick
2016-01-01
We present and expand the simplest possible quantum cosmological model already discussed in a previous work: the trajectory formulation of quantum mechanics applied to cosmology in the FLRW minisuperspace without spatial curvature. The initial conditions that were assumed there were such that the wave function would not change its functional form but instead provide a dynamics to its parameters. Here, we consider a more general situation, in practice consisting of modified Gaussian wave functions, aiming at obtaining a bounce from a contracting phase. Whereas previous works consistently obtain very symmetric bounces, we find that it is possible to produce highly non symmetric solutions, and even cases for which multiple bounces naturally occur. We also introduce a means of treating the shear in this category of models by quantizing in the Bianchi I minisuperpace.
The simplest possible bouncing quantum cosmological model
Peter, Patrick; Vitenti, Sandro D. P.
2016-06-01
We present and expand the simplest possible quantum cosmological bouncing model already discussed in previous works: the trajectory formulation of quantum mechanics applied to cosmology (through the Wheeler-De Witt equation) in the Friedmann-Lemaître-Robertson-Walker (FLRW) minisuperspace without spatial curvature. The initial conditions that were previously assumed were such that the wave function would not change its functional form but instead provide a dynamics to its parameters. Here, we consider a more general situation, in practice consisting of modified Gaussian wave functions, aiming at obtaining a nonsingular bounce from a contracting phase. Whereas previous works consistently obtain very symmetric bounces, we find that it is possible to produce highly non-symmetric solutions, and even cases for which multiple bounces naturally occur. We also introduce a means of treating the shear in this category of models by quantizing in the Bianchi I minisuperspace.
Arbitrary scalar field and quintessence cosmological models
Harko, Tiberiu; Mak, M K
2014-01-01
The mechanism of the initial inflationary scenario of the universe and of its late-time acceleration can be described by assuming the existence of some gravitationally coupled scalar fields $\\phi $, with the inflaton field generating inflation and the quintessence field being responsible for the late accelerated expansion. Various inflationary and late-time accelerated scenarios are distinguished by the choice of an effective self-interaction potential $V(\\phi)$, which simulates a temporarily non-vanishing cosmological term. In this work, we present a new formalism for the analysis of scalar fields in flat isotropic and homogeneous cosmological models. The basic evolution equation of the models can be reduced to a first order non-linear differential equation. Approximate solutions of this equation can be constructed in the limiting cases of the scalar field kinetic energy and potential energy dominance, respectively, as well as in the intermediate regime. Moreover, we present several new accelerating and dece...
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.
Past Eras In Cyclic Cosmological Models
Frampton, Paul H
2009-01-01
In infinitely cyclic cosmology past eras are discussed using set theory and transfinite numbers. One consistent scenario, already in the literature, is where there is always a countably infinite number, $\\aleph_0$, of universes and no big bang. I describe here an alternative where the present number of universes is $\\aleph_0$ and in the infinite past there was only a finite number of universes. In this alternative model it is also possible that there was no big bang.
Inextendibility of expanding cosmological models with symmetry
Energy Technology Data Exchange (ETDEWEB)
Dafermos, Mihalis [University of Cambridge, Department of Pure Mathematics and Mathematical Statistics, Wilberforce Road, Cambridge CB3 0WB (United Kingdom); Rendall, Alan D [Max Planck Institute for Gravitational Physics, Albert Einstein Institute, Am Muehlenberg 1, D-14476 Golm (Germany)
2005-12-07
A new criterion for inextendibility of expanding cosmological models with symmetry is presented. It is applied to derive a number of new results and to simplify the proofs of existing ones. In particular, it shows that the solutions of the Einstein-Vlasov system with T{sup 2} symmetry, including the vacuum solutions, are inextendible in the future. The technique introduced adds a qualitatively new element to the available tool-kit for studying strong cosmic censorship. (letter to the editor)
The best-fit universe. [cosmological models
Turner, Michael S.
1991-01-01
Inflation provides very strong motivation for a flat Universe, Harrison-Zel'dovich (constant-curvature) perturbations, and cold dark matter. However, there are a number of cosmological observations that conflict with the predictions of the simplest such model: one with zero cosmological constant. They include the age of the Universe, dynamical determinations of Omega, galaxy-number counts, and the apparent abundance of large-scale structure in the Universe. While the discrepancies are not yet serious enough to rule out the simplest and most well motivated model, the current data point to a best-fit model with the following parameters: Omega(sub B) approximately equal to 0.03, Omega(sub CDM) approximately equal to 0.17, Omega(sub Lambda) approximately equal to 0.8, and H(sub 0) approximately equal to 70 km/(sec x Mpc) which improves significantly the concordance with observations. While there is no good reason to expect such a value for the cosmological constant, there is no physical principle that would rule out such.
The best-fit universe. [cosmological models
Turner, Michael S.
1991-01-01
Inflation provides very strong motivation for a flat Universe, Harrison-Zel'dovich (constant-curvature) perturbations, and cold dark matter. However, there are a number of cosmological observations that conflict with the predictions of the simplest such model: one with zero cosmological constant. They include the age of the Universe, dynamical determinations of Omega, galaxy-number counts, and the apparent abundance of large-scale structure in the Universe. While the discrepancies are not yet serious enough to rule out the simplest and most well motivated model, the current data point to a best-fit model with the following parameters: Omega(sub B) approximately equal to 0.03, Omega(sub CDM) approximately equal to 0.17, Omega(sub Lambda) approximately equal to 0.8, and H(sub 0) approximately equal to 70 km/(sec x Mpc) which improves significantly the concordance with observations. While there is no good reason to expect such a value for the cosmological constant, there is no physical principle that would rule out such.
Cosmological implications of baryon acoustic oscillation (BAO) measurements
Aubourg, Éric; Bautista, Julian E; Beutler, Florian; Bhardwaj, Vaishali; Bizyaev, Dmitry; Blanton, Michael; Blomqvist, Michael; Bolton, Adam S; Bovy, Jo; Brewington, Howard; Brinkmann, J; Brownstein, Joel R; Burden, Angela; Busca, Nicolás G; Carithers, William; Chuang, Chia-Hsun; Comparat, Johan; Cuesta, Antonio J; Dawson, Kyle S; Delubac, Timothée; Eisenstein, Daniel J; Font-Ribera, Andreu; Ge, Jian; Goff, J -M Le; Gontcho, Satya Gontcho A; Gott, J Richard; Gunn, James E; Guo, Hong; Guy, Julien; Hamilton, Jean-Christophe; Ho, Shirley; Honscheid, Klaus; Howlett, Cullan; Kirkby, David; Kitaura, Francisco S; Kneib, Jean-Paul; Lee, Khee-Gan; Long, Dan; Lupton, Robert H; Magaña, Mariana Vargas; Malanushenko, Viktor; Malanushenko, Elena; Manera, Marc; Maraston, Claudia; Margala, Daniel; McBride, Cameron K; Miralda-Escudé, Jordi; Myers, Adam D; Nichol, Robert C; Noterdaeme, Pasquier; Nuza, Sebastián E; Olmstead, Matthew D; Oravetz, Daniel; Pâris, Isabelle; Padmanabhan, Nikhil; Palanque-Delabrouille, Nathalie; Pan, Kaike; Pellejero-Ibanez, Marcos; Percival, Will J; Petitjean, Patrick; Pieri, Matthew M; Prada, Francisco; Reid, Beth; Roe, Natalie A; Ross, Ashley J; Ross, Nicholas P; Rossi, Graziano; Rubiño-Martín, Jose Alberto; Sánchez, Ariel G; Samushia, Lado; Santos, Ricardo Tanausú Génova; Scóccola, Claudia G; Schlegel, David J; Schneider, Donald P; Seo, Hee-Jong; Sheldon, Erin; Simmons, Audrey; Skibba, Ramin A; Slosar, Anže; Strauss, Michael A; Thomas, Daniel; Tinker, Jeremy L; Tojeiro, Rita; Vazquez, Jose Alberto; Viel, Matteo; Wake, David A; Weaver, Benjamin A; Weinberg, David H; Wood-Vasey, W M; Yèche, Christophe; Zehavi, Idit; Zhao, Gong-Bo
2014-01-01
We derive constraints on cosmological parameters and tests of dark energy models from the combination of baryon acoustic oscillation (BAO) measurements with cosmic microwave background (CMB) and Type Ia supernova (SN) data. We take advantage of high-precision BAO measurements from galaxy clustering and the Ly-alpha forest (LyaF) in the BOSS survey of SDSS-III. BAO data alone yield a high confidence detection of dark energy, and in combination with the CMB angular acoustic scale they further imply a nearly flat universe. Combining BAO and SN data into an "inverse distance ladder" yields a 1.7% measurement of $H_0=67.3 \\pm1.1$ km/s/Mpc. This measurement assumes standard pre-recombination physics but is insensitive to assumptions about dark energy or space curvature, so agreement with CMB-based estimates that assume a flat LCDM cosmology is an important corroboration of this minimal cosmological model. For open LCDM, our BAO+SN+CMB combination yields $\\Omega_m=0.301 \\pm 0.008$ and curvature $\\Omega_k=-0.003 \\pm ...
Cosmological aspects of a vector field model
Sadatian, S Davood
2012-01-01
We have studied a DGP-inspired braneworld scenario where the idea of Lorentz invariance violation has been combined into a specifying preferred frame that embed a dynamical normal vector field to brane. We propose the Lorentz violating DGP brane models with enough parameters can explain crossing of phantom divide line. Also we have considered the model for proper cosmological evolution that is according to the observed behavior of the equation of state. In other view point, we have described a Rip singularity solution of model that occur in this model.
Energy Technology Data Exchange (ETDEWEB)
Davis, Tamara M.; Mortsell, E.; Sollerman, J.; Becker, A.C.; Blondin, S.; Challis, P.; Clocchiatti, A.; Filippenko, A.V.; Foley, R.J.; Garnavich, P.M.; Jha, S.; Krisciunas, K.; Kirshner, R.P.; Leibundgut, B.; Li, W.; Matheson, T.; Miknaitis, G.; Pignata, G.; Rest, A.; Riess, A.G.; Schmidt, B.P.; /Bohr Inst. /Stockholm U. /Washington U.,
2007-01-25
The first cosmological results from the ESSENCE supernova survey (Wood-Vasey et al. 2007) are extended to a wider range of cosmological models including dynamical dark energy and non-standard cosmological models. We fold in a greater number of external data sets such as the recent Higher-z release of high-redshift supernovae (Riess et al. 2007) as well as several complementary cosmological probes. Model comparison statistics such as the Bayesian and Akaike information criteria are applied to gauge the worth of models. These statistics favor models that give a good fit with fewer parameters. Based on this analysis, the preferred cosmological model is the flat cosmological constant model, where the expansion history of the universe can be adequately described with only one free parameter describing the energy content of the universe. Amongst the more exotic models that provide good fits to the data, we note a preference for models whose best-fit parameters reduce them to the cosmological constant model.
A classical cosmological model for triviality
Salehi, H; Rashidi, R
2004-01-01
The aim of this paper is to study the triviality of $\\lambda\\phi^{4}$ theory in a classical gravitational model. Starting from a conformal invariant scalar tensor theory with a self-interaction term $\\lambda\\phi^{4}$, we investigate the effect of a conformal symmetry breaking emerging from the gravitational coupling of the large-scale distribution of matter in the universe. Taking in this cosmological symmetry breaking phase the infinite limit of the maximal length (the size of the universe) and the zero limit of the minimal length (the Planck length) implies triviality, i.e. a vanishing coupling constant $\\lambda$. It suggests that the activity of the self-interaction term $\\lambda\\phi^{4}$ in the cosmological context implies that the universe is finite and a minimal fundamental length exists.
Hybrid models in loop quantum cosmology
Elizaga Navascués, Beatriz; Martín-Benito, Mercedes; Mena Marugán, Guillermo A.
2016-06-01
In the framework of Loop Quantum Cosmology (LQC), inhomogeneous models are usually quantized by means of a hybrid approach that combines loop quantization techniques with standard quantum field theory methods. This approach is based on a splitting of the phase space in a homogeneous sector, formed by global, zero-modes and an inhomogeneous sector, formed by the remaining, infinite number of modes, that describe the local degrees of freedom. Then, the hybrid quantization is attained by adopting a loop representation for the homogeneous gravitational sector, while a Fock representation is used for the inhomogeneities. The zero-mode of the Hamiltonian constraint operator couples the homogeneous and inhomogeneous sectors. The hybrid approach, therefore, is expected to provide a suitable quantum theory in regimes where the main quantum effects of the geometry are those affecting the zero-modes, while the inhomogeneities, still being quantum, can be treated in a more conventional way. This hybrid strategy was first proposed for the simplest cosmological midisuperspaces: the Gowdy models, and it has been later applied to the case of cosmological perturbations. This paper reviews the construction and main applications of hybrid LQC.
Cosmological models in general relativity
Indian Academy of Sciences (India)
B B Paul
2003-12-01
LRS Bianchi type-I space-time ﬁlled with perfect ﬂuid is considered here with deceleration parameter as variable. The metric potentials and are functions of as well as . Assuming '/=(), where prime denotes differentiation with respect to , it was found that =('/) and =(), where =() and is the scale factor which is a function of only. The value of Hubble’s constant 0 was found to be less than half for non-ﬂat model and is equal to 1.3 for a ﬂat model.
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}\
Beyond the Cosmological Standard Model
Joyce, Austin; Khoury, Justin; Trodden, Mark
2014-01-01
After a decade and a half of research motivated by the accelerating universe, theory and experiment have a reached a certain level of maturity. The development of theoretical models beyond \\Lambda, or smooth dark energy, often called modified gravity, has led to broader insights into a path forward, and a host of observational and experimental tests have been developed. In this review we present the current state of the field and describe a framework for anticipating developments in the next decade. We identify the guiding principles for rigorous and consistent modifications of the standard model, and discuss the prospects for empirical tests. We begin by reviewing attempts to consistently modify Einstein gravity in the infrared, focusing on the notion that additional degrees of freedom introduced by the modification must screen themselves from local tests of gravity. We categorize screening mechanisms into three broad classes: mechanisms which become active in regions of high Newtonian potential, those in wh...
Density contrast indicators in cosmological dust models
Indian Academy of Sciences (India)
Filipe C Mena; Reza Tavakol
2000-10-01
We discuss ways of quantifying structuration in relativistic cosmological settings, by employing a family of covariant density constrast indicators. We study the evolution of these indicators with time in the context of inhomogeneous Szekeres models. We ﬁnd that different observers (having either different spatial locations or different indicators) see different evolutions for the density contrast, which may or may not be monotonically increasing with time. We also ﬁnd that monotonicity seems to be related to the initial conditions of the model, which may be of potential interest in connection with debates regarding gravitational entropy and the arrow of time.
Testing cosmological models with COBE data
Energy Technology Data Exchange (ETDEWEB)
Torres, S. [Observatorio Astronomico, Bogota` (Colombia)]|[Centro Internacional de Fisica, Bogota` (Colombia); Cayon, L. [Lawrence Berkeley Laboratory and Center for Particle Astrophysics, Berkeley (United States); Martinez-Gonzalez, E.; Sanz, J. L. [Santander, Univ. de Cantabria (Spain). Instituto de Fisica. Consejo Superior de Investigaciones Cientificas
1997-02-01
The authors test cosmological models with {Omega} < 1 using the COBE two-year cross-correlation function by means of a maximum-likelihood test with Monte Carlo realizations of several {Omega} models. Assuming a Harrison-Zel`dovich primordial power spectrum with amplitude {proportional_to} Q, it is found that there is a large region in the ({Omega}, Q), parameter space that fits the data equally well. They find that the flatness of the universe is not implied by the data. A summary of other analyses of COBE data to constrain the shape of the primordial spectrum is presented.
Cosmological Implications of the Uncertainty in H- Destruction Rate Coefficients
Glover, S C O; Jappsen, A K; Glover, Simon C.O.; Savin, Daniel W.; Jappsen, Anne-Katharina
2006-01-01
In primordial gas, molecular hydrogen forms primarily through associative detachment of H- and H, thereby destroying the H-. The H- anion can also be destroyed by a number of other reactions, most notably by mutual neutralization with protons. However, neither the associative detachment nor the mutual neutralization rate coefficients are well determined: both may be uncertain by as much as an order of magnitude. This introduces a corresponding uncertainty into the H2 formation rate, which may have cosmological implications. Here, we examine the effect that these uncertainties have on the formation of H2 and the cooling of protogalactic gas in a variety of situations. We show that the effect is particularly large for protogalaxies forming in previously ionized regions, affecting our predictions of whether or not a given protogalaxy can cool and condense within a Hubble time, and altering the strength of the ultraviolet background that is required to prevent collapse.
Cosmological modelling with Regge calculus
Liu, Rex G
2015-01-01
The late universe's matter distribution obeys the Copernican principle at only the coarsest of scales. The relative importance of such inhomogeneity is still not well understood. Because of the Einstein field equations' non-linear nature, some argue a non-perturbative approach is necessary to correctly model inhomogeneities and may even obviate any need for dark energy. We shall discuss an approach based on Regge calculus, a discrete approximation to general relativity: we shall discuss the Collins--Williams formulation of Regge calculus and its application to two toy universes. The first is a universe for which the continuum solution is well-established, the $\\Lambda$-FLRW universe. The second is an inhomogeneous universe, the `lattice universe' wherein matter consists solely of a lattice of point masses with pure vacuum in between, a distribution more similar to that of the actual universe compared to FLRW universes. We shall discuss both regular lattices and one where one mass gets perturbed.
Inflation in the standard cosmological model
Uzan, Jean-Philippe
2015-12-01
The inflationary paradigm is now part of the standard cosmological model as a description of its primordial phase. While its original motivation was to solve the standard problems of the hot big bang model, it was soon understood that it offers a natural theory for the origin of the large-scale structure of the universe. Most models rely on a slow-rolling scalar field and enjoy very generic predictions. Besides, all the matter of the universe is produced by the decay of the inflaton field at the end of inflation during a phase of reheating. These predictions can be (and are) tested from their imprint of the large-scale structure and in particular the cosmic microwave background. Inflation stands as a window in physics where both general relativity and quantum field theory are at work and which can be observationally studied. It connects cosmology with high-energy physics. Today most models are constructed within extensions of the standard model, such as supersymmetry or string theory. Inflation also disrupts our vision of the universe, in particular with the ideas of chaotic inflation and eternal inflation that tend to promote the image of a very inhomogeneous universe with fractal structure on a large scale. This idea is also at the heart of further speculations, such as the multiverse. This introduction summarizes the connections between inflation and the hot big bang model and details the basics of its dynamics and predictions. xml:lang="fr"
Dynamics in Nonlocal Cosmological Models Derived from String Field Theory
Joukovskaya, Liudmila
2007-01-01
A general class of nonlocal cosmological models is considered. A new method for solving nonlocal Friedmann equations is proposed, and solutions of the Friedmann equations with nonlocal operator are presented. The cosmological properties of these solutions are discussed. Especially indicated is $p$-adic cosmological model in which we have obtained nonsingular bouncing solution and string field theory tachyon model in which we have obtained full solution of nonlocal Friedmann equations with $w=...
Considering Late-Time Acceleration in Some Cosmological Models
Directory of Open Access Journals (Sweden)
S. Davood Sadatian
2013-01-01
Full Text Available We study two cosmological models: a nonminimally coupled scalar field on brane world model and a minimally coupled scalar field on Lorentz invariance violation model. We compare some cosmological results in these scenarios. Also, we consider some types of Rip singularity solution in both models.
Standard cosmological evolution in the f(R) model to Kaluza-Klein cosmology
Energy Technology Data Exchange (ETDEWEB)
Aghmohammadi, A; Abolhassani, M R [Plasma Physics Research Center, Science and Research Branch, Islamic Azad University of Tehran (Iran, Islamic Republic of); Saaidi, Kh; Vajdi, A [Department of Physics, Faculty of Science, University of Kurdistan, Pasdaran Ave., Sanandaj (Iran, Islamic Republic of)], E-mail: agha35484@yahoo.com, E-mail: ksaaidi@uok.ac.ir, E-mail: mrhasani@modares.ac.ir, E-mail: Avajdi@uok.ac.ir
2009-12-15
In this paper, using f(R) theory of gravity we explicitly calculate cosmological evolution in the presence of a perfect fluid source in four- and five-dimensional space-time in which this cosmological evolution in self-creation is presented by Reddy et al (2009 Int. J. Theor. Phys. 48 10). An exact cosmological model is presented using a relation between Einstein's gravity field equation components due to a metric with the same component from f(R) theory of gravity. Some physics and kinematical properties of the model are also discussed.
Piecewise Silence in Discrete Cosmological Models
Clifton, Timothy; Rosquist, Kjell
2014-01-01
We consider a family of cosmological models in which all mass is confined to a regular lattice of identical black holes. By exploiting the reflection symmetry about planes that bisect these lattices into identical halves, we are able to consider the evolution of a number of geometrically distinguished surfaces that exist within each of them. We show that gravitational waves are effectively trapped within small chambers for all time, and are not free to propagate throughout the space-time. Each chamber therefore evolves as if it were in isolation from the rest of the universe. We call this phenomenon "piecewise silence".
A New Class of Cosmologically `Viable' $f(R)$ Models
Kumar, Rohin
2016-01-01
Instead of assuming a form of gravity and demand cosmology fit with $\\Lambda CDM$, a potentially `viable' $f(R)$ gravity model is derived assuming an alternative model of cosmology. Taking the `designer' approach to $f(R)$, a new class of solutions are derived starting with linear coasting cosmology in which scale factor linearly increases with time during matter domination. The derived forms of $f(R)$ are presented as result.
Cosmological applications of the Szekeres model
Bolejko, K
2006-01-01
This paper presents the cosmological applications of the quasispherical Szekeres model. The quasispherical Szekeres model is an exact solution of the Einstein field equations, which represents a time-dependent mass dipole superposed on a monopole and therefore is suitable for modelling double structures such as voids and adjourning galaxy superclusters. Moreover, as the Szekeres model is an exact solution of the Einstein equations it enables tracing light and estimation of the impact of cosmic structures on light propagation. This paper presents the evolution of a void and adjourning supercluster and also reports on how the Szekeres model might be employed either for the estimation of mass of galaxies clusters or for the estimation of the luminosity distance.
Structure formation in the DGP cosmological model
Koyama, K; Koyama, Kazuya; Maartens, Roy
2006-01-01
The DGP brane-world model provides an alternative to the standard LCDM cosmology, in which the late universe accelerates due to a modification of gravity rather than vacuum energy. The cosmological constant $\\Lambda$ in LCDM is replaced by a single parameter, the crossover scale $r_c$, in DGP. The Supernova redshift observations can be fitted by both models, with $\\Lambda\\sim H_0^2$ and $r_c \\sim H_0^{-1}$. This degeneracy is broken by structure formation, which is suppressed in different ways in the two models. There is some confusion in the literature about how the standard linear growth factor is modified in DGP. While the luminosity distance can be computed purely from the modified 4-dimensional Friedman equation, the evolution of density perturbations requires an analysis of the 5-dimensional gravitational field. We show that if the 5-dimensional effects are inappropriately neglected, then the 4-dimensional Bianchi identities are violated and the computed growth factor is incorrect. By using the 5-dimens...
Scale Factor Self-Dual Cosmological Models
dS, U Camara; Sotkov, G M
2015-01-01
We implement a conformal time scale factor duality for Friedmann-Robertson-Walker cosmological models, which is consistent with the weak energy condition. The requirement for self-duality determines the equations of state for a broad class of barotropic fluids. We study the example of a universe filled with two interacting fluids, presenting an accelerated and a decelerated period, with manifest UV/IR duality. The associated self-dual scalar field interaction turns out to coincide with the "radiation-like" modified Chaplygin gas models. We present an equivalent realization of them as gauged K\\"ahler sigma models (minimally coupled to gravity) with very specific and interrelated K\\"ahler- and super-potentials. Their applications in the description of hilltop inflation and also as quintessence models for the late universe are discussed.
Cosmological Attractor Models and Higher Curvature Supergravity
Cecotti, Sergio
2014-01-01
We study cosmological $\\alpha$-attractors in superconformal/supergravity models, where $\\alpha$ is related to the geometry of the moduli space. For $\\alpha=1$ attractors \\cite{Kallosh:2013hoa} we present a generalization of the previously known manifestly superconformal higher curvature supergravity model \\cite{Cecotti:1987sa}. The relevant standard 2-derivative supergravity with a minimum of two chiral multiplets is shown to be dual to a 4-derivative higher curvature supergravity, where in general one of the chiral superfields is traded for a curvature superfield. There is a degenerate case when both matter superfields become non-dynamical and there is only a chiral curvature superfield, pure higher derivative supergravity. Generic $\\alpha$-models \\cite{Kallosh:2013yoa} interpolate between the attractor point at $\\alpha=0$ and generic chaotic inflation models at large $\\alpha$, in the limit when the inflaton moduli space becomes flat. They have higher derivative duals with the same number of matter fields as...
Holographic, new agegraphic and ghost dark energy models in fractal cosmology
Karami, K; Ghaffari, S; Fahimi, K
2013-01-01
We investigate the holographic, new agegraphic and ghost dark energy models in the framework of fractal cosmology. We consider a fractal FRW universe filled with the dark energy and dark matter. We obtain the equation of state parameters of the selected dark energy models in the ultraviolet regime and discuss on their implications.
Cosmological constraint on Brans-Dicke Model
Li, Ji-Xia; Li, Yi-Chao; Gong, Yan; Chen, Xue-Lei
2015-01-01
We combine new Cosmic Microwave Background (CMB) data from Planck with Baryon Acoustic Oscillation (BAO) data to constrain the Brans-Dicke (BD) theory, in which the gravitational constant $G$ evolves with time. Observations of type Ia supernovae (SNeIa) provide another important set of cosmological data, as they may be regarded as standard candles after some empirical corrections. However, in theories that include modified gravity like the BD theory, there is some risk and complication when using the SNIa data because their luminosity may depend on $G$. In this paper, we assume a power law relation between the SNIa luminosity and $G$, but treat the power index as a free parameter. We then test whether the difference in distances measured with SNIa data and BAO data can be reduced in such a model. We also constrain the BD theory and cosmological parameters by making a global fit with the CMB, BAO and SNIa data set. For the CMB+BAO+SNIa data set, we find $0.08\\times10^{-2} < \\zeta <0.33\\times10^{-2} $ at ...
Preon model and cosmological quantum-hyperchromodynamic phase transition
Nishimura, H.; Hayashi, Y.
1987-05-01
From the cosmological viewpoint, we investigate whether or not recent preon models are compatible with the picture of the first-order phase transition from the preon phase to the composite quark-lepton phase. It is shown that the current models accepting the 't Hooft anomaly-matching condition together with quantum hyperchromodynamics are consistent with the cosmological first-order phase transition.
Cosmological Models with Fractional Derivatives and Fractional Action Functional
Institute of Scientific and Technical Information of China (English)
V.K. Shchigolev
2011-01-01
Cosmological models of a scalar field with dynamical equations containing fractional derivatives or derived from the Einstein-Hilbert action of fractional order, are constructed. A number of exact solutions to those equations of fractional cosmological models in both eases is given.
Implications of the Reduction Principal for Cosmological Natural Selection
Altenberg, Lee
2013-01-01
Smolin (1992) proposed a Darwinian process of universe reproduction - Cosmological Natural Selection - to account for the values of the parameters of the Standard Model. This idea can also be brought to bear on the laws of inheritance proposed to operate during universe production. Universe inheritance laws can themselves evolve within an enlarged state space of universe properties (another recent proposal of Smolin) that includes variation in the transmission laws. This is the strategy introduced by Nei (1967) to understand genetic transmission, through the evolutionary theory of modifier genes, whose methods are adopted here. When mechanisms of variation themselves vary, they are subject to Feldman's (1972) evolutionary Reduction Principle that selection favors greater faithfulness of replication. This dynamic is illustrated with a multitype branching process model of universe creation containing competing inheritance laws. The most faithful inheritance law dominates the ensemble of universes. The Reduction...
Statistics, Computation, and Modeling in Cosmology
Jewell, Jeff; Guiness, Joe; SAMSI 2016 Working Group in Cosmology
2017-01-01
Current and future ground and space based missions are designed to not only detect, but map out with increasing precision, details of the universe in its infancy to the present-day. As a result we are faced with the challenge of analyzing and interpreting observations from a wide variety of instruments to form a coherent view of the universe. Finding solutions to a broad range of challenging inference problems in cosmology is one of the goals of the “Statistics, Computation, and Modeling in Cosmology” workings groups, formed as part of the year long program on ‘Statistical, Mathematical, and Computational Methods for Astronomy’, hosted by the Statistical and Applied Mathematical Sciences Institute (SAMSI), a National Science Foundation funded institute. Two application areas have emerged for focused development in the cosmology working group involving advanced algorithmic implementations of exact Bayesian inference for the Cosmic Microwave Background, and statistical modeling of galaxy formation. The former includes study and development of advanced Markov Chain Monte Carlo algorithms designed to confront challenging inference problems including inference for spatial Gaussian random fields in the presence of sources of galactic emission (an example of a source separation problem). Extending these methods to future redshift survey data probing the nonlinear regime of large scale structure formation is also included in the working group activities. In addition, the working group is also focused on the study of ‘Galacticus’, a galaxy formation model applied to dark matter-only cosmological N-body simulations operating on time-dependent halo merger trees. The working group is interested in calibrating the Galacticus model to match statistics of galaxy survey observations; specifically stellar mass functions, luminosity functions, and color-color diagrams. The group will use subsampling approaches and fractional factorial designs to statistically and
Unified models of the cosmological dark sector
Energy Technology Data Exchange (ETDEWEB)
Zimdahl, W; Velten, H E S [Universidade Federal do EspIrito Santo, Departamento de Fisica, Av. Fernando Ferrari, 514, Campus de Goiabeiras, CEP 29075-910, Vitoria, EspIrito Santo (Brazil); Hipolito-Ricaldi, W S, E-mail: winfried.zimdahl@pq.cnpq.br, E-mail: hipolito@ceunes.ufes.br, E-mail: velten@cce.ufes.br [Universidade Federal do EspIrito Santo, Departamento de Ciencias Matematicas e Naturais, CEUNES Rodovia BR 101 Norte, km. 60, CEP 29932-540, Sao Mateus, Espirito Santo (Brazil)
2011-09-22
We model the cosmological substratum by a viscous fluid that is supposed to provide a unified description of the dark sector and pressureless baryonic matter. In the homogeneous and isotropic background the total energy density of this mixture behaves as a generalized Chaplygin gas. The perturbations of this energy density are intrinsically non-adiabatic and source relative entropy perturbations. The resulting baryonic matter power spectrum is shown to be compatible with the 2dFGRS and SDSS (DR7) data. A joint statistical analysis, using also Hubble-function and supernovae Ia data, shows that, different from other studies, there exists a maximum in the probability distribution for a negative present value q{sub 0} {approx} -0.53 of the deceleration parameter. Moreover, different from other approaches, the unified model presented here favors a matter content that is of the order of the baryonic matter abundance suggested by big-bang nucleosynthesis.
Improving lognormal models for cosmological fields
Xavier, Henrique S; Joachimi, Benjamin
2016-01-01
It is common practice in cosmology to model large-scale structure observables as lognormal random fields, and this approach has been successfully applied in the past to the matter density and weak lensing convergence fields separately. We argue that this approach has fundamental limitations which prevent its use for jointly modelling these two fields since the lognormal distribution's shape can prevent certain correlations to be attainable. Given the need of ongoing and future large-scale structure surveys for fast joint simulations of clustering and weak lensing, we propose two ways of overcoming these limitations. The first approach slightly distorts the power spectra of the fields using one of two algorithms that minimises either the absolute or the fractional distortions. The second one is by obtaining more accurate convergence marginal distributions, for which we provide a fitting function, by integrating the lognormal density along the line of sight. The latter approach also provides a way to determine ...
Introduction to particle cosmology the standard model of cosmology and its open problems
Bambi, Cosimo
2016-01-01
This book introduces the basic concepts of particle cosmology and covers all the main aspects of the Big Bang Model (expansion of the Universe, Big Bang Nucleosynthesis, Cosmic Microwave Background, large scale structures) and the search for new physics (inflation, baryogenesis, dark matter, dark energy). It also includes the majority of recent discoveries, such as the precise determination of cosmological parameters using experiments like WMAP and Planck, the discovery of the Higgs boson at LHC, the non-discovery to date of supersymmetric particles, and the search for the imprint of gravitational waves on the CMB polarization by Planck and BICEP. This textbook is based on the authors’ courses on Cosmology, and aims at introducing Particle Cosmology to senior undergraduate and graduate students. It has been especially written to be accessible even for those students who do not have a strong background in General Relativity and quantum field theory. The content of this book is organized in an easy-to-use ...
Dynamical system approach to running Λ cosmological models
Energy Technology Data Exchange (ETDEWEB)
Stachowski, Aleksander [Jagiellonian University, Astronomical Observatory, Krakow (Poland); Szydlowski, Marek [Jagiellonian University, Astronomical Observatory, Krakow (Poland); Jagiellonian University, Mark Kac Complex Systems Research Centre, Krakow (Poland)
2016-11-15
We study the dynamics of cosmological models with a time dependent cosmological term. We consider five classes of models; two with the non-covariant parametrization of the cosmological term Λ: Λ(H)CDM cosmologies, Λ(a)CDM cosmologies, and three with the covariant parametrization of Λ: Λ(R)CDM cosmologies, where R(t) is the Ricci scalar, Λ(φ)-cosmologies with diffusion, Λ(X)-cosmologies, where X = (1)/(2)g{sup αβ}∇{sub α}∇{sub β}φ is a kinetic part of the density of the scalar field. We also consider the case of an emergent Λ(a) relation obtained from the behaviour of trajectories in a neighbourhood of an invariant submanifold. In the study of the dynamics we used dynamical system methods for investigating how an evolutionary scenario can depend on the choice of special initial conditions. We show that the methods of dynamical systems allow one to investigate all admissible solutions of a running Λ cosmology for all initial conditions. We interpret Alcaniz and Lima's approach as a scaling cosmology. We formulate the idea of an emergent cosmological term derived directly from an approximation of the exact dynamics. We show that some non-covariant parametrization of the cosmological term like Λ(a), Λ(H) gives rise to the non-physical behaviour of trajectories in the phase space. This behaviour disappears if the term Λ(a) is emergent from the covariant parametrization. (orig.)
Non-standard Models and the Sociology of Cosmology
Lopez-Corredoira, Martin
2013-01-01
I review some theoretical ideas in cosmology different from the standard "Big Bang": the quasi-steady state model, the plasma cosmology model, non-cosmological redshifts, alternatives to non-baryonic dark matter and/or dark energy, and others. Cosmologists do not usually work within the framework of alternative cosmologies because they feel that these are not at present as competitive as the standard model. Certainly, they are not so developed, and they are not so developed because cosmologists do not work on them. It is a vicious circle. The fact that most cosmologists do not pay them any attention and only dedicate their research time to the standard model is to a great extent due to a sociological phenomenon (the "snowball effect" or "groupthink"). We might well wonder whether cosmology, our knowledge of the Universe as a whole, is a science like other fields of physics or a predominant ideology.
Non-standard models and the sociology of cosmology
López-Corredoira, Martín
2014-05-01
I review some theoretical ideas in cosmology different from the standard "Big Bang": the quasi-steady state model, the plasma cosmology model, non-cosmological redshifts, alternatives to non-baryonic dark matter and/or dark energy, and others. Cosmologists do not usually work within the framework of alternative cosmologies because they feel that these are not at present as competitive as the standard model. Certainly, they are not so developed, and they are not so developed because cosmologists do not work on them. It is a vicious circle. The fact that most cosmologists do not pay them any attention and only dedicate their research time to the standard model is to a great extent due to a sociological phenomenon (the "snowball effect" or "groupthink"). We might well wonder whether cosmology, our knowledge of the Universe as a whole, is a science like other fields of physics or a predominant ideology.
Experimentally testing the standard cosmological model
Energy Technology Data Exchange (ETDEWEB)
Schramm, D.N. (Chicago Univ., IL (USA) Fermi National Accelerator Lab., Batavia, IL (USA))
1990-11-01
The standard model of cosmology, the big bang, is now being tested and confirmed to remarkable accuracy. Recent high precision measurements relate to the microwave background; and big bang nucleosynthesis. This paper focuses on the latter since that relates more directly to high energy experiments. In particular, the recent LEP (and SLC) results on the number of neutrinos are discussed as a positive laboratory test of the standard cosmology scenario. Discussion is presented on the improved light element observational data as well as the improved neutron lifetime data. alternate nucleosynthesis scenarios of decaying matter or of quark-hadron induced inhomogeneities are discussed. It is shown that when these scenarios are made to fit the observed abundances accurately, the resulting conclusions on the baryonic density relative to the critical density, {Omega}{sub b}, remain approximately the same as in the standard homogeneous case, thus, adding to the robustness of the standard model conclusion that {Omega}{sub b} {approximately} 0.06. This latter point is the deriving force behind the need for non-baryonic dark matter (assuming {Omega}{sub total} = 1) and the need for dark baryonic matter, since {Omega}{sub visible} < {Omega}{sub b}. Recent accelerator constraints on non-baryonic matter are discussed, showing that any massive cold dark matter candidate must now have a mass M{sub x} {approx gt} 20 GeV and an interaction weaker than the Z{sup 0} coupling to a neutrino. It is also noted that recent hints regarding the solar neutrino experiments coupled with the see-saw model for {nu}-masses may imply that the {nu}{sub {tau}} is a good hot dark matter candidate. 73 refs., 5 figs.
Hybrid Models in Loop Quantum Cosmology
Navascués, B Elizaga; Marugán, G A Mena
2016-01-01
In the framework of Loop Quantum Cosmology, inhomogeneous models are usually quantized by means of a hybrid approach that combines loop quantization techniques with standard quantum field theory methods. This approach is based on a splitting of the phase space in a homogeneous sector, formed by global, zero-modes, and an inhomogeneous sector, formed by the remaining, infinite number of modes, that describe the local degrees of freedom. Then, the hybrid quantization is attained by adopting a loop representation for the homogeneous gravitational sector, while a Fock representation is used for the inhomogeneities. The zero-mode of the Hamiltonian constraint operator couples the homogeneous and inhomogeneous sectors. The hybrid approach, therefore, is expected to provide a suitable quantum theory in regimes where the main quantum effects of the geometry are those affecting the zero-modes, while the inhomogeneities, still being quantum, can be treated in a more conventional way. This hybrid strategy was first prop...
Irreversible Processes in Inflationary Cosmological Models
Kremer, G M
2002-01-01
By using the thermodynamic theory of irreversible processes and Einstein general relativity, a cosmological model is proposed where the early universe is considered as a mixture of a scalar field with a matter field. The scalar field refers to the inflaton while the matter field to the classical particles. The irreversibility is related to a particle production process at the expense of the gravitational energy and of the inflaton energy. The particle production process is represented by a non-equilibrium pressure in the energy-momentum tensor. The non-equilibrium pressure is proportional to the Hubble parameter and its proportionality factor is identified with the coefficient of bulk viscosity. The dynamic equations of the inflaton and the Einstein field equations determine the time evolution of the cosmic scale factor, the Hubble parameter, the acceleration and of the energy densities of the inflaton and matter. Among other results it is shown that in some regimes the acceleration is positive which simulate...
Cosmological model in 2d dilaton gravity
Mishima, T; Mishima, Takashi; Nakamichi, Akika
1993-01-01
We apply CGHS-type dilaton gravity model to (1+1)-dimensional cosmological situations. First the behavior of a compact 1-dimensional universe (i.e. like a closed string) is classified on the assumption of homogeneity of universe. Several interesting solutions are found, which include a Misner-type universe having closed time-like curves, and an asymptotically de Sitter universe first pointed out by Yoshimura. In the second half of this talk, we discuss the modification of the classical homogeneous solutions, considering inhomogeneity of classical conformal matters and also quantum back-reaction respectively. (An expanded version of the talk presented by T. Mishima at Yukawa Institute of Theoretical Physics workshop `Quantum Gravity' 24-27, November 1992.)
A Conceptual Tour About the Standard Cosmological Model
Maroto, A L; Maroto, Antonio L.; Ramirez, Juan
2004-01-01
With the beginning of the XXIst century, a physical model of our Universe, usually called the Standard Cosmological Model (SCM), is reaching an important level of consolidation, based on accurate astrophysical data and also on theoretical developments. In this paper we review the interplay between the basic concepts and observations underlying this model. The SCM is a complex and beautiful building, recieving inputs from many branches of physics. Major topics reviewed are: General Relativity and the cosmological constant, the Cosmological Principle and Friedmann-Robertson-Walker-Lemaitre models, Hubble diagrams and dark energy, large scale structure and dark matter, the cosmic microwave background, Big Bang nucleosynthesis, and inflation.
Power law cosmology model comparison with CMB scale information
Tutusaus, Isaac; Blanchard, Alain; Dupays, Arnaud; Zolnierowski, Yves; Cohen-Tanugi, Johann; Ealet, Anne; Escoffier, Stéphanie; Fèvre, Olivier Le; Ilić, Stéphane; Piazza, Federico; Pisani, Alice; Plaszczynski, Stéphane; Sakr, Ziad; Salvatelli, Valentina; Schücker, Thomas; Tilquin, André; Virey, Jean-Marc
2016-01-01
Despite the ability of the cosmological concordance model ($\\Lambda$CDM) to describe the cosmological observations exceedingly well, power law expansion of the Universe scale radius has been proposed as an alternative framework. We examine here these models, analyzing their ability to fit cosmological data using robust model comparison criteria. Type Ia supernovae (SNIa), baryonic acoustic oscillations (BAO) and acoustic scale information from the cosmic microwave background (CMB) have been used. We find that SNIa data either alone or combined with BAO, can be well reproduced by both $\\Lambda$CDM and power law expansion models with $n \\sim 1.5$, while the constant expansion rate model ($n = 1$) is clearly disfavored. Allowing for some redshift evolution in the SNIa luminosity essentially removes any clear preference for a specific model. The CMB data is well known to provide the most stringent constraints on standard cosmological models, in particular through the position of the first peak of the temperature ...
A Monte Carlo Simulation Framework for Testing Cosmological Models
Directory of Open Access Journals (Sweden)
Heymann Y.
2014-10-01
Full Text Available We tested alternative cosmologies using Monte Carlo simulations based on the sam- pling method of the zCosmos galactic survey. The survey encompasses a collection of observable galaxies with respective redshifts that have been obtained for a given spec- troscopic area of the sky. Using a cosmological model, we can convert the redshifts into light-travel times and, by slicing the survey into small redshift buckets, compute a curve of galactic density over time. Because foreground galaxies obstruct the images of more distant galaxies, we simulated the theoretical galactic density curve using an average galactic radius. By comparing the galactic density curves of the simulations with that of the survey, we could assess the cosmologies. We applied the test to the expanding-universe cosmology of de Sitter and to a dichotomous cosmology.
Running vacuum cosmological models: linear scalar perturbations
Perico, E. L. D.; Tamayo, D. A.
2017-08-01
In cosmology, phenomenologically motivated expressions for running vacuum are commonly parameterized as linear functions typically denoted by Λ(H2) or Λ(R). Such models assume an equation of state for the vacuum given by bar PΛ = - bar rhoΛ, relating its background pressure bar PΛ with its mean energy density bar rhoΛ ≡ Λ/8πG. This equation of state suggests that the vacuum dynamics is due to an interaction with the matter content of the universe. Most of the approaches studying the observational impact of these models only consider the interaction between the vacuum and the transient dominant matter component of the universe. We extend such models by assuming that the running vacuum is the sum of independent contributions, namely bar rhoΛ = Σibar rhoΛi. Each Λ i vacuum component is associated and interacting with one of the i matter components in both the background and perturbation levels. We derive the evolution equations for the linear scalar vacuum and matter perturbations in those two scenarios, and identify the running vacuum imprints on the cosmic microwave background anisotropies as well as on the matter power spectrum. In the Λ(H2) scenario the vacuum is coupled with every matter component, whereas the Λ(R) description only leads to a coupling between vacuum and non-relativistic matter, producing different effects on the matter power spectrum.
Particle Physics And Cosmology In Supersymmetric Models
Morrissey, D E
2005-01-01
The Standard Model (SM) of particle physics provides an excellent description of the elementary particle interactions observed in particle collider experiments, but the model does less well when it is applied to cosmology. Recent measurements of the Universe over very large distances indicate the existence of non-luminous dark matter and an excess of baryons over anti-baryons. The SM is unable to account for either of these results, implying that an extension of the SM description is needed. One such extension is supersymmetry. Within the minimal supersymmetric version of the SM, the MSSM, the lightest superpartner particle can make up the dark matter, and the baryon asymmetry can be generated by the mechanism of electroweak baryogenesis (EWBG). In this work, we examine these issues together in order to find out whether the MSSM can account for both of them simultaneously. We find that the MSSM can explain both the baryon asymmetry and the dark matter, but only over a very constrained region of the model para...
Realistic cosmological model with dynamical cancellation of vacuum energy
Dolgov, A D
2003-01-01
We propose a model with a compensating scalar field whose back reaction to the cosmological curvature cancels possible vacuum energy density down to the terms of the order of the time dependent critical energy density. Thus the model simultaneously solves the mystery of the compensation of vacuum energy with the accuracy of 120 orders of magnitude and explains existence of the observed dark energy. At an early stage the suggested cosmological model might experience exponential expansion without an additional inflaton field.
Late time attractors of some varying Chaplygin gas cosmological models
Khurshudyan, M
2015-01-01
Varying Chaplygin gas is one of the dark fluids actively studied in modern cosmology. It does belong to the group of the fluids which has an explicitly given EoS. From the other hand phase space does contain all possible states of the system. Therefore, phase space analysis of the cosmological models does allow to understand qualitative behavior and estimate required characteristics of the models. Phase space analysis is a convenient approach to study a cosmological model, because we do not need to solve a system of differential equations for a given initial conditions, instead, we need to deal with appropriate algebraic equations. The goal of this paper is to find late time attractors for the cosmological models, where a varying Chaplygin gas is one of the components of the large sale universe. We will pay our attention to some non linear interacting models.
Imperfect fluid cosmological model in modified gravity
Samanta, G C
2016-01-01
In this article, we considered the bulk viscous fluid in the formalism of modified gravity in which the general form of a gravitational action is $f(R, T)$ function, where $R$ is the curvature scalar and $T$ is the trace of the energy momentum tensor within the frame of flat FRW space time. The cosmological model dominated by bulk viscous matter with total bulk viscous coefficient expressed as a linear combination of the velocity and acceleration of the expansion of the universe in such a way that $\\xi=\\xi_0+\\xi_1\\frac{\\dot{a}}{a}+\\xi_2\\frac{\\ddot{a}}{\\dot{a}}$, where $\\xi_0$, $\\xi_1$ and $\\xi_2$ are constants. We take $p=(\\gamma-1)\\rho$, where $0\\le\\gamma\\le2$ as an equation of state for perfect fluid. The exact solutions to the corresponding field equations are obtained by assuming a particular model of the form of $f(R, T)=R+2f(T)$, where $f(T)=\\lambda T$, $\\lambda$ is constant. We studied the four possible scenarios for different values of $\\gamma$, such as $\\gamma=0$, $\\gamma=\\frac{2}{3}$, $\\gamma=1$ and...
Testing cosmological models with the Integrated Sachs-Wolfe effect
Energy Technology Data Exchange (ETDEWEB)
Raccanelli, Alvise, E-mail: alvise.raccanelli@port.ac.uk [Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Portsmouth, PO1 3FX (United Kingdom)
2011-02-01
The cross correlation between the Cosmic Microwave Background and the Large Scale Structure of the Universe is a powerful probe to test our cosmological models. This correlation can be used to detect the Integrated Sachs-Wolfe effect, and it depends on both the geometry of the Universe and the properties of the clustering and evolution of structures; for this reason it can be used to test and constrain cosmological models and parameters as well as theories of gravity. In this proceeding we briefly introduce the ISW effect and present some of the recent cosmological tests done using it.
Bianchi-IX string cosmological model in Lyra geometry
Indian Academy of Sciences (India)
F Rahaman; S Chakraborty; N Begum; M Hossain; M Kalam
2003-06-01
A class of cosmological solutions of massive strings for the Bianchi-IX space-time are obtained within the framework of Lyra geometry. Various physical and kinematical properties of the models are discussed.
Field Fractal Cosmological Model As an Example of Practical Cosmology Approach
Baryshev, Yu V
2008-01-01
The idea of the global gravitational effect as the source of cosmological redshift was considered by de Sitter (1916, 1917), Eddington (1923), Tolman (1929) and Bondi (1947), also Hubble (1929) called the discovered distance-redshift relation as "De Sitter effect". For homogeneous matter distribution cosmological gravitational redshift is proportional to square of distance: z_grav ~ r^2. However for a fractal matter distribution having the fractal dimension D=2 the global gravitational redshift is the linear function of distance: z_grav ~ r, which gives possibility for interpretation of the Hubble law without the space expansion. Here the field gravity fractal cosmological model (FGF) is presented, which based on two initial principles. The first assumption is that the field gravity theory describes the gravitational interaction within the conceptual unity of all fundamental physical interactions. The second hypothesis is that the spatial distribution of matter is a fractal at all scales up to the Hubble radi...
An alternative to the cosmological 'concordance model'
Blanchard, A; Rowan-Robinson, M; Sarkar, S; Blanchard, Alain; Douspis, Marian; Rowan-Robinson, Michael; Sarkar, Subir
2003-01-01
Precision measurements of the cosmic microwave background by WMAP are believed to have established a flat Lambda-dominated universe, seeded by nearly scale-invariant adiabatic primordial fluctuations. However by relaxing the hypothesis that the fluctuation spectrum can be described by a single power law, we demonstrate that an Einstein-de Sitter universe with ZERO cosmological constant can fit the data as well as the best concordance model. Moreover unlike a $\\Lambda$-dominated universe, such an universe has no strong integrated Sachs-Wolfe effect, so is in better agreement with the low quadrupole seen by WMAP. The main problem is that the Hubble constant is required to be rather low: H_0 ~ 46 km/s/Mpc; we discuss whether this can be consistent with observations. Furthermore for universes consisting only of baryons and cold dark matter, the amplitude of matter fluctuations on cluster scales is too high, a problem which seems generic. However, an additional small contribution (Omega_X \\sim 0.1) of matter which...
Complementary cosmological tests of RSII brane models
Holanda, R F L; Dahia, F
2013-01-01
In this paper we explore observational bounds on flat and non-flat cosmological models in Type II Randall-Sundrum (RSII) branes. In a first analysis, we consider current measurements of the expansion rate H(z) (with two priors on the local Hubble parameter) and 288 Type Ia supernovae from the Sloan Digital Sky Survey (within the framework of the mlcs2k2 light-curve fitting method). We find that the joint analysis involving these data is an interesting tool to impose limits on the brane tension density parameter (Omega_{lambda}) and that the spatial curvature has a negligible influence on Omega_{lambda} estimates. In order to obtain stronger bounds for the contribution of the $\\Omega_{\\lambda}$ we also add in our analysis the baryon oscillation peak (BAO) and cosmic microwave background radiation (CMB) observations by using the so-called CMB/BAO ratio. From this analysis we find that the Omega_{lambda} contribution is less than 4.10^{-5} (1sigma).
Particle physics and cosmology in supersymmetric models
Morrissey, David Edgar
The Standard Model (SM) of particle physics provides an excellent description of the elementary particle interactions observed in particle collider experiments, but the model does less well when it is applied to cosmology. Recent measurements of the Universe over very large distances indicate the existence of non-luminous dark matter and an excess of baryons over anti-baryons. The SM is unable to account for either of these results, implying that an extension of the SM description is needed. One such extension is supersymmetry. Within the minimal supersymmetric version of the SM, the MSSM, the lightest superpartner particle can make up the dark matter, and the baryon asymmetry can be generated by the mechanism of electroweak baryogenesis (EWBG). In this work, we examine these issues together in order to find out whether the MSSM can account for both of them simultaneously. We find that the MSSM can explain both the baryon asymmetry and the dark matter, but only over a very constrained region of the model parameter space. The strongest constraints on this scenario come from the lower bound on the Higgs boson mass, and the upper bound on the electric dipole moment of the electron. Moreover, upcoming experiments will probe the remaining allowed parameter space in the near future. Some of these constraints may be relaxed by going beyond the MSSM. With this in mind, we also investigate the nMSSM, a minimal singlet extension of the MSSM. We find that this model can also explain both the dark matter and the baryon asymmetry.
A Time-Dependent Λ and G Cosmological Model Consistent with Cosmological Constraints
Directory of Open Access Journals (Sweden)
L. Kantha
2016-01-01
Full Text Available The prevailing constant Λ-G cosmological model agrees with observational evidence including the observed red shift, Big Bang Nucleosynthesis (BBN, and the current rate of acceleration. It assumes that matter contributes 27% to the current density of the universe, with the rest (73% coming from dark energy represented by the Einstein cosmological parameter Λ in the governing Friedmann-Robertson-Walker equations, derived from Einstein’s equations of general relativity. However, the principal problem is the extremely small value of the cosmological parameter (~10−52 m2. Moreover, the dark energy density represented by Λ is presumed to have remained unchanged as the universe expanded by 26 orders of magnitude. Attempts to overcome this deficiency often invoke a variable Λ-G model. Cosmic constraints from action principles require that either both G and Λ remain time-invariant or both vary in time. Here, we propose a variable Λ-G cosmological model consistent with the latest red shift data, the current acceleration rate, and BBN, provided the split between matter and dark energy is 18% and 82%. Λ decreases (Λ~τ-2, where τ is the normalized cosmic time and G increases (G~τn with cosmic time. The model results depend only on the chosen value of Λ at present and in the far future and not directly on G.
Deparametrization and path integral quantization of cosmological models
Simeone, Claudio
2001-01-01
The problem of time is a central feature of quantum cosmology: differing from ordinary quantum mechanics, in cosmology there is nothing "outside" the system which plays the role of clock, and this makes difficult the obtention of a consistent quantization. A possible solution is to assume that a subset of the variables describing the state of the universe can be a clock for the remaining of the system. Following this line, in this book a new proposal consisting in the previous identification of time by means of gauge fixation is applied to the quantization of homogeneous cosmological models. B
Type Ia supernova explosion mechanism and implications for cosmology
Maeda, K.
Type Ia Supernovae (SNe Ia) are believed to be thermonuclear explosions of a white dwarf, and are one of the most mature cosmological standardized candles. However, the explosion mechanism has not yet been fully clarified. Furthermore, they show observational diversities which may be a consequence of either the diversity in the explosion physics and/or surrounding environments, an issue yet to be clarified. In this paper, it is argued that an asymmetry in the explosion is likely a generic feature, and that the diversity arising from various viewing angles can be an origin of observational diversities of SNe Ia seen in their spectral features (suspected possible biases in cosmology) and colors (related to the extinction estimate in cosmology). These findings indicate that at least a part of observational diversities are intrinsic, rather than caused by environment effects, and open up a possibility of using SNe Ia as more precise distance indicators than currently employed.
Tachyon cosmology with non-vanishing minimum potential: a unified model
Energy Technology Data Exchange (ETDEWEB)
Li, Huiquan, E-mail: hqli@ustc.edu.cn [Interdisciplinary Center for Theoretical Study, University of Science and Technology of China, Hefei, Anhui 230026 (China)
2012-07-01
We investigate the tachyon condensation process in the effective theory with non-vanishing minimum potential and its implications to cosmology. It is shown that the tachyon condensation on an unstable three-brane described by this modified tachyon field theory leads to lower-dimensional branes (defects) forming within a stable three-brane. Thus, in the cosmological background, we can get well-behaved tachyon matter after tachyon inflation, (partially) avoiding difficulties encountered in the original tachyon cosmological models. This feature also implies that the tachyon inflated and reheated universe is followed by a Chaplygin gas dark matter and dark energy universe. Hence, such an unstable three-brane behaves quite like our universe, reproducing the key features of the whole evolutionary history of the universe and providing a unified description of inflaton, dark matter and dark energy in a very simple single-scalar field model.
A model for self-tuning the cosmological constant
Kim, J E; Lee, H M; Kim, Jihn E.; Kyae, Bumseok; Lee, Hyun Min
2001-01-01
The vanishing cosmological constant in the four dimensional space-time is obtained in a 5D Randall-Sundrum model with a brane (B1) located at $y=0$. The matter fields can be located at the brane. For settling any vacuum energy generated at the brane to zero, we need a three index antisymmetric tensor field $A_{MNP}$ with a specific form for the Lagrangian. For the self-tuning mechanism, the bulk cosmological constant should be negative.
Dynamical systems and spherically symmetric cosmological models
He, Yanjing
2006-06-01
In this thesis we present a study of the timelike self-similar spherically symmetric cosmological models with two scalar fields with exponential potentials. We first define precisely the timelike self-similar spherically symmetric (TSS) spacetimes. We write the TSS metric in a conformally isometric form in a coordinate system adapted to the geometry of the spacetime manifold. In this coordinate system, both the metric functions of the TSS spacetimes and the potential functions of the scalar fields can be simplified to four undetermined functions of a single coordinate. As a result, the Einstein field equations reduce to an autonomous system of first-order ODEs and polynomial constraints in terms of these undetermined functions. By introducing new bounded variables as well as a new independent variable and solving the constraints, we are able to apply the theory of dynamical systems to study the properties of the TSS solutions. By finding invariant sets and associated monotonic functions, by applying the LaSalle Invariance Principle and the Monotonicity Principle, by applying the [straight phi] t -connected property of a limit set, and using other theorems, we prove that all of the TSS trajectories are heteroclinic trajectories. In addition, we conduct numerical simulations to confirm and support the qualitative analysis. We obtain all possible types of TSS solutions, by analyzing the qualitative behavior of the original system of ODES from those of the reduced one. We obtain asymptotic expressions for the TSS solutions (e.g., the asymptotic expressions for the metric functions, the source functions and the Ricci scalar). In particular, self-similar flat Friedmann-Robertson-Walker spacetimes are examined in order to obtain insights into the issues related to the null surface in general TSS spacetimes in these coordinates. A discussion of the divergence of the spacetime Ricci scalar and the possible extension of the TSS solutions across the null boundary is presented
A New Cosmological Model: Black Hole Universe
Directory of Open Access Journals (Sweden)
Zhang T. X.
2009-07-01
Full Text Available A new cosmological model called black hole universe is proposed. According to this model, the universe originated from a hot star-like black hole with several solar masses, and gradually grew up through a supermassive black hole with billion solar masses to the present state with hundred billion-trillion solar masses by accreting ambient mate- rials and merging with other black holes. The entire space is structured with infinite layers hierarchically. The innermost three layers are the universe that we are living, the outside called mother universe, and the inside star-like and supermassive black holes called child universes. The outermost layer is infinite in radius and limits to zero for both the mass density and absolute temperature. The relationships among all layers or universes can be connected by the universe family tree. Mathematically, the entire space can be represented as a set of all universes. A black hole universe is a subset of the en- tire space or a subspace. The child universes are null sets or empty spaces. All layers or universes are governed by the same physics - the Einstein general theory of relativity with the Robertson-walker metric of spacetime - and tend to expand outward physically. The evolution of the space structure is iterative. When one universe expands out, a new similar universe grows up from its inside. The entire life of a universe begins from the birth as a hot star-like or supermassive black hole, passes through the growth and cools down, and expands to the death with infinite large and zero mass density and absolute temperature. The black hole universe model is consistent with the Mach principle, the observations of the universe, and the Einstein general theory of relativity. Its various aspects can be understood with the well-developed physics without any difficulty. The dark energy is not required for the universe to accelerate its expansion. The inflation is not necessary because the black hole universe
Anisotropic cosmological models in $f (R, T)$ theory of gravitation
Indian Academy of Sciences (India)
Shri Ram; Priyanka; Manish Kumar Singh
2013-07-01
A class of non-singular bouncing cosmological models of a general class of Bianchi models filled with perfect fluid in the framework of $f (R, T)$ gravity is presented. The model initially accelerates for a certain period of time and decelerates thereafter. The physical behaviour of the model is also studied.
Flavor versus mass eigenstates in neutrino asymmetries: implications for cosmology
Barenboim, Gabriela; Kinney, William H.; Park, Wan-Il
2017-09-01
We show that, if they exist, lepton number asymmetries (L_α ) of neutrino flavors should be distinguished from the ones (L_i) of mass eigenstates, since Big Bang Nucleosynthesis (BBN) bounds on the flavor eigenstates cannot be directly applied to the mass eigenstates. Similarly, Cosmic Microwave Background (CMB) constraints on the mass eigenstates do not directly constrain flavor asymmetries. Due to the difference of mass and flavor eigenstates, the cosmological constraint on the asymmetries of neutrino flavors can be much stronger than the conventional expectation, but they are not uniquely determined unless at least the asymmetry of the heaviest neutrino is well constrained. The cosmological constraint on L_i for a specific case is presented as an illustration.
Flavor versus mass eigenstates in neutrino asymmetries: implications for cosmology
Barenboim, Gabriela; Park, Wan-Il
2016-01-01
We show that, if they exist, lepton number asymmetries ($L_\\alpha$) of neutrino flavors should be distinguished from the ones ($L_i$) of mass eigenstates, since Big Bang Nucleosynthesis (BBN) bounds on the flavor eigenstates cannot be directly applied to the mass eigenstates. Similarly, Cosmic Microwave Background (CMB) constraints on mass eigenstates do not directly constrain flavor asymmetries. Due to the difference of mass and flavor eigenstates, the cosmological constraint on the asymmetries of neutrino flavors can be much stronger than conventional expectation, but not uniquely determined unless at least the asymmetry of the heaviest neutrino is well constrained. Cosmological constraint on $L_i$ for a specific case is presented as an illustration.
The evolution of tianxia cosmology and its philosophical implications
Institute of Scientific and Technical Information of China (English)
Liu Junping
2006-01-01
The terminology tianxia has both historical evolution and cultural and philosophical connotations.This concept not only denotes a geographical and spatial meaning,but also implies the moral construct of metaphysics.A systematic study of its historical and cultural repercussions can show that the evolution of the meaning"tianxia"not only embodies the cosmological construction,moral belief and SeIf-identity of the Chinese nation,but also manifests the historical processes of modern China evolving from"tianxia"to a modern nation-state.Meanwhile,the deconstruction of the tianxia cosmology has shattered the old Chinese concept of a single united tianxia,or the whole world under one Heaven.Also,"Confucian China"has been increasingly losing its vitality and strong hold on the people,while the concept of nation-state has gained its way into people's consciousness,which has added more diversity and open-mindedness to the concept of tianxia.
Cosmological Implications of Trace-Charged Dark Matter
Morgan, Jason P
2016-01-01
Trace charge imbalances can explain puzzling cosmological observations such as the large `missing' fraction of electrons in cosmic rays and their contrast to the charge-neutral solar wind, the extreme energy sources that sustain quasars, galactic jets, and active galactic nuclei, the origin and nature of `dark matter' galaxy haloes, and the apparent acceleration of the expansion of the Universe, obviating $\\Lambda$CDM. When there are $\\sim \
Cosmological Model Based on Gauge Theory of Gravity
Institute of Scientific and Technical Information of China (English)
WU Ning
2005-01-01
A cosmological model based on gauge theory of gravity is proposed in this paper. Combining cosmological principle and field equation of gravitational gauge field, dynamical equations of the scale factor R(t) of our universe can be obtained. This set of equations has three different solutions. A prediction of the present model is that, if the energy density of the universe is not zero and the universe is expanding, the universe must be space-flat, the total energy density must be the critical density ρc of the universe. For space-flat case, this model gives the same solution as that of the Friedmann model. In other words, though they have different dynamics of gravitational interactions, general relativity and gauge theory of gravity give the same cosmological model.
Five-Dimensional Cosmological Model with Variable G and Λ
Institute of Scientific and Technical Information of China (English)
H. Baysal; (I). Yilmaz
2007-01-01
@@ Einstein's field equations with G and Λ both varying with time are considered in the presence of a perfect fluid for five-dimensional cosmological model in a way which conserves the energy momentum tensor of the matter content. Several sets of explicit solutions in the five-dimensional Kaluza-Klein type cosmological models with variable G and Λ are obtained. The diminishment of extra dimension with the evolution of the universe for the five-dimensional model is exhibited. The physical properties of the models are examined.
A New Type of Isotropic Cosmological Model
Naboulsi, R
2003-01-01
The Einstein equations with quantum one-loop contributions of conformally covariant matter fields in the poresence of frac{1}{t^2} decaying matter density and decaying cosmological constant is used to study an isotropic homogenous FRW space-time. We show that scale factor depends on the sums of contributions from quantum fields with different spin values. For some specific values of this later, the Universe could be in an accelerated regime.
Cosmological and astrophysical constraints on tachyon dark energy models
Martins, C J A P
2016-01-01
Rolling tachyon field models are among the candidates suggested as explanations for the recent acceleration of the Universe. In these models the field is expected to interact with gauge fields and lead to variations of the fine-structure constant $\\alpha$. Here we take advantage of recent observational progress and use a combination of background cosmological observations of Type Ia supernovas and astrophysical and local measurements of $\\alpha$ to improve constraints on this class of models. We show that the constraints on $\\alpha$ imply that the field dynamics must be extremely slow, leading to a constraint of the present-day dark energy equation of state $(1+w_0)<2.4\\times10^{-7}$ at the $99.7\\%$ confidence level. Therefore current and forthcoming standard background cosmology observational probes can't distinguish this class of models from a cosmological constant, while detections of $\\alpha$ variations could possibly do so since they would have a characteristic redshift dependence.
Cosmological and astrophysical constraints on tachyon dark energy models
Martins, C. J. A. P.; Moucherek, F. M. O.
2016-06-01
Rolling tachyon field models are among the candidates suggested as explanations for the recent acceleration of the Universe. In these models the field is expected to interact with gauge fields and lead to variations of the fine-structure constant α . Here we take advantage of recent observational progress and use a combination of background cosmological observations of type Ia supernovas and astrophysical and local measurements of α to improve constraints on this class of models. We show that the constraints on α imply that the field dynamics must be extremely slow, leading to a constraint of the present-day dark energy equation of state (1 +w0)<2.4 ×10-7 at the 99.7% confidence level. Therefore current and forthcoming standard background cosmology observational probes cannot distinguish this class of models from a cosmological constant, while detections of α variations could possibly do so since they would have a characteristic redshift dependence.
Decaying Domain Walls in an Extended Gravity Model and Cosmology
Shiraishi, Kiyoshi
2013-01-01
We investigate cosmological consequences of an extended gravity model which belongs to the same class studied by Accetta and Steinhardt in an extended inflationary scenario. But we do not worry about inflation in our model; instead, we focus on a topological object formed during cosmological phase transitions. Although domain walls appear during first-order phase transitions such as QCD transition, they decay at the end of the phase transition. Therefore the "domain wall problem" does not exist in the suitable range of pameters and, on the contrary, the "fragments" of walls may become seeds of dark matter. A possible connection to "oscillating universe" model offered by Morikawa et al. is also discussed.
Grieb, Jan Niklas; Salazar-Albornoz, Salvador; Scoccimarro, Román; Crocce, Martín; Vecchia, Claudio Dalla; Montesano, Francesco; Gil-Marín, Héctor; Ross, Ashley J; Beutler, Florian; Rodríguez-Torres, Sergio; Chuang, Chia-Hsun; Prada, Francisco; Kitaura, Francisco-Shu; Cuesta, Antonio J; Eisenstein, Daniel J; Percival, Will J; Vargas-Magana, Mariana; Tinker, Jeremy L; Tojeiro, Rita; Brownstein, Joel R; Maraston, Claudia; Nichol, Robert C; Olmstead, Matthew D; Samushia, Lado; Seo, Hee-Jong; Streblyanska, Alina; Zhao, Gong-bo
2016-01-01
We extract cosmological information from the anisotropic power spectrum measurements from the recently completed Baryon Oscillation Spectroscopic Survey (BOSS), extending the concept of clustering wedges to Fourier space. Making use of new FFT-based estimators, we measure the power spectrum clustering wedges of the BOSS sample by filtering out the information of Legendre multipoles l > 4. Our modelling of these measurements is based on novel approaches to describe non-linear evolution, bias, and redshift-space distortions, which we test using synthetic catalogues based on large-volume N-body simulations. We are able to include smaller scales than in previous analyses, resulting in tighter cosmological constraints. Using three overlapping redshift bins, we measure the angular diameter distance, the Hubble parameter, and the cosmic growth rate, and explore the cosmological implications of our full shape clustering measurements in combination with CMB and SN Ia data. Assuming a {\\Lambda}CDM cosmology, we constra...
The Cluster Mass Function from Early SDSS Data: Cosmological Implications
Bahcall, Neta A.; Dong, Feng; Bode, Paul; Kim, Rita; Annis, James; Mckay, Timothy A.; Hansen, Sarah; Gunn, James; Ostriker, Jeremiah P.; Postman, Marc; Nichol, Robert C.; Goto, Tomotsugu; Brinkmann, Jon; Knapp, Gillian R.; Lamb, Don O.
2002-01-01
The mass function of clusters of galaxies is determined from 400 deg^2 of early commissioning imaging data of the Sloan Digital Sky Survey; ~300 clusters in the redshift range z = 0.1 - 0.2 are used. Clusters are selected using two independent selection methods: a Matched Filter and a red-sequence color magnitude technique. The two methods yield consistent results. The cluster mass function is compared with large-scale cosmological simulations. We find a best-fit cluster normalization relatio...
Implications of a positive cosmological constant for general relativity.
Ashtekar, Abhay
2017-08-29
Most of the literature on general relativity over the last century assumes that the cosmological constant [Formula: see text] is zero. However, by now independent observations have led to a consensus that the dynamics of the universe is best described by Einstein's equations with a small but positive [Formula: see text]. Interestingly, this requires a drastic revision of conceptual frameworks commonly used in general relativity, no matter how small [Formula: see text] is. We first explain why, and then summarize the current status of generalizations of these frameworks to include a positive [Formula: see text], focusing on gravitational waves.
Energy Technology Data Exchange (ETDEWEB)
1992-09-01
The bibliography contains citations concerning the use of superstrings in studies of such relativistic phenomena as space-time extension and supergravity. Primordial magnetic monopoles, local cosmic strings, and studies of preon models are among the topics discussed. Calbi-Yau manifolds, and supersymmetrical Kaluza-Klein theories are also considered. Citations relating specifically to particle studies are included in a separate bibliography. (Contains a minimum of 103 citations and includes a subject term index and title list.)
Cosmological constraints on spontaneous R-symmetry breaking models
Energy Technology Data Exchange (ETDEWEB)
Hamada, Yuta; Kobayashi, Tatsuo [Kyoto Univ. (Japan). Dept. of Physics; Kamada, Kohei [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Ookouchi, Yutaka [Kyoto Univ. (Japan). Dept. of Physics; Kyoto Univ. (Japan). The Hakubi Center for Advanced Research and Dept. of Physics
2012-11-15
We study general constraints on spontaneous R-symmetry breaking models coming from the cosmological effects of the pseudo Nambu-Goldstone bosons, R-axions. They are substantially produced in the early Universe and may cause several cosmological problems. We focus on relatively long-lived R-axions and find that in a wide range of parameter space, models are severely constrained. In particular, R-axions with mass less than 1 MeV are generally ruled out for relatively high reheating temperature, T{sub R}>10 GeV.
Hmong Cosmology: Proposed Model, Preliminary Insights
Directory of Open Access Journals (Sweden)
Vincent K. Her
2006-01-01
Full Text Available Is there an underlying structure to Hmong cosmology? What are its components? And how might these interrelate? In this paper, I will show that the Hmong cosmos consists of three separate realms and that these are connected together by the cycle of the human soul. Using zaaj qhuabke, I will trace the journey of the deceased and look at how ritual movement is expressive of human agency, narrative experience and community history. My insights are based on primary fieldwork research carried out for a doctoral dissertation on Hmong funeral rites in the Midwest.
Bianchi type IX string cosmological model in general relativity
Indian Academy of Sciences (India)
Raj Bali; Shuchi Dave
2001-04-01
We have investigated Bianchi type IX string cosmological models in general relativity. To get a determinate solution, we have assumed a condition ρ= i.e. rest energy density for a cloud of strings is equal to the string tension density. The various physical and geometrical aspects of the models are also discussed.
Axially Symmetric Cosmological Mesonic Stiff Fluid Models in Lyra's Geometry
Gad, Ragab M
2009-01-01
In this paper, we obtained a new class of axially symmetric cosmological mesonic stiff fluid models in the context of Lyra's geometry. Expressions for the energy, pressure and the massless scalar field are derived by considering the time dependent displacement field. We found that the mesonic scalar field depends on only $t$ coordinate. Some physical properties of the obtained models are discussed.
Physical Models of Galaxy Formation in a Cosmological Framework
Somerville, Rachel S.; Davé, Romeel
2015-08-01
Modeling galaxy formation in a cosmological context presents one of the greatest challenges in astrophysics today due to the vast range of scales and numerous physical processes involved. Here we review the current status of models that employ two leading techniques to simulate the physics of galaxy formation: semianalytic models and numerical hydrodynamic simulations. We focus on a set of observational targets that describe the evolution of the global and structural properties of galaxies from roughly cosmic high noon (z â¼ 2-3) to the present. Although minor discrepancies remain, overall, models show remarkable convergence among different methods and make predictions that are in qualitative agreement with observations. Modelers have converged on a core set of physical processes that are critical for shaping galaxy properties. This core set includes cosmological accretion, strong stellar-driven winds that are more efficient at low masses, black hole feedback that preferentially suppresses star formation at high masses, and structural and morphological evolution through merging and environmental processes. However, all cosmological models currently adopt phenomenological implementations of many of these core processes, which must be tuned to observations. Many details of how these diverse processes interact within a hierarchical structure formation setting remain poorly understood. Emerging multiscale simulations are helping to bridge the gap between stellar and cosmological scales, placing models on a firmer, more physically grounded footing. Concurrently, upcoming telescope facilities will provide new challenges and constraints for models, particularly by directly constraining inflows and outflows through observations of gas in and around galaxies.
Pulse-wise GRB correlation: implication as a cosmological tool
Basak, Rupal
2016-01-01
Gamma-ray bursts (GRBs) are cosmological explosions which carry valuable information from the distant past of the expanding universe. One of the greatest discoveries in modern cosmology is the finding of the accelerated expansion of the universe using Type Ia supernovae (SN Ia) as standard candles. However, due to the interstellar extinction SN Ia can be seen only up to a redshift $z\\sim 1.5$. GRBs are considered as the potential alternative to push this limit to as high as $z\\sim 10$, a redshift regime corresponding to an epoch when the universe just started to form the first structures. There exist several correlations between the energy and an observable of a GRB which can be used to derive luminosity distance. In recent works, we have studied spectral evolution within the individual pulses and obtained such correlations within the pulses. Here we summarize our results of the pulse-wise GRB correlation study. It is worth mentioning that all GRB correlations are still empirical, and we cannot use them in co...
Exactly solvable model for cosmological perturbations in dilatonic brane worlds
Koyama, K; Koyama, Kazuya; Takahashi, Keitaro
2003-01-01
We construct a model where cosmological perturbations are analytically solved based on dilatonic brane worlds. A bulk scalar field has an exponential potential in the bulk and an exponential coupling to the brane tension. The bulk scalar field yields a power-law inflation on the brane. The exact background metric can be found including the back-reaction of the scalar field. Then exact solutions for cosmological perturbations which properly satisfy the junction conditions on the brane are derived. These solutions provide us an interesting model to understand the connection between the behavior of cosmological perturbations on the brane and the geometry of the bulk. Using these solutions, the behavior of an anisotropic stress induced on the inflationary brane by bulk gravitational fields is investigated.
Power law cosmology model comparison with CMB scale information
Tutusaus, Isaac; Lamine, Brahim; Blanchard, Alain; Dupays, Arnaud; Zolnierowski, Yves; Cohen-Tanugi, Johann; Ealet, Anne; Escoffier, Stéphanie; Le Fèvre, Olivier; Ilić, Stéphane; Pisani, Alice; Plaszczynski, Stéphane; Sakr, Ziad; Salvatelli, Valentina; Schücker, Thomas; Tilquin, André; Virey, Jean-Marc
2016-11-01
Despite the ability of the cosmological concordance model (Λ CDM ) to describe the cosmological observations exceedingly well, power law expansion of the Universe scale radius, R (t )∝tn, has been proposed as an alternative framework. We examine here these models, analyzing their ability to fit cosmological data using robust model comparison criteria. Type Ia supernovae (SNIa), baryonic acoustic oscillations (BAO) and acoustic scale information from the cosmic microwave background (CMB) have been used. We find that SNIa data either alone or combined with BAO can be well reproduced by both Λ CDM and power law expansion models with n ˜1.5 , while the constant expansion rate model (n =1 ) is clearly disfavored. Allowing for some redshift evolution in the SNIa luminosity essentially removes any clear preference for a specific model. The CMB data are well known to provide the most stringent constraints on standard cosmological models, in particular, through the position of the first peak of the temperature angular power spectrum, corresponding to the sound horizon at recombination, a scale physically related to the BAO scale. Models with n ≥1 lead to a divergence of the sound horizon and do not naturally provide the relevant scales for the BAO and the CMB. We retain an empirical footing to overcome this issue: we let the data choose the preferred values for these scales, while we recompute the ionization history in power law models, to obtain the distance to the CMB. In doing so, we find that the scale coming from the BAO data is not consistent with the observed position of the first peak of the CMB temperature angular power spectrum for any power law cosmology. Therefore, we conclude that when the three standard probes (SNIa, BAO, and CMB) are combined, the Λ CDM model is very strongly favored over any of these alternative models, which are then essentially ruled out.
Integrable Cosmological Models From Higher Dimensional Einstein Equations
Sano, M; Sano, Masakazu; Suzuki, Hisao
2007-01-01
We consider the cosmological models for the higher dimensional spacetime which includes the curvatures of our space as well as the curvatures of the internal space. We find that the condition for the integrability of the cosmological equations is that the total space-time dimensions are D=10 or D=11 which is exactly the conditions for superstrings or M-theory. We obtain analytic solutions with generic initial conditions in the four dimensional Einstein frame and study the accelerating universe when both our space and the internal space have negative curvatures.
Scale invariant cosmology II: model equations and properties
Maeder, Andre
2016-01-01
We want to establish the basic properties of a scale invariant cosmology, that also accounts for the hypothesis of scale invariance of the empty space at large scales. We write the basic analytical properties of the scale invariant cosmological models. The hypothesis of scale invariance of the empty space at large scale brings interesting simplifications in the scale invariant equations for cosmology. There is one new term, depending on the scale factor of the scale invariant cosmology, that opposes to gravity and favours an accelerated expansion. We first consider a zero-density model and find an accelerated expansion, going like t square. In models with matter present, the displacements due to the new term make a significant contribution Omega_l to the energy-density of the Universe, satisfying an equation of the form Omega_m + Omega_k + Omega_l = 1. Unlike the Friedman's models, there is a whole family of flat models (k=0) with different density parameters Omega_m smaller than 1. We examine the basic relat...
Emergent universe in spatially flat cosmological model
Zhang, Kaituo; Yu, Hongwei
2013-01-01
The scenario of an emergent universe provides a promising resolution to the big bang singularity in universes with positive or negative spatial curvature. It however remains unclear whether the scenario can be successfully implemented in a spatially flat universe which seems to be favored by present cosmological observations. In this paper, we study the stability of Einstein static state solutions in a spatially flat Shtanov-Sahni braneworld scenario. With a negative dark radiation term included and assuming a scalar field as the only matter energy component, we find that the universe can stay at an Einstein static state past eternally and then evolve to an inflation phase naturally as the scalar field climbs up its potential slowly. In addition, we also propose a concrete potential of the scalar field that realizes this scenario.
Anisotropic cosmological models and generalized scalar tensor theory
Indian Academy of Sciences (India)
Subenoy Chakraborty; Batul Chandra Santra; Nabajit Chakravarty
2003-10-01
In this paper generalized scalar tensor theory has been considered in the background of anisotropic cosmological models, namely, axially symmetric Bianchi-I, Bianchi-III and Kortowski–Sachs space-time. For bulk viscous ﬂuid, both exponential and power-law solutions have been studied and some assumptions among the physical parameters and solutions have been discussed.
Testing Cosmological Models with Type Ic Super Luminous Supernovae
Wei, Jun-Jie; Melia, Fulvio
2015-01-01
The use of type Ic Super Luminous Supernovae (SLSN Ic) to examine the cosmological expansion introduces a new standard ruler with which to test theoretical models. The sample suitable for this kind of work now includes 11 SLSNe Ic, which have thus far been used solely in tests involving $\\Lambda$CDM. In this paper, we broaden the base of support for this new, important cosmic probe by using these observations to carry out a one-on-one comparison between the $R_{\\rm h}=ct$ and $\\Lambda$CDM cosmologies. We individually optimize the parameters in each cosmological model by minimizing the $\\chi^{2}$ statistic. We also carry out Monte Carlo simulations based on these current SLSN Ic measurements to estimate how large the sample would have to be in order to rule out either model at a $\\sim 99.7\\%$ confidence level. The currently available sample indicates a likelihood of $\\sim$$70-80\\%$ that the $R_{\\rm h}=ct$ Universe is the correct cosmology versus $\\sim$$20-30\\%$ for the standard model. These results are suggest...
Salazar-Albornoz, Salvador; Grieb, Jan Niklas; Crocce, Martin; Scoccimarro, Roman; Alam, Shadab; Beutler, Florian; Brownstein, Joel R; Chuang, Chia-Hsun; Kitaura, Francisco-Shu; Olmstead, Matthew D; Percival, Will J; Prada, Francisco; Rodríguez-Torres, Sergio; Samushia, Lado; Tinker, Jeremy; Thomas, Daniel; Tojeiro, Rita; Wang, Yuting; Zhao, Gong-bo
2016-01-01
We investigate the cosmological implications of studying galaxy clustering using a tomographic approach applied to the final BOSS DR12 galaxy sample, including both auto- and cross-correlation functions between redshift shells. We model the signal of the full shape of the angular correlation function, $\\omega(\\theta)$, in redshift bins using state-of-the-art modelling of non-linearities, bias and redshift-space distortions. We present results on the redshift evolution of the linear bias of BOSS galaxies, which cannot be obtained with traditional methods for galaxy-clustering analysis. We also obtain constraints on cosmological parameters, combining this tomographic analysis with measurements of the cosmic microwave background (CMB) and type Ia supernova (SNIa). We explore a number of cosmological models, including the standard $\\Lambda$CDM model and its most interesting extensions, such as deviations from $w_\\rm{DE} = -1$, non-minimal neutrino masses, spatial curvature and deviations from general relativity u...
Investigating inhomogeneous Szekeres models and their applications to precision cosmology
Peel, Austin Chandler
Exact solutions of Einstein's field equations that can describe the evolution of complex structures in the universe provide complementary frameworks to standard perturbation theory in which to analyze cosmological and astrophysical phenomena. The flexibility and generality of the inhomogeneous and anisotropic Szekeres metric make it the best known exact solution to explore nonlinearities in the universe. We study applications of Szekeres models to precision cosmology, focusing on the influence of inhomogeneities in two primary contexts---the growth rate of cosmic structures and biases in distance determinations to remote sources. We first define and derive evolution equations for a Szekeres density contrast, which quantifies exact deviations from a smooth background cosmology. Solving these equations and comparing to the usual perturbative approach, we find that for models with the same matter content, the Szekeres growth rate is larger through the matter-dominated cosmic era. Including a cosmological constant, we consider exact global perturbations, as well as the evolution of a single extended structure surrounded by an almost homogeneous background. For the former, we use growth data to obtain a best fit Szekeres model and find that it can fit the data as well as the standard Lambda-Cold Dark Matter (LCDM) cosmological model but with different cosmological parameters. Next, to study effects of inhomogeneities on distance measures, we build an exact relativistic Swiss-cheese model of the universe, where a large number of non-symmetric and randomly placed Szekeres structures are embedded within a LCDM background. Solving the full relativistic propagation equations, light beams are traced through the model, where they traverse the inhomogeneous structures in a way that mimics the paths of real light beams in the universe. For beams crossing a single structure, their magnification or demagnification reflects primarily the net density encountered along the path
Pairwise velocities in the "Running FLRW" cosmological model
Bibiano, Antonio; Croton, Darren J.
2017-01-01
We present an analysis of the pairwise velocity statistics from a suite of cosmological N-body simulations describing the "Running Friedmann-Lemaître-Robertson-Walker" (R-FLRW) cosmological model. This model is based on quantum field theory in a curved space-time and extends ΛCDM with a time-evolving vacuum energy density, ρ _Λ. To enforce local conservation of matter a time-evolving gravitational coupling is also included. Our results constitute the first study of velocities in the R-FLRW cosmology, and we also compare with other dark energy simulations suites, repeating the same analysis. We find a strong degeneracy between the pairwise velocity and σ8 at z = 0 for almost all scenarios considered, which remains even when we look back to epochs as early as z = 2. We also investigate various Coupled Dark Energy models, some of which show minimal degeneracy, and reveal interesting deviations from ΛCDM which could be readily exploited by future cosmological observations to test and further constrain our understanding of dark energy.
Dark-energy cosmological models in f( G) gravity
Shamir, M. F.
2016-10-01
We discuss dark-energy cosmological models in f( G) gravity. For this purpose, a locally rotationally symmetric Bianchi type I cosmological model is considered. First, exact solutions with a well-known form of the f( G) model are explored. One general solution is discussed using a power-law f( G) gravity model and physical quantities are calculated. In particular, Kasner's universe is recovered and the corresponding f( G) gravity models are reported. Second, the energy conditions for the model under consideration are discussed using graphical analysis. It is concluded that solutions with f( G) = G 5/6 support expansion of universe while those with f( G) = G 1/2 do not favor the current expansion.
A cosmological model in Weyl-Cartan spacetime
Puetzfeld, D; Puetzfeld, Dirk; Tresguerres, Romualdo
2001-01-01
We present a cosmological model for early stages of the universe on the basis of a Weyl-Cartan spacetime. In this model, torsion $T^{\\alpha}$ and nonmetricity $Q_{\\alpha \\beta}$ are proportional to the vacuum polarization. Extending earlier work of Tresguerres, we discuss the behaviour of the cosmic scale factor and the Weyl 1-form in detail. We show how our model fits into the more general framework of metric-affine gravity (MAG).
Magnetized cosmological models in bimetric theory of gravitation
Indian Academy of Sciences (India)
S D Katore; R S Rane
2006-08-01
Bianchi type-III magnetized cosmological model when the field of gravitation is governed by either a perfect fluid or cosmic string is investigated in Rosen's [1] bimetric theory of gravitation. To complete determinate solution, the condition, viz., = (), where is a constant, between the metric potentials is used. We have assumed different equations of state for cosmic string [2] for the complete solution of the model. Some physical and geometrical properties of the exhibited model are discussed and studied.
Physical Models of Galaxy Formation in a Cosmological Framework
Somerville, Rachel S.; Davé, Romeel
2014-01-01
Modeling galaxy formation in a cosmological context presents one of the greatest challenges in astrophysics today, due to the vast range of scales and numerous physical processes involved. Here we review the current status of models that employ two leading techniques to simulate the physics of galaxy formation: semi-analytic models and numerical hydrodynamic simulations. We focus on a set of observational targets that describe the evolution of the global and structural properties of galaxies ...
Cosmological Models with Variable Deceleration Parameter in Lyra's Manifold
Pradhan, A; Singh, C B
2006-01-01
FRW models of the universe have been studied in the cosmological theory based on Lyra's manifold. A new class of exact solutions has been obtained by considering a time dependent displacement field for variable deceleration parameter from which three models of the universe are derived (i) exponential (ii) polynomial and (iii) sinusoidal form respectively. The behaviour of these models of the universe are also discussed. Finally some possibilities of further problems and their investigations have been pointed out.
The models of cosmological inflation in the context of kinetic approximation
Fomin, I.
2016-07-01
In this work the building of models of cosmological inflation with approximate linear dependence of the scalar field kinetic energy on the state parameter is considered. The key parameters of cosmological perturbations are also calculated.
Physical Models of Galaxy Formation in a Cosmological Framework
Somerville, Rachel S
2014-01-01
Modeling galaxy formation in a cosmological context presents one of the greatest challenges in astrophysics today, due to the vast range of scales and numerous physical processes involved. Here we review the current status of models that employ two leading techniques to simulate the physics of galaxy formation: semi-analytic models and numerical hydrodynamic simulations. We focus on a set of observational targets that describe the evolution of the global and structural properties of galaxies from roughly Cosmic High Noon ($z\\sim 2-3$) to the present. Although minor discrepancies remain, overall, models show remarkable convergence between different methods and make predictions that are in qualitative agreement with observations. Modelers seem to have converged on a core set of physical processes that are critical for shaping galaxy properties. This core set includes cosmological accretion, strong stellar-driven winds that are more efficient at low masses, black hole feedback that preferentially suppresses star...
Early universe cosmology. In supersymmetric extensions of the standard model
Energy Technology Data Exchange (ETDEWEB)
Baumann, Jochen Peter
2012-03-19
In this thesis we investigate possible connections between cosmological inflation and leptogenesis on the one side and particle physics on the other side. We work in supersymmetric extensions of the Standard Model. A key role is played by the right-handed sneutrino, the superpartner of the right-handed neutrino involved in the type I seesaw mechanism. We study a combined model of inflation and non-thermal leptogenesis that is a simple extension of the Minimal Supersymmetric Standard Model (MSSM) with conserved R-parity, where we add three right-handed neutrino super fields. The inflaton direction is given by the imaginary components of the corresponding scalar component fields, which are protected from the supergravity (SUGRA) {eta}-problem by a shift symmetry in the Kaehler potential. We discuss the model first in a globally supersymmetric (SUSY) and then in a supergravity context and compute the inflationary predictions of the model. We also study reheating and non-thermal leptogenesis in this model. A numerical simulation shows that shortly after the waterfall phase transition that ends inflation, the universe is dominated by right-handed sneutrinos and their out-of-equilibrium decay can produce the desired matter-antimatter asymmetry. Using a simplified time-averaged description, we derive analytical expressions for the model predictions. Combining the results from inflation and leptogenesis allows us to constrain the allowed parameter space from two different directions, with implications for low energy neutrino physics. As a second thread of investigation, we discuss a generalisation of the inflationary model discussed above to include gauge non-singlet fields as inflatons. This is motivated by the fact that in left-right symmetric, supersymmetric Grand Unified Theories (SUSY GUTs), like SUSY Pati-Salam unification or SUSY SO(10) GUTs, the righthanded (s)neutrino is an indispensable ingredient and does not have to be put in by hand as in the MSSM. We discuss
Evolution of Interacting Viscous Dark Energy Model in Einstein Cosmology
Institute of Scientific and Technical Information of China (English)
CHEN Ju-Hua; ZHOU Sheng; WANG Yong-Jiu
2011-01-01
We investigate the evolution of the viscous dark energy (DE) interacting with the dark matter (DM) in the Einstein cosmology model. By using the linearizing theory of the dynamical system, we find that, in our model,there exists a stable late time scaling solution which corresponds to the accelerating universe. We also find the unstable solution under some appropriate parameters. In order to alleviate the coincidence problem, some authors considered the effect of quantum correction due to the conform anomaly and the interacting dark energy with the dark matter. However, if we take into account the bulk viscosity of the cosmic fluid, the coincidence problem will be softened just like the interacting dark energy cosmology model. That is to say, both the non-perfect fluid model and the interacting the dark energy cosmic model can alleviate or soften the singularity of the universe.%@@ We investigate the evolution of the viscous dark energy (DE) interacting with the dark matter (DM) in the Einstein cosmology model.By using the linearizing theory of the dynamical system, we find that, in our model, there exists a stable late time scaling solution which corresponds to the accelerating universe.We also find the unstable solution under some appropriate parameters.In order to alleviate the coincidence problem, some authors considered the effect of quantum correction due to the conform anomaly and the interacting dark energy with the dark matter.However, if we take into account the bulk viscosity of the cosmic fluid, the coincidence problem will be softened just like the interacting dark energy cosmology model.That is to say, both the non-perfect fluid model and the interacting the dark energy cosmic model can alleviate or soften the singularity of the universe.
Cosmological dynamics of a class of non-minimally coupled models of gravity
Azevedo, R P L
2016-01-01
In this work a new non-minimally coupled model is presented, where a generic function $f(R)$ of the scalar curvature factors the usual Einstein-Hilbert action functional, motivated by relevant results obtained from similar models. Its cosmological dynamics are derived and the possibility of attaining a phase of accelerated expansion is assessed. To further probe the possible implications of the model, a dynamical system formulation is established, and used to assess the scenarios where $f(R)$ assumes a power-law or exponential form.
Cosmological viability conditions for f(T) dark energy models
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)
2012-11-01
Recently f(T) modified teleparallel gravity where T is the torsion scalar has been proposed as the natural gravitational alternative for dark energy. We perform a detailed dynamical analysis of these models and find conditions for the cosmological viability of f(T) dark energy models as geometrical constraints on the derivatives of these models. We show that in the phase space exists two cosmologically viable trajectory which (i) The universe would start from an unstable radiation point, then pass a saddle standard matter point which is followed by accelerated expansion de sitter point. (ii) The universe starts from a saddle radiation epoch, then falls onto the stable matter era and the system can not evolve to the dark energy dominated epoch. Finally, for a number of f(T) dark energy models were proposed in the more literature, the viability conditions are investigated.
The GRBs Hubble diagram in quintessential cosmological models
Demianski, Marek; Rubano, Claudio
2010-01-01
It has been recently empirically established that some of the directly observed pa- rameters of GRBs are correlated with their important intrinsic parameters, like the luminosity or the total radiated energy. These correlations were derived, tested and used to standardize GRBs, i.e., to derive their luminosity or radiated energy from one or more observables, in order to construct an estimated fiducial Hubble diagram, assuming that radiation propagates in the standard LambdaCDM cosmological model. We extend these analyses by considering more general models of dark energy, and an updated data set of high redshift GRBs. We show that the correlation parameters only weakly depend on the cosmological model. Moreover we apply a local regression technique to estimate, in a model independent way, the distance modulus from the recently updated SNIa sample containing 307 SNIa (Astier et al. 2006), in order to calibrate the GRBs 2D correlations, considering only GRBs with z <1.4. The derived calibration parameters are...
Viscous dissipative Chaplygin gas dominated homogenous and isotropic cosmological models
Pun, C S J; Mak, M K; Kovács, Z; Szabó, G M; Harko, T
2008-01-01
The generalized Chaplygin gas, which interpolates between a high density relativistic era and a non-relativistic matter phase, is a popular dark energy candidate. We consider a generalization of the Chaplygin gas model, by assuming the presence of a bulk viscous type dissipative term in the effective thermodynamic pressure of the gas. The dissipative effects are described by using the truncated Israel-Stewart model, with the bulk viscosity coefficient and the relaxation time functions of the energy density only. The corresponding cosmological dynamics of the bulk viscous Chaplygin gas dominated universe is considered in detail for a flat homogeneous isotropic Friedmann-Robertson-Walker geometry. For different values of the model parameters we consider the evolution of the cosmological parameters (scale factor, energy density, Hubble function, deceleration parameter and luminosity distance, respectively), by using both analytical and numerical methods. In the large time limit the model describes an acceleratin...
Loop quantum cosmology of Bianchi type IX models
Wilson-Ewing, Edward
2010-01-01
The loop quantum cosmology "improved dynamics" of the Bianchi type IX model are studied. The action of the Hamiltonian constraint operator is obtained via techniques developed for the Bianchi type I and type II models, no new input is required. It is shown that the big bang and big crunch singularities are resolved by quantum gravity effects. We also present the effective equations which provide modifications to the classical equations of motion due to quantum geometry effects.
Loop quantum cosmology of Bianchi type IX models
Wilson-Ewing, Edward
2010-08-01
The loop quantum cosmology “improved dynamics” of the Bianchi type IX model are studied. The action of the Hamiltonian constraint operator is obtained via techniques developed for the Bianchi type I and type II models, no new input is required. It is shown that the big bang and big crunch singularities are resolved by quantum gravity effects. We also present effective equations which provide quantum geometry corrections to the classical equations of motion.
Cosmological bounds in MaVaN models
Energy Technology Data Exchange (ETDEWEB)
Boriero, D.F.; Holanda, P.C. de [Instituto de Fisica ' Gleb Wataghin' , Universidade Estadual de Campinas, UNICAMP, 13083-859, Campinas, Sao Paulo (Brazil)
2012-08-15
Mass varying neutrino (MaVaN) is a class of models which in cosmology try to explain the coincidence of dark energy density through a tracking mechanism related with neutrinos. This special model couples the quintessential scalar field with neutrino generating an effective mass which becomes variable. Furthermore, it has been shown that an additional coupling among the quintessential field and baryons could generate specific dependences of neutrino mass with baryonic density.
Cosmological model in 5D, stationarity, yes or no
Belayev, W B
1999-01-01
We consider cosmological model in 4+1 dimensions with variable scale factor in extra dimension and static external space. The time scale factor is changing. Variations of light velocity, gravity constant, mass and pressure are determined with four-dimensional projection of this space-time. Data obtained by space probes Viking on mission to Mars, Pioneer 10/11 and Ulysses are analyzed within the framework of this model.
A Dark Energy Model in Kaluza-Klein Cosmology
Mukhopadhyay, Utpal; Chakraborty, Ipsita; Ray, Saibal; Usmani, A. A.
2016-01-01
We study a dynamic Λ model with varying gravitational constant G under the Kaluza-Klein cosmology. Physical features and the limitations of the present model have been explored and discussed. Solutions are found mostly in accordance with the observed features of the accelerating universe. Interestingly, signature flipping of the deceleration parameter is noticed and the present age of the Universe is also attainable under certain stringent conditions. We find that the time variation of gravitational constant is not permitted without vintage Λ.
A Dark Energy Model in Kaluza-Klein Cosmology
Mukhopadhyay, Utpal; Ray, Saibal; Usmani, A A
2014-01-01
We study a dynamic $\\Lambda$ model with varying gravitational constant $G$ under the Kaluza-Klein cosmology. Physical features and the limitations of the present model have been explored and discussed. Solutions are found mostly in accordance with the observed features of the accelerating universe. Interestingly, signature flipping of the deceleration parameter is noticed and the present age of the Universe is also attainable under certain stringent conditions. We find that the time variation of gravitational constant is not permitted without vintage $\\Lambda$.
Bianchi type-V string cosmological models in general relativity
Indian Academy of Sciences (India)
Anil Kumar Yadav; Vineet Kumar Yadav; Lallan Yadav
2011-04-01
Bianchi type-V string cosmological models in general relativity are investigated. To get the exact solution of Einstein’s ﬁeld equations, we have taken some scale transformations used by Camci et al [Astrophys. Space Sci. 275, 391 (2001)]. It is shown that Einstein’s ﬁeld equations are solvable for any arbitrary cosmic scale function. Solutions for particular forms of cosmic scale functions are also obtained. Some physical and geometrical aspects of the models are discussed.
Robertson-Walker cosmological models with perfect fluid in general relativity
Institute of Scientific and Technical Information of China (English)
Rishi Kumar Tiwari
2011-01-01
Einstein's field equations with variable gravitational and cosmological constants are considered in the presence of perfect fluid for a Robertson-Walker universe by assuming the cosmological term to be proportional to R-m (R is a scale factor and m is a constant). A variety of solutions is presented. The physical significance of the cosmological models has also been discussed.
On multidimensional solutions in the Einstein-Gauss-Bonnet model with a cosmological term
Kobtsev, A A; Ernazarov, K K
2016-01-01
A D-dimensional gravitational model with Gauss-Bonnet and cosmological term is considered. When ansatz with diagonal cosmological metrics is adopted, we overview recent solutions for zero cosmological term and find new examples of solutions for non-zero cosmological term and D = 8 with exponential dependence of scale factors which describe an expansion of our 3-dimensional factor-space and contraction of 4-dimensional internal space.
The Cosmological Constant for the Crystalline Vacuum Cosmic Space Model
Montemayor-Aldrete, J A; Morales-Mori, A; Mendoza-Allende, A; Montemayor-Varela, A; Castillo-Mussot, M; Vazquez, G J
2005-01-01
The value of the cosmological constant arising from a crystalline model for vacuum cosmic space with lattice parameter of the order of the neutron radius [1] has been calculated. The model allows to solve, in an easy way, the problem of the cosmological constant giving the right order of magnitude, which corresponds very well with the mean value of matter density in the universe. The obtained value is about 10-48 Km-2. Diffraction experiments with non-thermal neutron beam in cosmic space are proposed to search for the possibility of crystalline structure of vacuum space and to measure the lattice parameter. PACS numbers: 98.80.Es, 04.20.-q, 03.65.-w, 61.50.-f, 98.80.Ft
First cosmological constraints on the Superfluid Chaplygin gas model
Lazkoz, Ruth; Salzano, Vincenzo
2012-01-01
In this work we set observational constraints of the Superfluid Chaplygin gas model, which gives a unified description of the dark sector of the Universe as a Bose-Einstein condensate (BEC) that behaves as dark energy (DE) while it is in the ground state and as dark matter (DM) when it is in the excited state. We first show and perform the various steps leading to a form of the equations suitable for the observational tests to be carried out. Then, by using a Markov Chain Monte Carlo (MCMC) code, we constrain the model with a sample of cosmology-independent long gamma-ray bursts (LGRBs) calibrated using their Type I Fundamental Plane, as well as the Union2.1 set and observational Hubble parameter data. In this analysis, using our cosmological constraints, we sketch the effective equation of state parameter and deceleration parameter, and we also obtain the redshift of the transition from deceleration to acceleration: $z_t$.
Constraints on cosmological models from lens redshift data
Cao, Shuo
2011-01-01
Strong lensing has developed into an important astrophysical tool for probing both cosmology and galaxies (their structures, formations, and evolutions). Now several hundreds of strong lens systems produced by massive galaxies have been discovered, which may form well-defined samples useful for statistical analyses. To collect a relatively complete lens redshift data from various large systematic surveys of gravitationally lensed quasars and check the possibility to use it as a future complementarity to other cosmological probes. We use the distribution of gravitationally-lensed image separations observed in the Cosmic Lens All-Sky Survey (CLASS), the PMN-NVSS Extragalactic Lens Survey (PANELS), the Sloan Digital Sky Survey (SDSS) and other surveys, considering a singular isothermal ellipsoid (SIE) model for galactic potentials as well as improved new measurements of the velocity dispersion function of galaxies based on the SDSS DR5 data and recent semi-analytical modeling of galaxy formation, to constrain tw...
The B-L phase transition. Implications for cosmology and neutrinos
Energy Technology Data Exchange (ETDEWEB)
Schmitz, Kai
2012-07-15
very heavy gravitinos, which are motivated by hints for the Higgs boson at the LHC. We find that the nonthermal production of pure wino or higgsino LSPs, i.e. weakly interacting massive particles (WIMPs), in heavy gravitino decays can account for the observed amount of dark matter, while simultaneously fulfilling the constraints imposed by primordial nucleosynthesis and leptogenesis, within a range of LSP, gravitino and neutrino masses. Besides its cosmological implications, the spontaneous breaking of B-L also naturally explains the small observed neutrino masses via the seesaw mechanism. Upon the seesaw model we impose a flavour structure of the Froggatt-Nielson type which, together with the known neutrino data, allows us to strongly contrain yet undetermined neutrino observables.
Perturbations of Kantowski-Sachs models with a cosmological constant
Keresztes, Zoltán; Bradley, Michael; Dunsby, Peter K S; Gergely, László Á
2013-01-01
We investigate perturbations of Kantowski-Sachs models with a positive cosmological constant, using the gauge invariant 1+3 and 1+1+2 covariant splits of spacetime together with a harmonic decomposition. The perturbations are assumed to be vorticity-free and of perfect fluid type, but otherwise include general scalar, vector and tensor modes. In this case the set of equations can be reduced to six evolution equations for six harmonic coefficients.
Wave functions in SUSY cosmological models with matter
Energy Technology Data Exchange (ETDEWEB)
Ortiz, C. [Instituto de Fisica de la Universidad de Guanajuato, A.P. E-143, C.P. 37150, Leon, Guanajuato (Mexico); Rosales, J.J. [Facultad de Ingenieria Mecanica Electrica y Electronica, Universidad de Guanajuato, Prolongacion Tampico 912, Bellavista, Salamanca, Guanajuato (Mexico); Socorro, J. [Instituto de Fisica de la Universidad de Guanajuato, A.P. E-143, C.P. 37150, Leon, Guanajuato (Mexico)]. E-mail: socorro@fisica.ugto.mx; Torres, J. [Instituto de Fisica de la Universidad de Guanajuato, A.P. E-143, C.P. 37150, Leon, Guanajuato (Mexico); Tkach, V.I. [Instituto de Fisica de la Universidad de Guanajuato, A.P. E-143, C.P. 37150, Leon, Guanajuato (Mexico)
2005-06-06
In this work we consider the n=2 supersymmetric superfield approach for the FRW cosmological model and the corresponding term of matter content, perfect fluid with barotropic state equation p={gamma}{rho}. We are able to obtain a normalizable wave function (at zero energy) of the universe. Besides, the mass parameter spectrum is found for the closed FRW case in the Schrodinger picture, being similar to those obtained by other methods, using a black hole system.
Stability of some Kaluza-Klein cosmological models
Energy Technology Data Exchange (ETDEWEB)
Barrow, J.D.; Stein-Schabes, J.
1986-02-06
The stability is examined of some exact Kaluza-Klein cosmological solutions that possess static extra dimensions and standard Friedman behaviour for the remaining three spatial dimensions. It is shown that even when the extra dimensions are asymptotically static they produce a deviation from Friedman behaviour in the observable three spatial dimensions. A similar effect is found for models with anisotropically expanding three-spaces. (orig.).
Cosmological Structure Formation in Decaying Dark Matter Models
Cheng, Dalong; Tang, Jiayu
2015-01-01
The standard cold dark matter (CDM) model predicts too many and too dense small structures. We consider an alternative model that the dark matter undergoes two-body decays with cosmological lifetime $\\tau$ into only one type of massive daughters with non-relativistic recoil velocity $V_k$. This decaying dark matter model (DDM) can suppress the structure formation below its free-streaming scale at time scale comparable to $\\tau$. Comparing with warm dark matter (WDM), DDM can better reduce the small structures while being consistent with high redshfit observations. We study the cosmological structure formation in DDM by performing self-consistent N-body simulations and point out that cosmological simulations are necessary to understand the DDM structures especially on non-linear scales. We propose empirical fitting functions for the DDM suppression of the mass function and the mass-concentration relation, which depend on the decay parameters lifetime $\\tau$ and recoil velocity $V_k$, and redshift. The fitting ...
Two Accurate Time-delay Distances from Strong Lensing: Implications for Cosmology
Suyu, S. H.; Auger, M. W.; Hilbert, S.; Marshall, P. J.; Tewes, M.; Treu, T.; Fassnacht, C. D.; Koopmans, L. V. E.; Sluse, D.; Blandford, R. D.; Courbin, F.; Meylan, G.
2013-01-01
Strong gravitational lenses with measured time delays between the multiple images and models of the lens mass distribution allow a one-step determination of the time-delay distance, and thus a measure of cosmological parameters. We present a blind analysis of the gravitational lens RXJ1131-1231 inco
Two Accurate Time-delay Distances from Strong Lensing : Implications for Cosmology
Suyu, S. H.; Auger, M. W.; Hilbert, S.; Marshall, P. J.; Tewes, M.; Treu, T.; Fassnacht, C. D.; Koopmans, L. V. E.; Sluse, D.; Blandford, R. D.; Courbin, F.; Meylan, G.
2013-01-01
Strong gravitational lenses with measured time delays between the multiple images and models of the lens mass distribution allow a one-step determination of the time-delay distance, and thus a measure of cosmological parameters. We present a blind analysis of the gravitational lens RXJ1131-1231 inco
Bianchi Type Ⅲ String Cosmological Model with Bulk Viscosity
Institute of Scientific and Technical Information of China (English)
WANGXing-Xiang
2004-01-01
The Bianchi type Ⅲ cosmological model for a cloud string with bulk viscosity are presented. To obtain a determinate model, an equation of state ρ=kλ and a relation between metric potentials B = Cn are assumed. The physical and geometric aspects of the model are also discussed. The model describes a shearing non-rotating continuously expanding universe with a big-bang start, and the relation between the coefficient of bulk viscosity and the energy density is ζ∝ρ1/2.
Bianchi Type Ⅲ String Cosmological Model with Bulk Viscosity
Institute of Scientific and Technical Information of China (English)
WANG Xing-Xiang
2004-01-01
The Bianchi type Ⅲ cosmological model for a cloud string with bulk viscosity are presented. To obtaina determinate model, an equation of state p = κλ and a relation between metric potentials B = Cn are assumed. Thephysical and geometric aspects of the model are also discussed. The model describes a shearing non-rotating continuouslyexpanding universe with a big-bang start, and the relation between the coefficient of bulk viscosity and the energy densityis ζ∝1 p1/2.
Stability analysis of cosmological models through Liapunov's method
Charters, T C; Mimoso, J P; Charters, Tiago C.; Mimoso, Jose P.
2001-01-01
We investigate the general asymptotic behaviour of Friedman-Robertson-Walker (FRW) models with an inflaton field, scalar-tensor FRW cosmological models and diagonal Bianchi-IX models by means of Liapunov's method. This method provides information not only about the asymptotic stability of a given equilibrium point but also about its basin of attraction. This cannot be obtained by the usual methods found in the literature, such as linear stability analysis or first order perturbation techniques. Moreover, Liapunov's method is also applicable to non-autonomous systems. We use this advantadge to investigate the mechanism of reheating for the inflaton field in FRW models.
On spherically symmetric singularity-free models in relativistic cosmology
Indian Academy of Sciences (India)
Ramesh Tikekar
2000-10-01
The introduction of time dependence through a scale factor in a non-conformally ﬂat static cosmological model whose spacetime can be embedded in a ﬁve demensional ﬂat spacetime is shown to give rise to two spherical models of universe ﬁlled with perfect ﬂuid acompannied with radial heat ﬂux without any Big Bang type singularity. The ﬁrst model describes an ever existing universe which witnesses a transition from state of contraction to that of ever expansion. The second model represents a universe oscillating between two regular states.
Renormalization group approach to causal bulk viscous cosmological models
Energy Technology Data Exchange (ETDEWEB)
Belinchon, J A [Grupo Inter-Universitario de Analisis Dimensional, Dept. Fisica ETS Arquitectura UPM, Av. Juan de Herrera 4, Madrid (Spain); Harko, T [Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong (China); Mak, M K [Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong (China)
2002-06-07
The renormalization group method is applied to the study of homogeneous and flat Friedmann-Robertson-Walker type universes, filled with a causal bulk viscous cosmological fluid. The starting point of the study is the consideration of the scaling properties of the gravitational field equations, the causal evolution equation of the bulk viscous pressure and the equations of state. The requirement of scale invariance imposes strong constraints on the temporal evolution of the bulk viscosity coefficient, temperature and relaxation time, thus leading to the possibility of obtaining the bulk viscosity coefficient-energy density dependence. For a cosmological model with bulk viscosity coefficient proportional to the Hubble parameter, we perform the analysis of the renormalization group flow around the scale-invariant fixed point, thereby obtaining the long-time behaviour of the scale factor.
The Cosmology of Generalized Modified Gravity Models
Carroll, S M; Duvvuri, V; Easson, D A; Trodden, M; Turner, M S; Carroll, Sean M.; Felice, Antonio De; Duvvuri, Vikram; Easson, Damien A.; Trodden, Mark; Turner, Michael S.
2005-01-01
We consider general curvature-invariant modifications of the Einstein-Hilbert action that become important only in regions of extremely low space-time curvature. We investigate the far future evolution of the universe in such models, examining the possibilities for cosmic acceleration and other ultimate destinies. The models generically possess de Sitter space as an unstable solution and exhibit an interesting set of attractor solutions which, in some cases, provide alternatives to dark energy models.
Cosmology of generalized modified gravity models
Carroll, Sean M.; de Felice, Antonio; Duvvuri, Vikram; Easson, Damien A.; Trodden, Mark; Turner, Michael S.
2005-03-01
We consider general curvature-invariant modifications of the Einstein-Hilbert action that become important only in regions of extremely low space-time curvature. We investigate the far future evolution of the Universe in such models, examining the possibilities for cosmic acceleration and other ultimate destinies. The models generically possess de Sitter space as an unstable solution and exhibit an interesting set of attractor solutions which, in some cases, provide alternatives to dark energy models.
Ignat'ev, Yu G
2016-01-01
In this paper we investigate the asymptotic behavior of the cosmological model based on phantom scalar field on the ground of qualitative analysis of the system of the cosmological model's differential equations and show that as opposed to models with classical scalar field, such models have stable asymptotic solutions with constant value of the potential both in infinite past and infinite future. We also develop numerical models of the cosmological evolution models with phantom scalar field in this paper. {\\bf keywords}: cosmological model, phantom scalar field, quality analysis, asymptotic behavior, numerical simulation, numerical gravitation.\\\\ {\\bf PACS}: 04.20.Cv, 98.80.Cq, 96.50.S 52.27.Ny
Implication of Sterile Fermions in Particle Physics and Cosmology
Lucente, Michele
2016-01-01
The neutrino mass generation mechanism, the nature of dark matter and the origin of the baryon asymmetry of the Universe are three compelling questions that cannot be accounted for in the Standard Model of particle physics. In this thesis we focus on all these issues by providing a possible solution in terms of a minimal extension of the Standard Model, consisting in the addition of a set of sterile fermions to the field content of the theory. Sterile fermions are gauge singlet fields, that can interact via mixing with the active neutrinos. We focus on the Inverse Seesaw mechanism, which is characterised by a low (TeV or lower) new physics scale and that can be tested in current and future experimental facilities. We present the model building analysis that points towards the minimal realisations of the mechanism, and the phenomenological study in order to accommodate light neutrino masses and to impose all the relevant experimental constraints in the model, as well as the expected experimental signatures. We...
Cosmological Perturbations in Phantom Dark Energy Models
Directory of Open Access Journals (Sweden)
Imanol Albarran
2017-03-01
Full Text Available The ΛCDM paradigm, characterised by a constant equation of state w = − 1 for dark energy, is the model that better fits observations. However, the same observations strongly support the possibility of a dark energy content where the corresponding equation of state is close to but slightly smaller than − 1 . In this regard, we focus on three different models where the dark energy content is described by a perfect fluid with an equation of state w ≲ − 1 which can evolve or not. The three proposals show very similar behaviour at present, while the asymptotic evolution of each model drives the Universe to different abrupt events known as (i Big Rip; (ii Little Rip (LR; and (iii Little Sibling of the Big Rip. With the aim of comparing these models and finding possible imprints in their predicted matter distribution, we compute the matter power spectrum and the growth rate f σ 8 . We conclude that the model which induces a LR seems to be favoured by observations.
The rotation curve of spiral galaxies and its cosmological implications
Florido, E
2000-01-01
We review the topic of rotation curves of spiral galaxies emphasizing the standard interpretation as evidence for the existence of dark matter halos. Galaxies other than spirals and late-type dwarfs may also possess great amounts of dark matter, and therefore ellipticals, dwarf spirals, lenticulars and polar ring galaxies are also considered. Furthermore, other methods for determining galactic dark matter, such as those provided by binaries, satellites or globular clusters, have to be included. Cold dark matter hierarchical models constitute the standard way to explain rotation curves, and thus the problem becomes just one aspect of a more general theory explaining structure and galaxy formation. Alternative theories also are included. In the magnetic model, rotation curves could also be a particular aspect of the whole history of cosmic magnetism during different epochs of the Universe. Modifications of Newtonian Dynamics provide another interesting possibility which is discussed here.
Redshift remapping and cosmic acceleration in dark-matter-dominated cosmological models
Wojtak, Radosław
2016-01-01
The standard relation between the cosmological redshift and cosmic scale factor underlies cosmological inference from virtually all kinds of cosmological observations, leading to the emergence of the LambdaCDM cosmological model. This relation is not a fundamental theory and thus observational determination of this function (redshift remapping) should be regarded as an insightful alternative to holding its standard form in analyses of cosmological data. Here we present non-parametric reconstructions of redshift remapping in dark-matter-dominated models and constraints on cosmological parameters from a joint analysis of all primary cosmological probes including the local measurement of the Hubble constant, Type Ia supernovae, baryonic acoustic oscillations (BAO), Planck observations of the cosmic microwave background (CMB) radiation (temperature power spectrum) and cosmic chronometers. The reconstructed redshift remapping points to an additional boost of redshift operating in late epoch of cosmic evolution, bu...
Ignat'ev, Yurii
2016-01-01
On the basis of qualitative analysis of the system of differential equations of the standard cosmological model it is shown that in the case of zero cosmological constant this system has a stable center corresponding to zero values of potential and its derivative at infinity. Thus, the cosmological model based on single massive classical scalar field in infinite future would give a flat Universe. The carried out numerical simulation of the dynamic system corresponding to the system of Einstein - Klein - Gordon equations showed that at great times of the evolution the invariant cosmological acceleration has an oscillating character and changes from $-2$ (braking), to $+1$ (acceleration). Average value of the cosmological acceleration is negative and is equal to $-1/2$. Oscillations of the cosmological acceleration happen on the background of rapidly falling Hubble constant. In the case of nonzero value of the cosmological constant depending on its value there are possible three various qualitative behavior typ...
Krauss, Lawrence M; Dent, James
2008-05-01
We describe here how the late time behavior of the quantum mechanical decay of unstable states, which is predicted to deviate from an exponential form, may have important cosmological implications. It may increase the likelihood of eternal inflation and may enhance the likelihood of observing a small vacuum energy at late times versus possible late time decay into a large negative energy (anti-de Sitter space) vacuum state. Open questions include the following: How can internal observations made impact upon the wave function of the Universe and hence upon its decay characteristics?
On hyperbolicity violations in cosmological models with vector fields
Golovnev, Alexey
2014-01-01
Cosmological models with vector fields received much attention in recent years. Unfortunately, most of them are plagued with severe instabilities or other problems. In particular, it was noted by G. Esposito-Farese, C. Pitrou and J.-Ph. Uzan in arXiv:0912.0481 that the models with a non-linear function of the Maxwellian kinetic term do always imply violations of hyperbolicity somewhere in the phase space. In this work we make this statement more precise in several respects and show that those violations may not be present around spatially homogeneous configurations of the vector field.
Constraining interacting dark energy models with latest cosmological observations
Xia, Dong-Mei; Wang, Sai
2016-11-01
The local measurement of H0 is in tension with the prediction of Λ cold dark matter 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 cosmic microwave background, the baryon acoustic oscillation, large-scale structure, supernovae, H(z) and H0 to constrain several interacting dark energy models. Our results show no significant indications for the interaction between dark energy and dark matter. The H0 tension can be moderately alleviated, but not totally released.
Constraining interacting dark energy models with latest cosmological observations
Xia, Dong-Mei
2016-01-01
The local measurement of $H_0$ is in tension with the prediction of $\\Lambda$CDM model based on the Planck data. This tension may imply that dark energy is strengthened in the late-time Universe. We employ the latest cosmological observations on CMB, BAO, LSS, SNe, $H(z)$ and $H_0$ to constrain several interacting dark energy models. Our results show no significant indications for the interaction between dark energy and dark matter. The $H_0$ tension can be moderately alleviated, but not totally released.
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...
Salazar-Albornoz, Salvador; Sánchez, Ariel G.; Grieb, Jan Niklas; Crocce, Martin; Scoccimarro, Roman; Alam, Shadab; Beutler, Florian; Brownstein, Joel R.; Chuang, Chia-Hsun; Kitaura, Francisco-Shu; Olmstead, Matthew D.; Percival, Will J.; Prada, Francisco; Rodríguez-Torres, Sergio; Samushia, Lado; Tinker, Jeremy; Thomas, Daniel; Tojeiro, Rita; Wang, Yuting; Zhao, Gong-bo
2017-07-01
We investigate the cosmological implications of studying galaxy clustering using a tomographic approach applied to the final Baryon Oscillation Spectroscopic Survey (BOSS) DR12 galaxy sample, including both auto- and cross-correlation functions between redshift shells. We model the signal of the full shape of the angular correlation function, ω(θ), in redshift bins using state-of-the-art modelling of non-linearities, bias and redshift-space distortions. We present results on the redshift evolution of the linear bias of BOSS galaxies, which cannot be obtained with traditional methods for galaxy-clustering analysis. We also obtain constraints on cosmological parameters, combining this tomographic analysis with measurements of the cosmic microwave background (CMB) and Type Ia supernova (SNIa). We explore a number of cosmological models, including the standard Λ cold dark matter model and its most interesting extensions, such as deviations from wDE = -1, non-minimal neutrino masses, spatial curvature and deviations from general relativity (GR) using the growth-index γ parametrization. These results are, in general, comparable to the most precise present-day constraints on cosmological parameters, and show very good agreement with the standard model. In particular, combining CMB, ω(θ) and SNIa, we find a value of wDE consistent with -1 to a precision better than 5 per cent when it is assumed to be constant in time, and better than 6 per cent when we also allow for a spatially curved Universe.
Superpartner mass spectrum and cosmological implications from orbifolds
Energy Technology Data Exchange (ETDEWEB)
Schmidt-Hoberg, K.
2007-06-15
This thesis is devoted to orbifolded quantum field theories in six spacetime dimensions. Within the framework of T{sup 2}/Z{sub 2} and T{sup 2}/(Z{sub 2} x Z{sub 2}{sup PS} x Z{sub 2}{sup GG}) we calculate the Casimir energy, which yields an essential contribution to the modulus potential. Turning to more phenomenological aspects, we study gaugino-mediated supersymmetry breaking in a six-dimensional SO(10) orbifold GUT model where quarks and leptons are mixtures of brane and bulk fields. We derived bounds on the soft supersymmetry breaking parameters and calculate the superparticle mass spectrum. Higgs fields are bulk fields, and in general their masses differ from those of squarks and sleptons at the unification scale. As a consequence, at different points in parameter space, the gravitino, a neutralino or a scalar lepton can be the lightest or next-to-lightest superparticle. We investigate the constraints from primordial nucleosynthesis on the different scenarios. While neutralino dark matter and gravitino dark matter with a {nu} next-to-lightest superparticle are consistent for a wide range of parameters, gravitino dark matter with a {tau} next-to-lightest superparticle is strongly constrained.
Scale invariant cosmology III: dynamical models and comparisons with observations
Maeder, Andre
2016-01-01
We examine the properties of the scale invariant cosmological models, also making the specific hypothesis of the scale invariance of the empty space at large scales. Numerical integrations of the cosmological equations for different values of the curvature parameter k and of the density parameter Omega_m are performed. We compare the dynamical properties of the models to the observations at different epochs. The main numerical data and graphical representations are given for models computed with different curvatures and density parameters. The models with non-zero density start explosively with first a braking phase followed by a continuously accelerating expansion. The comparison of the models with the recent observations from supernovae SN Ia, BAO and CMB data from Planck 2015 shows that the scale invariant model with k=0 and Omega_m=0.30 very well fits the observations in the usual Omega_m vs. Omega_Lambda plane and consistently accounts for the accelerating expansion or dark energy. The expansion history ...
Artymowski, Michał; Wells, James D
2016-01-01
We consider various models realizing baryogenesis during the electroweak phase transition (EWBG). Our focus is their possible detection in future collider experiments and possible observation of gravitational waves emitted during the phase transition. We also discuss the possibility of a non-standard cosmological history which can facilitate EWBG. We show how acceptable parameter space can be extended due to such a modification and conclude that next generation precision experiments such as the ILC will be able to confirm or falsify many models realizing EWBG. We also show that, in general, collider searches are a more powerful probe than gravitational wave searches. However, observation of a deviation from the SM without any hints of gravitational waves can point to models with modified cosmological history that generically enable EWBG with weaker phase transition and thus, smaller GW signals.
A comparison of cosmological models using time delay lenses
Energy Technology Data Exchange (ETDEWEB)
Wei, Jun-Jie; Wu, Xue-Feng; Melia, Fulvio, E-mail: jjwei@pmo.ac.cn, E-mail: xfwu@pmo.ac.cn, E-mail: fmelia@email.arizona.edu [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)
2014-06-20
The use of time-delay gravitational lenses to examine the cosmological expansion introduces a new standard ruler with which to test theoretical models. The sample suitable for this kind of work now includes 12 lens systems, which have thus far been used solely for optimizing the parameters of ΛCDM. In this paper, we broaden the base of support for this new, important cosmic probe by using these observations to carry out a one-on-one comparison between competing models. The currently available sample indicates a likelihood of ∼70%-80% that the R {sub h} = ct universe is the correct cosmology versus ∼20%-30% for the standard model. This possibly interesting result reinforces the need to greatly expand the sample of time-delay lenses, e.g., with the successful implementation of the Dark Energy Survey, the VST ATLAS survey, and the Large Synoptic Survey Telescope. In anticipation of a greatly expanded catalog of time-delay lenses identified with these surveys, we have produced synthetic samples to estimate how large they 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 ∼150 time-delay lenses would be sufficient to rule out R {sub h} = ct at this level of accuracy, while ∼1000 time-delay lenses would be required to rule out ΛCDM if the real universe is instead R {sub h} = ct. This difference in required sample size reflects the greater number of free parameters available to fit the data with ΛCDM.
Cosmological study of reconstructed f(T) models
Jawad, Abdul; Rani, Shamaila; Saleem, M.
2017-04-01
In this paper, we construct f(T) models by using some dark energy models taking FRW space-time under reconstruction scenario. These dark energy models consist of pilgrim dark energy model with event horizon and Granda-Oliveros as infrared cutoff and higher order time derivatives of Hubble parameter. Using these models we drive the cosmological parameters such as equation of state, square speed of sound and ωT-ωT' plane taking power-law form of scale factor. We discuss these parameters graphically for different values of scale factor parameter. The first and second models represent quintessence and phantom era with stable behavior and freezing region for smaller values of scale factor parameter. The third model shows unstable behavior while phantom era of the universe.
Examining subgrid models of supermassive black holes in cosmological simulation
Sutter, P M
2010-01-01
While supermassive black holes (SMBHs) play an important role in galaxy and cluster evolution, at present they can only be included in large-scale cosmological simulation via subgrid techniques. However, these subgrid models have not been studied in a systematic fashion. Using a newly-developed fast, parallel spherical overdensity halo finder built into the simulation code FLASH, we perform a suite of dark matter-only cosmological simulations to study the effects of subgrid model choice on relations between SMBH mass and dark matter halo mass and velocity dispersion. We examine three aspects of SMBH subgrid models: the choice of initial black hole seed mass, the test for merging two black holes, and the frequency of applying the subgrid model. We also examine the role that merging can play in determining the relations, ignoring the complicating effects of SMBH-driven accretion and feedback. We find that the choice of subgrid model can dramatically affect the black hole merger rate, the cosmic SMBH mass densit...
Pradhan, Anirudh; Rikhvitsky, Victor
2013-01-01
The present study deals with the exact solutions of the Einstein's field equations with variable gravitational and cosmological "constants" for a spatially homogeneous and anisotropic Bianchi type-I space-time. To study the transit behaviour of Universe, we consider a law of variation of scale factor $a(t) = \\left(t^{k} e^{t}\\right)^{\\frac{1}{n}}$ which yields a time dependent deceleration parameter (DP) $q = - 1 + \\frac{nk}{(k + t)^{2}}$, comprising a class of models that depicts a transition of the universe from the early decelerated phase to the recent accelerating phase. We find that the time dependent DP is reasonable for the present day Universe and give an appropriate description of the evolution of the universe. For $n = 0.27k$, we obtain $q_{0} = -0.73$ which is similar to observed value of DP at present epoch. It is also observed that for $n \\geq 2$ and $k = 1$, we obtain a class of transit models of the universe from early decelerating to present accelerating phase. For $k = 0$, the universe has no...
Anisotropic models are unitary: A rejuvenation of standard quantum cosmology
Pal, Sridip
2016-01-01
The present work proves that the folk-lore of the pathology of non-conservation of probability in quantum anisotropic models is wrong. It is shown in full generality that all operator ordering can lead to a Hamiltonian with a self-adjoint extension as long as it is constructed to be a symmetric operator, thereby making the problem of non-unitarity in context of anisotropic homogeneous model a ghost. Moreover, it is indicated that the self-adjoint extension is not unique and this non-uniqueness is suspected not to be a feature of Anisotropic model only, in the sense that there exists operator orderings such that Hamiltonian for an isotropic homogeneous cosmological model does not have unique self-adjoint extension, albeit for isotropic model, there is a special unique extension associated with quadratic form of Hamiltonian i.e {\\it Friedrichs extension}. Details of calculations are carried out for a Bianchi III model.
Cosmological data analysis of f(R) gravity models
Girones, Z; Mena, O; Pena-Garay, C; Rius, N
2009-01-01
A class of well-behaved modified gravity models with long enough matter domination epoch and a late-time accelerated expansion is confronted with SNIa, CMB, SDSS, BAO and H(z) galaxy ages data, as well as current measurements of the linear growth of structure. We show that the combination of geometrical probes and growth data exploited here allows to rule out f(R) gravity models, in particular, the logarithmic of curvature model. We also apply solar system tests to the models in agreement with the cosmological data. We find that the exponential of the inverse of the curvature model satisfies all the observational tests considered and we derive the allowed range of parameters. Current data still allows for small deviations of Einstein gravity. Future, high precision growth data, in combination with expansion history data, will be able to distinguish tiny modifications of standard gravity from the LambdaCDM model.
Cosmological data analysis of f(R) gravity models
Energy Technology Data Exchange (ETDEWEB)
Gironés, Z.; Marchetti, A.; Mena, O.; Peña-Garay, C.; Rius, N., E-mail: girones@ific.uv.es, E-mail: alida.marchetti@unimi.it, E-mail: omena@ific.uv.es, E-mail: carlos.penya@ific.uv.es, E-mail: nuria@ific.uv.es [Depto. de Física Teórica, IFIC, Universidad de Valencia-CSIC, Edificio de Institutos de Paterna, Apt. 22085, 46071 Valencia (Spain)
2010-11-01
A class of well-behaved modified gravity models with long enough matter domination epoch and a late-time accelerated expansion is confronted with SNIa, CMB, SDSS, BAO and H(z) galaxy ages data, as well as current measurements of the linear growth of structure. We show that the combination of geometrical probes and growth data exploited here allows to rule out f(R) gravity models, in particular, the logarithmic of curvature model. We also apply solar system tests to the models in agreement with the cosmological data. We find that the exponential of the inverse of the curvature model satisfies all the observational tests considered and we derive the allowed range of parameters. Current data still allows for small deviations of Einstein gravity. Future, high precision growth data, in combination with expansion history data, will be able to distinguish tiny modifications of standard gravity from the ΛCDM model.
Cosmological model with interactions in the dark sector
Chimento, Luis P; Kremer, Gilberto M
2007-01-01
A cosmological model is proposed for the current Universe consisted of non-interacting baryonic matter and interacting dark components. The dark energy and dark matter are coupled through their effective barotropic indexes, which are considered as functions of the ratio between their energy densities. It is investigated two cases where the ratio is asymptotically stable and their parameters are adjusted by considering best fits to Hubble function data. It is shown that the deceleration parameter, the densities parameters, and the luminosity distance have the correct behavior which is expected for a viable present scenario of the Universe.
Testing coupled dark energy models with their cosmological background evolution
van de Bruck, Carsten; Morrice, Jack
2016-01-01
We consider a cosmology in which dark matter and a quintessence scalar field responsible for the acceleration of the Universe are allowed to interact. Allowing for both conformal and disformal couplings, we perform a global analysis of the constraints on our model using Hubble parameter measurements, baryon acoustic oscillation distance measurements, and a Supernovae Type Ia data set. We find that the additional disformal coupling relaxes the conformal coupling constraints. Moreover we show that, at the background level, a disformal interaction within the dark sector is preferred to both $\\Lambda$CDM and uncoupled quintessence, hence favouring interacting dark energy.
The adhesion model as a field theory for cosmological clustering
Energy Technology Data Exchange (ETDEWEB)
Rigopoulos, Gerasimos, E-mail: rigopoulos@thphys.uni-heidelberg.de [Institut für Theoretische Physik, Universität Heidelberg, Philosophenweg 12, Heidelberg, 69120 Germany (Germany)
2015-01-01
The adhesion model has been proposed in the past as an improvement of the Zel'dovich approximation, providing a good description of the formation of the cosmic web. We recast the model as a field theory for cosmological large scale structure, adding a stochastic force to account for power generated from very short, highly non-linear scales that is uncorrelated with the initial power spectrum. The dynamics of this Stochastic Adhesion Model (SAM) is reminiscent of the well known Kardar-Parisi-Zhang equation with the difference that the viscosity and the noise spectrum are time dependent. Choosing the viscosity proportional to the growth factor D restricts the form of noise spectrum through a 1-loop renormalization argument. For this choice, the SAM field theory is renormalizable to one loop. We comment on the suitability of this model for describing the non-linear regime of the CDM power spectrum and its utility as a relatively simple approach to cosmological clustering.
Tachyonization of the $\\La$CDM cosmological model
Chimento, Luis P; Kremer, Gilberto M; Ribas, Marlos O
2008-01-01
In this work a tachyonization of the $\\Lambda$CDM model for a spatially flat Friedmann-Robertson-Walker space-time is proposed. A tachyon field and a cosmological constant are considered as the sources of the gravitational field. Starting from a stability analysis and from the exact solutions for a standard tachyon field driven by a given potential, the search for a large set of cosmological models which contain the $\\Lambda$CDM model is investigated. By the use of internal transformations two new kinds of tachyon fields are derived from the standard tachyon field, namely, a complementary and a phantom tachyon fields. Numerical solutions for the three kinds of tachyon fields are determined and it is shown that the standard and complementary tachyon fields reproduces the $\\Lambda$CDM model as a limiting case. The standard tachyon field can also describe a transition from an accelerated to a decelerated regime, behaving as an inflaton field at early times and as a matter field at late times. The complementary t...
Nonspherical Szekeres models in the language of cosmological perturbations
Sussman, Roberto A.; Hidalgo, Juan Carlos; Delgado Gaspar, Ismael; Germán, Gabriel
2017-03-01
We study the differences and equivalences between the nonperturbative description of the evolution of cosmic structure furnished by the Szekeres dust models (a nonspherical exact solution of Einstein's equations) and the dynamics of cosmological perturbation theory (C P T ) for dust sources in a Λ CDM background. We show how the dynamics of Szekeres models can be described by evolution equations given in terms of "exact fluctuations" that identically reduce (at all orders) to evolution equations of C P T in the comoving isochronous gauge. We explicitly show how Szekeres linearized exact fluctuations are specific (deterministic) realizations of standard linear perturbations of C P T given as random fields, but, as opposed to the latter perturbations, they can be evolved exactly into the full nonlinear regime. We prove two important results: (i) the conservation of the curvature perturbation (at all scales) also holds for the appropriate linear approximation of the exact Szekeres fluctuations in a Λ CDM background, and (ii) the different collapse morphologies of Szekeres models yields, at nonlinear order, different functional forms for the growth factor that follows from the study of redshift space distortions. The metric-based potentials used in linear C P T are computed in terms of the parameters of the linearized Szekeres models, thus allowing us to relate our results to linear C P T results in other gauges. We believe that these results provide a solid starting stage to examine the role of non-perturbative general relativity in current cosmological research.
Forte, Mónica
2016-01-01
We show the kinematic equivalence between cosmological models driven by Dirac-Born-Infeld fields $\\phi$ with constant proper velocity of the brane and exponential potential $V=V_0e^{-B\\phi}$ and interactive cosmological systems with Modified Holographic Ricci type fluids as dark energy in flat Friedmann-Robertson-Walker cosmologies.
Constraints On Holographic Cosmological Models From Gamma Ray Bursts
Rivera, Alexander Bonilla
2016-01-01
We use Gamma Ray Bursts (GRBs) data to put additional constraints on a set of holographic dark energy models. GRBs are the most energetic events in the Universe and provide a complementary probe of dark energy by allowing the measurement of cosmic expansion history that extends to redshifts greater than 6 and they are complementary to SNIa test. We found that the LCDM model is the best fit to the data, although a preliminary statistical analysis seems to indicate that the holographic models studied show interesting agreement with observations, except Ricci Scale CPL model. These results show the importance of GRBs measurements to provide additional observational constraints to alternative cosmological models, which are necessary to clarify the way in the paradigm of dark energy or potential alternatives.
A Comparison of Cosmological Models Using Strong Gravitational Lensing Galaxies
Melia, Fulvio; Wu, Xue-Feng
2014-01-01
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, and carry out a one-on-one comparison between the standard model, LCDM, and the R_h=ct Universe. 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. 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 o...
Investigation of dark matter-dark energy interaction cosmological model
Wang, J S
2014-01-01
In this paper, we test the dark matter-dark energy interacting cosmological model with a dynamic equation of state $w_{DE}(z)=w_{0}+w_{1}z/(1+z)$, using type Ia supernovae (SNe Ia), Hubble parameter data, baryonic acoustic oscillation (BAO) measurements, and the cosmic microwave background (CMB) observation. This interacting cosmological model has not been studied before. The best-fitted parameters with $1 \\sigma$ uncertainties are $\\delta=-0.022 \\pm 0.006$, $\\Omega_{DM}^{0}=0.213 \\pm 0.008$, $w_0 =-1.210 \\pm 0.033$ and $w_1=0.872 \\pm 0.072$ with $\\chi^2_{min}/dof = 0.990$. At the $1 \\sigma$ confidence level, we find $\\delta<0$, which means that the energy transfer prefers from dark matter to dark energy. We also find that the SNe Ia are in tension with the combination of CMB, BAO and Hubble parameter data. The evolution of $\\rho_{DM}/\\rho_{DE}$ indicates that this interacting model is a good approach to solve the coincidence problem, because the $\\rho_{DE}$ decrease with scale factor $a$. The transition r...
A Comparison of Cosmological Models Using Time Delay Lenses
Wei, Jun-Jie; Melia, Fulvio
2014-01-01
The use of time-delay gravitational lenses to examine the cosmological expansion introduces a new standard ruler with which to test theoretical models. The sample suitable for this kind of work now includes 12 lens systems, which have thus far been used solely for optimizing the parameters of $\\Lambda$CDM. In this paper, we broaden the base of support for this new, important cosmic probe by using these observations to carry out a one-on-one comparison between {\\it competing} models. The currently available sample indicates a likelihood of $\\sim 70-80%$ that the $R_{\\rm h}=ct$ Universe is the correct cosmology versus $\\sim 20-30%$ for the standard model. This possibly interesting result reinforces the need to greatly expand the sample of time-delay lenses, e.g., with the successful implementation of the Dark Energy Survey, the VST ATLAS survey, and the Large Synoptic Survey Telescope. In anticipation of a greatly expanded catalog of time-delay lenses identified with these surveys, we have produced synthetic sa...
Bothun, Greg
2011-10-01
Ever since Aristotle placed us, with certainty, in the Center of the Cosmos, Cosmological models have more or less operated from a position of known truths for some time. As early as 1963, for instance, it was ``known'' that the Universe had to be 15-17 billion years old due to the suspected ages of globular clusters. For many years, attempts to determine the expansion age of the Universe (the inverse of the Hubble constant) were done against this preconceived and biased notion. Not surprisingly when more precise observations indicated a Hubble expansion age of 11-13 billion years, stellar models suddenly changed to produce a new age for globular cluster stars, consistent with 11-13 billion years. Then in 1980, to solve a variety of standard big bang problems, inflation was introduced in a fairly ad hoc manner. Inflation makes the simple prediction that the net curvature of spacetime is zero (i.e. spacetime is flat). The consequence of introducing inflation is now the necessary existence of a dark matter dominated Universe since the known baryonic material could comprise no more than 1% of the necessary energy density to make spacetime flat. As a result of this new cosmological ``truth'' a significant world wide effort was launched to detect the dark matter (which obviously also has particle physics implications). To date, no such cosmological component has been detected. Moreover, all available dynamical inferences of the mass density of the Universe showed in to be about 20% of that required for closure. This again was inconsistent with the truth that the real density of the Universe was the closure density (e.g. Omega = 1), that the observations were biased, and that 99% of the mass density had to be in the form of dark matter. That is, we know the universe is two component -- baryons and dark matter. Another prevailing cosmological truth during this time was that all the baryonic matter was known to be in galaxies that populated our galaxy catalogs. Subsequent
The Janus Cosmological Model (JCM) : An answer to the missing cosmological antimatter
D'Agostini, Gilles; Petit, Jean-Pierre
2017-01-01
Cosmological antimatter absence remains unexplained. Twin universes 1967 Sakarov's model suggests an answer: excess of matter and anti-quarks production in our universe is balanced by equivalent excess of antimatter and quark in twin universe. JCM provides geometrical framework, with a single manifold , two metrics solutions of two coupled field equations, to describe two populations of particles, one with positive energy-mass and the other with negative energy-mass : the `twin matter'. In a quantum point of view, it's a copy of the standard matter but with negative mass and energy. The matter-antimatter duality holds in both sectors. The standard and twin matters do not interact except through the gravitational coupling expressed in field equations. The twin matter is unobservable from matter-made apparatus. Field equations shows that matter and twin matter repel each other. Twin matter surrounding galaxies explains their confinement (dark matter role) and, in the dust universe era, mainly drives the process of expansion of the positive sector, responsible of the observed acceleration (dark energy role).
Two Accurate Time-delay Distances from Strong Lensing: Implications for Cosmology
Suyu, S. H.; Auger, M. W.; Hilbert, S.; Marshall, P. J.; Tewes, M.; Treu, T.; Fassnacht, C. D.; Koopmans, L. V. E.; Sluse, D.; Blandford, R. D.; Courbin, F.; Meylan, G.
2013-04-01
Strong gravitational lenses with measured time delays between the multiple images and models of the lens mass distribution allow a one-step determination of the time-delay distance, and thus a measure of cosmological parameters. We present a blind analysis of the gravitational lens RXJ1131-1231 incorporating (1) the newly measured time delays from COSMOGRAIL, the COSmological MOnitoring of GRAvItational Lenses, (2) archival Hubble Space Telescope imaging of the lens system, (3) a new velocity-dispersion measurement of the lens galaxy of 323 ± 20 km s-1 based on Keck spectroscopy, and (4) a characterization of the line-of-sight structures via observations of the lens' environment and ray tracing through the Millennium Simulation. Our blind analysis is designed to prevent experimenter bias. The joint analysis of the data sets allows a time-delay distance measurement to 6% precision that takes into account all known systematic uncertainties. In combination with the Wilkinson Microwave Anisotropy Probe seven-year (WMAP7) data set in flat wCDM cosmology, our unblinded cosmological constraints for RXJ1131-1231 are H_0=80.0^{+5.8}_{-5.7} km s^{-1} Mpc^{-1}, Ωde = 0.79 ± 0.03, and w=-1.25^{+0.17}_{-0.21}. We find the results to be statistically consistent with those from the analysis of the gravitational lens B1608+656, permitting us to combine the inferences from these two lenses. The joint constraints from the two lenses and WMAP7 are H_0=75.2^{+4.4}_{-4.2} km s^{-1} Mpc^{-1}, Ω _de=0.76^{+0.02}_{-0.03}, and w = -1.14^{+0.17}_{-0.20} in flat wCDM, and H_0=73.1^{+2.4}_{-3.6} km s^{-1} Mpc^{-1}, Ω_{Λ}= 0.75^{+0.01}_{-0.02}, and Ω_k=0.003^{+0.005}_{-0.006} in open ΛCDM. Time-delay lenses constrain especially tightly the Hubble constant H 0 (5.7% and 4.0% respectively in wCDM and open ΛCDM) and curvature of the universe. The overall information content is similar to that of Baryon Acoustic Oscillation experiments. Thus, they complement well other cosmological probes
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.)
Cosmological degeneracy versus cosmography: a cosmographic dark energy model
Luongo, Orlando; Troisi, Antonio
2015-01-01
In this work we use cosmography to alleviate the degeneracy among cosmological models, proposing a way to parameterize matter and dark energy in terms of cosmokinematics quantities. The recipe of using cosmography allows to expand observable quantities in Taylor series and to directly compare those expansions with data. We adopt this strategy and we propose a fully self-consistent parametrization of the total energy density driving the late time universe speed up. Afterwards, we describe a feasible \\emph{cosmographic dark energy model}, in which matter is fixed whereas dark energy evolves by means of the cosmographic series. Our technique provides robust constraints on cosmokinematic parameters, permitting one to separately bound matter from dark energy densities. Our cosmographic dark energy model turns out to be one parameter only, but differently from the $\\Lambda$CDM paradigm, it does not contain ansatz on the dark energy form. In addition, we even determine the free parameter of our model in suitable $1\\...
Some Exact Solutions of Magnetized viscous model in String Cosmology
Singh, C P
2012-01-01
In this paper we study anisotropic Bianchi-V universe with magnetic field and bulk viscous fluid in string cosmology. Exact solutions of the field equations are obtained by using the equation of state for a cloud of strings and a relationship between bulk viscous coefficient and expansion scalar. The bulk viscous coefficient is assumed to be inversely proportional to the expansion scalar. It is interesting to examine the effects of magnetized bulk viscous string model in early and late stages of the evolution of the universe. This paper investigates the different string models like geometrical(Nambu string), Takabayashi (p-string) and Reddy string models by taking certain physical conditions. The introduction of magnetic field or bulk viscosity or both results in rapid change in scale factors as well as in the classical potential. The presence of viscosity prevents the universe to be empty in its future evolution. The physical and geometrical aspects of each string model are discussed in detail.
Sequestered String Models: Supersymmetry Breaking and Cosmological Applications
Muia, Francesco
2016-01-01
In the present thesis I studied the phenomenology arising from a class of string models called sequestered compactifications, which were born with the aim of getting low-energy SUSY from strings. This is not an easy task if combined with cosmological constraints, since the mechanism of moduli stabilization fixes both the scale of supersymmetric particles and the scale of moduli, which tend to be of the same order. However, if on the one hand supersymmetric particles with TeV mass are desired in order to address the hierarchy problem, on the other hand the cosmological moduli problem requires the moduli to be heavier than 100 TeV. The specific setup of sequestered compactifications makes this hierarchy achievable, at least in principle: as in these models the visible sector is located on a stack of D3-branes at singularities, a physical separation between the visible degrees of freedom and the SUSY-breaking sources takes place. Such decoupling translates into a hierarchy between the scale of SUSY-breaking and ...
Mathematical Structure of Loop Quantum Cosmology: Homogeneous Models
Directory of Open Access Journals (Sweden)
Martin Bojowald
2013-12-01
Full Text Available The mathematical structure of homogeneous loop quantum cosmology is analyzed, starting with and taking into account the general classification of homogeneous connections not restricted to be Abelian. As a first consequence, it is seen that the usual approach of quantizing Abelian models using spaces of functions on the Bohr compactification of the real line does not capture all properties of homogeneous connections. A new, more general quantization is introduced which applies to non-Abelian models and, in the Abelian case, can be mapped by an isometric, but not unitary, algebra morphism onto common representations making use of the Bohr compactification. Physically, the Bohr compactification of spaces of Abelian connections leads to a degeneracy of edge lengths and representations of holonomies. Lifting this degeneracy, the new quantization gives rise to several dynamical properties, including lattice refinement seen as a direct consequence of state-dependent regularizations of the Hamiltonian constraint of loop quantum gravity. The representation of basic operators - holonomies and fluxes - can be derived from the full theory specialized to lattices. With the new methods of this article, loop quantum cosmology comes closer to the full theory and is in a better position to produce reliable predictions when all quantum effects of the theory are taken into account.
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 degeneracy versus cosmography: A cosmographic dark energy model
Luongo, Orlando; Pisani, Giovanni Battista; Troisi, Antonio
In this work, we use cosmography to alleviate the degeneracy among cosmological models, proposing a way to parametrize matter and dark energy in terms of cosmokinematics quantities. The recipe of using cosmography allows to expand observable quantities in Taylor series and to directly compare those expansions with data. The strategy involves the expansions of q and j, up to the second-order around a(t) = 1. This includes additional cosmographic parameters which are fixed by current values of q0 and j0. We therefore propose a fully self-consistent parametrization of the total energy density driving the late-time universe speed up. This stratagem does not remove all the degeneracy but enables one to pass from the model-dependent couple of coefficients, ω0 and Ωm,0, to model-independent quantities determined from cosmography. Afterwards, we describe a feasible cosmographic dark energy model, in which matter is fixed whereas dark energy evolves by means of the cosmographic series. Our technique provides robust constraints on cosmokinematic parameters, permitting one to separately bound matter from dark energy densities. Our cosmographic dark energy model turns out to be one parameter only, but differently from the lambda cold dark matter (ΛCDM) paradigm, it does not contain ansatz on the dark energy form. In addition, we even determine the free parameter of our model in suitable 1σ intervals through Monte Carlo analyses based on the Metropolis algorithm. We compare our results with the standard concordance model and we find that our treatment seems to indicate that dark energy slightly evolves in time, reducing to a pure cosmological constant only as z → 0.
Lemaître Class Dark Energy Model for Relaxing Cosmological Constant
Directory of Open Access Journals (Sweden)
Irina Dymnikova
2017-05-01
Full Text Available Cosmological constant corresponds to the maximally symmetric cosmological term with the equation of state p = − ρ . Introducing a cosmological term with the reduced symmetry, p r = − ρ in the spherically symmetric case, makes cosmological constant intrinsically variable component of a variable cosmological term which describes time-dependent and spatially inhomogeneous vacuum dark energy. Relaxation of the cosmological constant from the big initial value to the presently observed value can be then described in general setting by the spherically symmetric cosmology of the Lemaître class. We outline in detail the cosmological model with the global structure of the de Sitter spacetime distinguished by the holographic principle as the only stable product of quantum evaporation of the cosmological horizon entirely determined by its quantum dynamics. Density of the vacuum dark energy is presented by semiclassical description of vacuum polarization in the spherically symmetric gravitational field, and its initial value is chosen at the GUT scale. The final non-zero value of the cosmological constant is tightly fixed by the quantum dynamics of evaporation and appears in the reasonable agreement with its observational value.
Self-Consistent Modeling of Reionization in Cosmological Hydrodynamical Simulations
Oñorbe, Jose; Lukić, Zarija
2016-01-01
The ultraviolet background (UVB) emitted by quasars and galaxies governs the ionization and thermal state of the intergalactic medium (IGM), regulates the formation of high-redshift galaxies, and is thus a key quantity for modeling cosmic reionization. The vast majority of cosmological hydrodynamical simulations implement the UVB via a set of spatially uniform photoionization and photoheating rates derived from UVB synthesis models. We show that simulations using canonical UVB rates reionize, and perhaps more importantly, spuriously heat the IGM, much earlier z ~ 15 than they should. This problem arises because at z > 6, where observational constraints are non-existent, the UVB amplitude is far too high. We introduce a new methodology to remedy this issue, and generate self-consistent photoionization and photoheating rates to model any chosen reionization history. Following this approach, we run a suite of hydrodynamical simulations of different reionization scenarios, and explore the impact of the timing of ...
A Caveat on Building Nonlocal Models of Cosmology
Tsamis, N C
2014-01-01
Nonlocal models of cosmology might derive from graviton loop corrections to the effective field equations from the epoch of primordial inflation. Although the Schwinger-Keldysh formalism would automatically produce causal and conserved effective field equations, the models so far proposed have been purely phenomenological. Two techniques have been employed to generate causal and conserved field equations: either varying an invariant nonlocal effective action and then enforcing causality by the ad hoc replacement of any advanced Green's function with its retarded counterpart, or else introducing causal nonlocality into a general ansatz for the field equations and then enforcing conservation. We point out here that the two techniques access very different classes of models, and that neither one of them may represent what would actually arise from fundamental theory.
Quintessence models and the cosmological evolution of α
Lee, Seokcheon; Olive, Keith A.; Pospelov, Maxim
2004-10-01
The cosmological evolution of a quintessencelike scalar field ϕ coupled to matter and gauge fields leads to effective modifications of the coupling constants and particle masses over time. We analyze a class of models where the scalar field potential V(ϕ) and the couplings to matter B(ϕ) admit common extremum in ϕ, as in the Damour-Polyakov ansatz. We find that even for the simplest choices of potentials and B(ϕ), the observational constraints on Δα/α coming from quasar absorption spectra, the Oklo phenomenon and Big Bang nucleosynthesis provide complementary constraints on the parameters of the model. We show the evolutionary history of these models in some detail and describe the effects of a varying mass for dark matter.
Quintessence Models and the Cosmological Evolution of alpha
Lee, S; Pospelov, M; Lee, Seokcheon; Olive, Keith A.; Pospelov, Maxim
2004-01-01
The cosmological evolution of a quintessence-like scalar field, phi, coupled to matter and gauge fields leads to effective modifications of the coupling constants and particle masses over time. We analyze a class of models where the scalar field potential V(phi) and the couplings to matter B(phi) admit common extremum in phi, as in the Damour-Polyakov ansatz. We find that even for the simplest choices of potentials and B(phi), the observational constraints on delta alpha/alpha coming from quasar absorption spectra, the Oklo phenomenon and Big Bang nucleosynthesis provide complementary constraints on the parameters of the model. We show the evolutionary history of these models in some detail and describe the effects of a varying mass for dark matter.
Inflation Cosmological Solutions in Two-Dimensional Brans-Dicke Gravity Model
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The purpose of this paper is to study cosmological properties of two-dimensional Brans-Dicke gravity model. For massless scalar field, the new cosmological solutions are found by integration of field equation, these solutions correspond to the inflation solutions with positive cosmological constant. The result of this paper show that the inflation process of universe is controlled by the classical and quantum effect of the scalar field.
Bianchi Type-Ⅲ Cosmological Models with Gravitational Constant G and the Cosmological Constant Λ
Institute of Scientific and Technical Information of China (English)
J.P.Singh; R.K.Tiwari; Pratibha Shukla
2007-01-01
Einstein field equations with variable gravitational and cosmological constants are considered in the presence of perfect fluid for the Bianchi type-Ⅲ universe by assuming conservation law for the energy-momentum tensor.Exact solutions of the field equations are obtained by using the scalar of expansion proportional to the shear scalar θχσ,which leads to a relation between metric potential B=Cn,where n is a constant.The corresponding physical interpretation of the cosmological solutions are also discussed.
Implications of Planck2015 for inflationary, ekpyrotic and anamorphic bouncing cosmologies
Ijjas, Anna; Steinhardt, Paul J.
2016-02-01
The results from Planck2015, when combined with earlier observations from the Wilkinson Microwave Anisotropy Probe, Atacama Cosmology Telescope, South Pole Telescope and other experiments, were the first observations to disfavor the ‘classic’ inflationary paradigm. To satisfy the observational constraints, inflationary theorists have been forced to consider plateau-like inflaton potentials that introduce more parameters and more fine-tuning, problematic initial conditions, multiverse-unpredictability issues, and a new ‘unlikeliness problem’. Some propose turning instead to a ‘postmodern’ inflationary paradigm in which the cosmological properties in our observable Universe are only locally valid and set randomly, with completely different properties (and perhaps even different physical laws) existing in most regions outside our horizon. By contrast, the new results are consistent with the simplest versions of ekpyrotic cyclic models in which the Universe is smoothed and flattened during a period of slow contraction followed by a bounce, and another promising bouncing theory, anamorphic cosmology, has been proposed that can produce distinctive predictions.
Energy Technology Data Exchange (ETDEWEB)
Alexander, Stephon
2003-07-15
We give an overview of the current issues in early universe cosmology and consider the potential resolution of these issues in an as yet nascent spin foam cosmology. The model is the Barrett-Crane Model for quantum gravity along with a generalization of manifold complexes to complexes including conical singularities.
How robust are inflation model and dark matter constraints from cosmological data?
Energy Technology Data Exchange (ETDEWEB)
Hamann, J. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Hannestad, S.; Sloth, M.S. [Aarhus Univ. (Denmark). Dept. of Physics and Astronomy; Wong, Y.Y.Y. [Max-Planck-Institut fuer Physik, Muenchen (Germany). Werner-Heisenberg-Institut
2006-11-15
High-precision data from observation of the cosmic microwave background and the large scale structure of the universe provide very tight constraints on the effective parameters that describe cosmological inflation. Indeed, within a constrained class of {lambda}CDM models, the simple {lambda}{phi}{sup 4} chaotic inflation model already appears to be ruled out by cosmological data. In this paper, we compute constraints on inflationary parameters within a more general framework that includes other physically motivated parameters such as a nonzero neutrino mass. We find that a strong degeneracy between the tensor-to-scalar ratio {tau} and the neutrino mass prevents {lambda}{phi}{sup 4} from being excluded by present data. Reversing the argument, if {lambda}{phi}{sup 4} is the correct model of inflation, it predicts a sum of neutrino masses at 0.3{yields}0.5 eV, a range compatible with present experimental limits and within the reach of the next generation of neutrino mass measurements. We also discuss the associated constraints on the dark matter density, the dark energy equation of state, and spatial curvature, and show that the allowed regions are significantly altered. Importantly, we find an allowed range of 0.094<{omega}{sub c}h{sup 2}<0.136 for the dark matter density, a factor of two larger than that reported in previous studies. This expanded parameter space may have implications for constraints on SUSY dark matter models. (orig.)
An exotic k-essence interpretation of interactive cosmological models
Energy Technology Data Exchange (ETDEWEB)
Forte, Monica [Universidad de Buenos Aires, Departamento de Fisica, Facultad de ciencias Exactas y Naturales, Buenos Aires (Argentina)
2016-01-15
We define a generalization of scalar fields with non-canonical kinetic term which we call exotic k-essence or, briefly, exotik. These fields are generated by the global description of cosmological models with two interactive fluids in the dark sector and under certain conditions they correspond to usual k-essences. The formalism is applied to the cases of constant potential and of inverse square potential and also we develop the purely exotik version for the modified holographic Ricci type (MHR) of dark energy, where the equations of state are not constant. With the kinetic function F = 1 + mx and the inverse square potential we recover, through the interaction term, the identification between k-essences and quintessences of an exponential potential, already known for Friedmann-Robertson-Walker and Bianchi type I geometries. Worked examples are shown that include the self-interacting MHR and also models with crossing of the phantom divide line (PDL). (orig.)
Quintessence a natural model to parametrize the cosmological constant
Macorra, A D L
2003-01-01
We show how a scalar field with gravitational interaction only, i e. quintessence, can account for present day acceleration of the universe and it gives the correct acoustic scale and peaks of the CMP,R anisotropy. We show that the quintessence field can be naturally be described by the fermion condensates of a non-abelian gauge group. This gauge group is unified with the standard model gauge groups. The model has no free parameters. Even the initial energy density at the unification scale and at the condensation scale are fixed by the number of degrees of freedom of the gauge group. We study the evolution of all fields from the unification scale and we calculate the relevant cosmological quantities. (Author)
Modelling neutral hydrogen in galaxies using cosmological hydrodynamical simulations
Duffy, Alan R; Battye, Richard A; Booth, C M; Vecchia, Claudio Dalla; Schaye, Joop
2011-01-01
The characterisation of the atomic and molecular hydrogen content of high-redshift galaxies is a major observational challenge that will be addressed over the coming years with a new generation of radio telescopes. We investigate this important issue by considering the states of hydrogen across a range of structures within high-resolution cosmological hydrodynamical simulations. Additionally, our simulations allow us to investigate the sensitivity of our results to numerical resolution and to sub-grid baryonic physics (especially feedback from supernovae and active galactic nuclei). We find that the most significant uncertainty in modelling the neutral hydrogen distribution arises from our need to model a self-shielding correction in moderate density regions. Future simulations incorporating radiative transfer schemes will be vital to improve on our empirical self-shielding threshold. Irrespective of the exact nature of the threshold we find that while the atomic hydrogen mass function evolves only mildly fro...
Cylindrically symmetric cosmological model of the universe in modified gravity
Mishra, B.; Vadrevu, Samhita
2017-02-01
In this paper, we have constructed the cosmological models of the universe in a cylindrically symmetric space time in two classes of f(R,T) gravity (Harko et al. in Phys. Rev. D 84:024020, 2011). We have discussed two cases: one in the linear form and the other in the quadratic form of R. The matter is considered to be in the form of perfect fluid. It is observed that in the first case, the pressure and energy density remain the same, which reduces to a Zeldovich fluid. In the second case we have studied the quadratic function of f(R,T) gravity in the form f(R)=λ(R+R2) and f(T)=λ T. In the second case the pressure is in the negative domain and the energy density is in the positive domain, which confirms that the equation of state parameter is negative. The physical properties of the constructed models are studied.
Adiabatic density perturbations in a cosmological model with massive neutrinos
Jaroszynski, M.
Lifshitz (1946) has investigated the gravitational instability of a Friedmann Universe model. He treated the matter content of the universe as a single perfect fluid. In other studies, a two fluid approach was used to represent neutrinos and other kinds of matter separately. A distribution function was used by Peebles and Yu (1970), and also by Silk and Wilson (1980) to describe photons of the black-body background during and after the recombination of the primeval plasma. The approach used in the present investigation is similar, except for two differences. No collisional term is used in the kinetic equation, and massive particles are considered. A detailed description is provided of the method used to investigate the gravitational instability of a cosmological model with massive neutrinos. It is pointed out that the obtained results are preliminary. The final spectrum of perturbations is similar to those of Peebles and Yu (1970), and Wilson and Silk (1981).
An exotic k-essence interpretation of interactive cosmological models
Forte, Mónica
2015-01-01
We define a generalization of scalar fields with non-canonical kinetic term which we call exotic k-essence or briefly, exotik. These fields are generated by the global description of cosmological models with two interactive fluids in the dark sector and under certain conditions, they correspond to usual k-essences. The formalism is applied to the cases of constant potential and of inverse square potential and also we develop the purely exotik version for the modified holographic Ricci type of dark energy (MHR), where the equations of state are not constant. With the kinetic function $F=1+mx$ and the inverse square potential we recover, through the interaction term, the identification between k-essences and quintessences of exponential potential, already known for Friedmann-Robertson-Walker and Bianchi type I geometries. Worked examples are shown that include the self-interacting MHR and also models with crossing of the phantom divide line (PDL).
Wang, B.; Abdalla, E.; Atrio-Barandela, F.; Pavón, D.
2016-09-01
Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.
Wang, B; Atrio-Barandela, F; Pavon, D
2016-01-01
Models where Dark Matter and Dark Energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.
Wang, B; Abdalla, E; Atrio-Barandela, F; Pavón, D
2016-09-01
Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.
Spherical collapse model in $f(T)$ cosmologies
Malekjani, M
2016-01-01
In this work, we extend the spherical collapse model (SCM) in the $f(T)$ gravity models. In the context of a specific form of $f(T)$ model, the so-called power law model, we first investigate the background evolution of the universe using the Friedmann Robertson Walker (FRW) metric in a flat geometry. We then follow the linear and non-linear evolutions of the growth of spherical overdensities in perturbation levels. In the linear phase of perturbations, we show that the growth factor of fluctuations depends strongly on the power-law parameter of $f(T)$ model, $b$. We also observe that in the non-linear regime the parameters of SCM depend on the model parameter $b$. We finally compare the predicted number of virialized haloes in the $f(T)$ cosmologies with respect to a concordance $\\Lambda$CDM model and find out that in general the $f(T)$ model with positive (negative) model parameter $b$ has more (less) abundant objects compare to the standard $\\Lambda$CDM universe.
Preon models, relativity, quantum mechanics and cosmology (I)
Gonzalez-Mestres, Luis
2009-01-01
Preons are hypothetic constituents of the standard particles. They were initially assumed to have basically similar properties to those of conventional matter. But this is not necessarily the case: the ultimate constituents of matter may feel a different space-time from that of special relativity and exhibit mechanical properties different from those predicted by standard quantum mechanics. They can also play an important cosmological role (inflation, dark matter, dark energy...). It is even not obvious that energy and momentum would have to be conserved in such a scenario. In this series of papers, we review the subject using the superbradyon model as an example, and suggest new ways to explore possible tests of the preon hypothesis.
Chaubey, R.; Shukla, A. K.; Raushan, Rakesh
2017-04-01
The general class of Bianchi cosmological models with dark energy in the form of modified Chaplygin gas with variable Λ and G and bulk viscosity have been considered. We discuss three types of average scale factor by using a special law for deceleration parameter which is linear in time with negative slope. The exact solutions to the corresponding field equations are obtained. We obtain the solution of bulk viscosity ( ξ), cosmological constant (Λ), gravitational parameter ( G) and deceleration parameter ( q) for different equations of state. The model describes an accelerating Universe for large value of time t, wherein the effective negative pressure induced by Chaplygin gas and bulk viscous pressure are driving the acceleration.
Grieb, Jan Niklas; Sánchez, Ariel G.; Salazar-Albornoz, Salvador; Scoccimarro, Román; Crocce, Martín; Dalla Vecchia, Claudio; Montesano, Francesco; Gil-Marín, Héctor; Ross, Ashley J.; Beutler, Florian; Rodríguez-Torres, Sergio; Chuang, Chia-Hsun; Prada, Francisco; Kitaura, Francisco-Shu; Cuesta, Antonio J.; Eisenstein, Daniel J.; Percival, Will J.; Vargas-Magaña, Mariana; Tinker, Jeremy L.; Tojeiro, Rita; Brownstein, Joel R.; Maraston, Claudia; Nichol, Robert C.; Olmstead, Matthew D.; Samushia, Lado; Seo, Hee-Jong; Streblyanska, Alina; Zhao, Gong-bo
2017-05-01
We extract cosmological information from the anisotropic power-spectrum measurements from the recently completed Baryon Oscillation Spectroscopic Survey (BOSS), extending the concept of clustering wedges to Fourier space. Making use of new fast-Fourier-transform-based estimators, we measure the power-spectrum clustering wedges of the BOSS sample by filtering out the information of Legendre multipoles ℓ > 4. Our modelling of these measurements is based on novel approaches to describe non-linear evolution, bias and redshift-space distortions, which we test using synthetic catalogues based on large-volume N-body simulations. We are able to include smaller scales than in previous analyses, resulting in tighter cosmological constraints. Using three overlapping redshift bins, we measure the angular-diameter distance, the Hubble parameter and the cosmic growth rate, and explore the cosmological implications of our full-shape clustering measurements in combination with cosmic microwave background and Type Ia supernova data. Assuming a Λ cold dark matter (ΛCDM) cosmology, we constrain the matter density to Ω M= 0.311_{-0.010}^{+0.009} and the Hubble parameter to H_0 = 67.6_{-0.6}^{+0.7} km s^{-1 Mpc^{-1}}, at a confidence level of 68 per cent. We also allow for non-standard dark energy models and modifications of the growth rate, finding good agreement with the ΛCDM paradigm. For example, we constrain the equation-of-state parameter to w = -1.019_{-0.039}^{+0.048}. This paper is part of a set that analyses the final galaxy-clustering data set from BOSS. The measurements and likelihoods presented here are combined with others in Alam et al. to produce the final cosmological constraints from BOSS.
Grieb, Jan Niklas; Sánchez, Ariel G.; Salazar-Albornoz, Salvador; Scoccimarro, Román; Crocce, Martín; Dalla Vecchia, Claudio; Montesano, Francesco; Gil-Marín, Héctor; Ross, Ashley J.; Beutler, Florian; Rodríguez-Torres, Sergio; Chuang, Chia-Hsun; Prada, Francisco; Kitaura, Francisco-Shu; Cuesta, Antonio J.; Eisenstein, Daniel J.; Percival, Will J.; Vargas-Magaña, Mariana; Tinker, Jeremy L.; Tojeiro, Rita; Brownstein, Joel R.; Maraston, Claudia; Nichol, Robert C.; Olmstead, Matthew D.; Samushia, Lado; Seo, Hee-Jong; Streblyanska, Alina; Zhao, Gong-bo
2017-01-01
We extract cosmological information from the anisotropic power spectrum measurements from the recently completed Baryon Oscillation Spectroscopic Survey (BOSS), extending the concept of clustering wedges to Fourier space. Making use of new FFT-based estimators, we measure the power spectrum clustering wedges of the BOSS sample by filtering out the information of Legendre multipoles ℓ > 4. Our modelling of these measurements is based on novel approaches to describe non-linear evolution, bias, and redshift-space distortions, which we test using synthetic catalogues based on large-volume N-body simulations. We are able to include smaller scales than in previous analyses, resulting in tighter cosmological constraints. Using three overlapping redshift bins, we measure the angular diameter distance, the Hubble parameter, and the cosmic growth rate, and explore the cosmological implications of our full shape clustering measurements in combination with CMB and SN Ia data. Assuming a ΛCDM cosmology, we constrain the matter density to Ω M= 0.311_{-0.010}^{+0.009} and the Hubble parameter to H_0 = 67.6_{-0.6}^{+0.7} km s^{-1} Mpc^{-1}, at a confidence level (CL) of 68 per cent. We also allow for non-standard dark energy models and modifications of the growth rate, finding good agreement with the ΛCDM paradigm. For example, we constrain the equation-of-state parameter to w = -1.019_{-0.039}^{+0.048}. This paper is part of a set that analyses the final galaxy clustering dataset from BOSS. The measurements and likelihoods presented here are combined with others in Alam et al. (2016) to produce the final cosmological constraints from BOSS.
Torsion gravity with non-minimally coupled fermionic field: some cosmological models
Vignolo, Stefano; Fabbri, Luca
2014-01-01
We investigate some cosmological models arising from a non-minimal coupling of a fermionic field to gravity in the geometrical setting of Einstein-Cartan-Sciama-Kibble gravity. The role played by the non-minimal coupling together with torsion in facing problems such as cosmological singularity, inflation and dark energy is discussed.
A no hair theorem and the problem of initial conditions. [in cosmological model
Jensen, Lars Gerhard; Stein-Schabes, Jaime A.
1987-01-01
It is shown that under very general conditions, any inhomogeneous cosmological model with a positive cosmological constant that can be described in a synchronous reference system will tend asymptotically in time towards the de Sitter solution. This renders the problem of initial conditions less severe.
The effects of a non-zero cosmological constant on the Veltmann models
Lingam, Manasvi
2014-01-01
The Veltmann models, which include the Plummer and Hernquist models as special cases, are studied in the presence of a cosmological constant. Physically relevant quantities such as the velocity dispersion profiles and the anisotropy parameter are computed through the use of the self-consistent approach. The cutoff radii for these models and the mass contained within this volume are also calculated. It is shown that the inclusion of a cosmological constant leads to many observable quantities such as the surface density, dispersion profiles and the anisotropy parameter becoming increasingly modified. In some scenarios, they are easily distinguished from the case where the cosmological constant is absent, as a result of their non-monotonic behaviour. The effects of neighbouring gravitational systems on the central system are also studied, and compared against the effects arising from the cosmological constant. Consequently, it is suggested that the effects of a cosmological constant can prove to be quite importa...
Cosmological implications of the transition from the false vacuum to the true vacuum state
Energy Technology Data Exchange (ETDEWEB)
Stachowski, Aleksander [Jagiellonian University, Astronomical Observatory, Krakow (Poland); Szydlowski, Marek [Jagiellonian University, Astronomical Observatory, Krakow (Poland); Jagiellonian University, Mark Kac Complex Systems Research Centre, Krakow (Poland); Urbanowski, Krzysztof [University of Zielona Gora, Institute of Physics, Zielona Gora (Poland)
2017-06-15
We study cosmology with running dark energy. The energy density of dark energy is obtained from the quantum process of transition from the false vacuum state to the true vacuum state. We use the Breit-Wigner energy distribution function to model the quantum unstable systems and obtain the energy density of the dark energy parametrization ρ{sub de}(t). We also use Krauss and Dent's idea linking properties of the quantum mechanical decay of unstable states with the properties of the observed Universe. In the cosmological model with this parametrization there is an energy transfer between dark matter and dark energy. The intensity of this process, measured by a parameter α, distinguishes two scenarios. As the Universe starts from the false vacuum state, for the small value of α (0 < α < 0.4) it goes through an intermediate oscillatory (quantum) regime of the density of dark energy, while for α > 0.4 the density of the dark energy jumps down. In both cases the present value of the density of dark energy is reached. From a statistical analysis we find this model to be in good agreement with the astronomical data and practically indistinguishable from the ΛCDM model. (orig.)
nIFTy Cosmology: Comparison of Galaxy Formation Models
Knebe, Alexander; Thomas, Peter A; Benson, Andrew; Blaizot, Jeremy; Bower, Richard; Carretero, Jorge; Castander, Francisco J; Cattaneo, Andrea; Cora, Sofia A; Croton, Darren J; Cui, Weiguang; Cunnama, Daniel; De Lucia, Gabriella; Devriendt, Julien E; Elahi, Pascal J; Font, Andreea; Fontanot, Fabio; Garcia-Bellido, Juan; Gargiulo, Ignacio D; Gonzalez-Perez, Violeta; Helly, John; Henriques, Bruno; Hirschmann, Michaela; Lee, Jaehyun; Mamon, Gary A; Monaco, Pierluigi; Onions, Julian; Padilla, Nelson D; Power, Chris; Pujol, Arnau; Skibba, Ramin A; Somerville, Rachel S; Srisawat, Chaichalit; Vega-Martinez, Cristian A; Yi, Sukyoung K
2015-01-01
We present a comparison of 14 galaxy formation models: 12 different semi-analytical models and 2 halo-occupation distribution models for galaxy formation based upon the same cosmological simulation and merger tree information derived from it. The participating codes have proven to be very successful in their own right but they have all been calibrated independently using various observational data sets, stellar models, and merger trees. In this paper we apply them without recalibration and this leads to a wide variety of predictions for the stellar mass function, specific star formation rates, stellar-to- halo mass ratios, and the abundance of orphan galaxies. The scatter is much larger than seen in previous comparison studies primarily because the codes have been used outside of their native environment within which they are well tested and calibrated. The purpose of the `nIFTy comparison of galaxy formation models' is to bring together as many different galaxy formation modellers as possible and to investig...
Cosmological implications of the transition from the false vacuum to the true vacuum state
Stachowski, Aleksander; Urbanowski, Krzysztof
2016-01-01
We study the cosmology with the running dark energy. The parametrization of dark energy with the respect to the redshift is derived from the first principles of quantum mechanics. Energy density of dark energy is obtained from the quantum process of transition from the false vacuum state to the true vacuum state. This is the class of the extended interacting $\\Lambda$CDM models. We consider the energy density of dark energy parametrization $\\rho_\\text{de}(t)$, which follows from the Breit-Wigner energy distribution function which is used to model the quantum unstable systems. The idea that properties of the process of the quantum mechanical decay of unstable states can help to understand the properties of the observed universe was formulated by Krauss and Dent and this idea was used in our considerations. In the cosmological model with the mentioned parametrization there is an energy transfer between the dark matter and dark energy. In such a evolutional scenario the universe is starting from the false vacuum...
Non-gaussianity and Statistical Anisotropy in Cosmological Inflationary Models
Valenzuela-Toledo, Cesar A
2010-01-01
We study the statistical descriptors for some cosmological inflationary models that allow us to get large levels of non-gaussianity and violations of statistical isotropy. Basically, we study two different class of models: a model that include only scalar field perturbations, specifically a subclass of small-field slow-roll models of inflation with canonical kinetic terms, and models that admit both vector and scalar field perturbations. We study the former to show that it is possible to attain very high, including observable, values for the levels of non-gaussianity f_{NL} and \\tao_{NL} in the bispectrum B_\\zeta and trispectrum T_\\zeta of the primordial curvature perturbation \\zeta respectively. Such a result is obtained by taking care of loop corrections in the spectrum P_\\zeta, the bispectrum B_\\zeta and the trispectrum T_\\zeta . Sizeable values for f_{NL} and \\tao_{NL} arise even if \\zeta is generated during inflation. For the latter we study the spectrum P_\\zeta, bispectrum B_\\zeta and trispectrum $T_\\ze...
Bianchi Type-I cosmological mesonic stiff fluid models in Lyra's geometry
Indian Academy of Sciences (India)
S D Katore; S V Thakare; K S Adhao
2008-07-01
Bianchi Type-I cosmological models in Lyra's geometry are obtained when the source of gravitational field is a perfect fluid coupled with massless mesonic scalar field. Some physical and kinematical properties of the models are also discussed.
Jones, Bernard J. T.
2017-04-01
Preface; Notation and conventions; Part I. 100 Years of Cosmology: 1. Emerging cosmology; 2. The cosmic expansion; 3. The cosmic microwave background; 4. Recent cosmology; Part II. Newtonian Cosmology: 5. Newtonian cosmology; 6. Dark energy cosmological models; 7. The early universe; 8. The inhomogeneous universe; 9. The inflationary universe; Part III. Relativistic Cosmology: 10. Minkowski space; 11. The energy momentum tensor; 12. General relativity; 13. Space-time geometry and calculus; 14. The Einstein field equations; 15. Solutions of the Einstein equations; 16. The Robertson–Walker solution; 17. Congruences, curvature and Raychaudhuri; 18. Observing and measuring the universe; Part IV. The Physics of Matter and Radiation: 19. Physics of the CMB radiation; 20. Recombination of the primeval plasma; 21. CMB polarisation; 22. CMB anisotropy; Part V. Precision Tools for Precision Cosmology: 23. Likelihood; 24. Frequentist hypothesis testing; 25. Statistical inference: Bayesian; 26. CMB data processing; 27. Parametrising the universe; 28. Precision cosmology; 29. Epilogue; Appendix A. SI, CGS and Planck units; Appendix B. Magnitudes and distances; Appendix C. Representing vectors and tensors; Appendix D. The electromagnetic field; Appendix E. Statistical distributions; Appendix F. Functions on a sphere; Appendix G. Acknowledgements; References; Index.
TWO ACCURATE TIME-DELAY DISTANCES FROM STRONG LENSING: IMPLICATIONS FOR COSMOLOGY
Energy Technology Data Exchange (ETDEWEB)
Suyu, S. H.; Treu, T. [Department of Physics, University of California, Santa Barbara, CA 93106 (United States); Auger, M. W. [Institute of Astronomy, University of Cambridge, Madingley Rd, Cambridge, CB3 0HA (United Kingdom); Hilbert, S.; Blandford, R. D. [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 452 Lomita Mall, Stanford, CA 94305 (United States); Marshall, P. J. [Department of Physics, University of Oxford, Keble Road, Oxford, OX1 3RH (United Kingdom); Tewes, M.; Courbin, F.; Meylan, G. [Laboratoire d' Astrophysique, Ecole Polytechnique Federale de Lausanne (EPFL), Observatoire de Sauverny, CH-1290 Versoix (Switzerland); Fassnacht, C. D. [Department of Physics, University of California, Davis, CA 95616 (United States); Koopmans, L. V. E. [Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700-AV Groningen (Netherlands); Sluse, D., E-mail: suyu@asiaa.sinica.edu.tw [Argelander-Institut fuer Astronomie, Auf dem Huegel 71, D-53121 Bonn (Germany)
2013-04-01
Strong gravitational lenses with measured time delays between the multiple images and models of the lens mass distribution allow a one-step determination of the time-delay distance, and thus a measure of cosmological parameters. We present a blind analysis of the gravitational lens RXJ1131-1231 incorporating (1) the newly measured time delays from COSMOGRAIL, the COSmological MOnitoring of GRAvItational Lenses, (2) archival Hubble Space Telescope imaging of the lens system, (3) a new velocity-dispersion measurement of the lens galaxy of 323 {+-} 20 km s{sup -1} based on Keck spectroscopy, and (4) a characterization of the line-of-sight structures via observations of the lens' environment and ray tracing through the Millennium Simulation. Our blind analysis is designed to prevent experimenter bias. The joint analysis of the data sets allows a time-delay distance measurement to 6% precision that takes into account all known systematic uncertainties. In combination with the Wilkinson Microwave Anisotropy Probe seven-year (WMAP7) data set in flat wCDM cosmology, our unblinded cosmological constraints for RXJ1131-1231 are H{sub 0}=80.0{sup +5.8}{sub -5.7} km s{sup -1} Mpc{sup -1}, {Omega}{sub de} = 0.79 {+-} 0.03, and w=-1.25{sup +0.17}{sub -0.21}. We find the results to be statistically consistent with those from the analysis of the gravitational lens B1608+656, permitting us to combine the inferences from these two lenses. The joint constraints from the two lenses and WMAP7 are H{sub 0}=75.2{sup +4.4}{sub -4.2} km s{sup -1} Mpc{sup -1}, {Omega}{sub de}=0.76{sup +0.02}{sub -0.03}, and w = -1.14{sup +0.17}{sub -0.20} in flat wCDM, and H{sub 0}=73.1{sup +2.4}{sub -3.6} km s{sup -1} Mpc{sup -1}, {Omega}{sub {Lambda}}=0.75{sup +0.01}{sub -0.02}, and {Omega}{sub k}=0.003{sup +0.005}{sub -0.006} in open {Lambda}CDM. Time-delay lenses constrain especially tightly the Hubble constant H{sub 0} (5.7% and 4.0% respectively in wCDM and open {Lambda}CDM) and curvature of the
Some exact solutions of magnetized viscous model in string cosmology
Indian Academy of Sciences (India)
C P Singh
2014-07-01
In this paper, we study anisotropic Bianchi-V Universe with magnetic field and bulk viscous fluid in string cosmology. Exact solutions of the field equations are obtained by using the equation of state (EoS) for a cloud of strings, and a relationship between bulk viscous coefficient and scalar expansion. The bulk viscous coefficient is assumed to be inversely proportional to the expansion scalar. It is interesting to examine the effects of magnetized bulk viscous string model in early and late stages of evolution of the Universe. This paper presents different string models like geometrical (Nambu string), Takabayasi (p-string) and Reddy string models by taking certain physical conditions. We discuss the nature of classical potential for viscous fluid with and without magnetic field. The presence of bulk viscosity stops the Universe from becoming empty in its future evolution. It is observed that the Universe expands with decelerated rate in the presence of viscous fluid with magnetic field whereas, it expands with marginal inflation in the presence of viscous fluid without magnetic field. The other physical and geometrical aspects of each string model are discussed in detail.
Buchert, Thomas; Wiegand, Alexander
2013-01-01
Kinematical and dynamical properties of a generic inhomogeneous cosmological model, spatially averaged with respect to free-falling (generalized fundamental) observers, are investigated for the matter model `irrotational dust'. Paraphrasing a previous Newtonian investigation, we present a relativistic generalization of a backreaction model based on volume-averaging the `Relativistic Zel'dovich Approximation'. In this model we investigate the effect of `kinematical backreaction' on the evolution of cosmological parameters as they are defined in an averaged inhomogenous cosmology, and we show that the backreaction model interpolates between orthogonal symmetry properties by covering subcases of the plane-symmetric solution, the Lemaitre-Tolman-Bondi solution and the Szekeres solution. We so obtain a powerful model that lays the foundations for quantitatively addressing curvature inhomogeneities as they would be interpreted as `Dark Energy' or `Dark Matter' in a quasi-Newtonian cosmology. The present model, havi...
Darabi, F
2009-01-01
We study a $(4+D)$-dimensional Kaluza-Klein cosmology with a Robertson-Walker type metric having two scale factors $a$ and $R$, corresponding to $D$-dimensional internal space and 4-dimensional universe, respectively. By introducing an exotic matter in the form of perfect fluid with an special equation of state, as the space-time part of the higher dimensional energy-momentum tensor, a four dimensional effective decaying cosmological term appears as $\\lambda \\sim R^{-m}$ with $0 \\leq m\\leq 2$, playing the role of an evolving dark energy in the universe. By taking $m=2$, which has some interesting implications in reconciling observations with inflationary models and is consistent with quantum tunneling, the resulting Einstein's field equations yield the exponential solutions for the scale factors $a$ and $R$. These exponential behaviors may account for the dynamical compactification of extra dimensions and the accelerating expansion of the 4-dimensional universe in terms of Hubble parameter, $H$. The accelerat...
Pozdeeva, Ekaterina O; Toporensky, Alexey V; Vernov, Sergey Yu
2016-01-01
We explore dynamics of cosmological models with bounce solutions evolving on a spatially flat Friedmann-Lemaitre-Robertson-Walker background. We consider cosmological models that contain the Hilbert-Einstein curvature term, the induced gravity term with a negative coupled constant, and even polynomial potentials of the scalar field. Bounce solutions with non-monotonic Hubble parameters have been obtained and analyzed. The case when the scalar field has the conformal coupling and the Higgs potential with an opposite sign is studied in detail. In this model the evolution of the Hubble parameter of the bounce solution essentially depends on the sign of the cosmological constant.
Age Estimates of Universe: from Globular Clusters to Cosmological Models and Probes
Fatima, Hira; Rahman, Syed Faisal Ur
2016-01-01
We performed the photometric analysis of M2 and M92 globular clusters in g and r bands of SLOAN photometric system. We transformed these g and r bands into BV bands of Johnson-Cousins photometric system and built the color magnitude diagram (CMD). We estimated the age, and metallicity of both the clusters, by fitting Padova isochrones of different age and metallicities onto the CMD. We studied Einstein and de Sitter model, bench mark model, the cosmological parameters by WMAP and Planck surveys. Finally, we compared estimated age of globular clusters to the ages from the cosmological models and cosmological parameters values of WMAP and Planck surveys.
Pozdeeva, Ekaterina O.; Skugoreva, Maria A.; Toporensky, Alexey V.; Vernov, Sergey Yu.
2016-12-01
We explore dynamics of cosmological models with bounce solutions evolving on a spatially flat Friedmann-Lemaître-Robertson-Walker background. We consider cosmological models that contain the Hilbert-Einstein curvature term, the induced gravity term with a negative coupled constant, and even polynomial potentials of the scalar field. Bounce solutions with non-monotonic Hubble parameters have been obtained and analyzed. The case when the scalar field has the conformal coupling and the Higgs-like potential with an opposite sign is studied in detail. In this model the evolution of the Hubble parameter of the bounce solution essentially depends on the sign of the cosmological constant.
Bulk viscous cosmological model with interacting dark fluids
Kremer, Gilberto M
2012-01-01
The objective of the present work is to study a cosmological model for a spatially flat Universe whose constituents are a dark energy field and a matter field which includes baryons and dark matter. The constituents are supposed to be in interaction and irreversible processes are taken into account through the inclusion of a non-equilibrium pressure. The non-equilibrium pressure is considered to be proportional to the Hubble parameter within the framework of a first order thermodynamic theory. The dark energy and matter fields are coupled by their barotropic indexes, which are considered as functions of the ratio between their energy densities. The free parameters of the model are adjusted from the best fits of the Hubble parameter data. A comparison of the viscous model with the non-viscous one is performed. It is shown that the equality of the dark energy and matter density parameters and the decelerated-accelerated transition occur at earlier times when the irreversible processes are present. Furthermore, ...
Bulk viscous cosmological model with interacting dark fluids
Energy Technology Data Exchange (ETDEWEB)
Kremer, Gilberto M.; Sobreiro, Octavio A.S., E-mail: kremer@fisica.ufpr.br [Departamento de Fisica, Universidade Federal do Parana, Curitiba, PR (Brazil)
2012-04-15
We study a cosmological model for a spatially flat Universe whose constituents are a dark energy field and a matter field comprising baryons and dark matter. The constituents are assumed to interact with each other, and a non-equilibrium pressure is introduced to account for irreversible processes. We take the nonequilibrium pressure to be proportional to the Hubble parameter within the framework of a first-order thermodynamic theory. The dark energy and matter fields are coupled by their barotropic indexes, which depend on the ratio between their energy densities. We adjust the free parameters of the model to optimize the fits to the Hubble parameter data. We compare the viscous model with the non-viscous one, and show that the irreversible processes cause the dark-energy and matter-density parameters to become equal and the decelerated-accelerated transition to occur at earlier times. Furthermore, the density and deceleration parameters and the distance modulus have the correct behavior, consistent with a viable scenario of the present status of the Universe . (author)
Cosmological models with the spinor and non-minimally interacting scalar field
Osetrin, K E; Rybalov, Yu A
2014-01-01
The solution to the current extending Universe problem, and the description of all stages of evolution compels scientists to consider various cosmological models. Scalar - tensor models are rather simple and also allow us to clearly define the separate stages of evolution. Furthermore, other cosmological models are reduced. Our work takes into consideration the non-minimally interacted scalar field and the spinor field. The spinor field has been considered to establish a better understanding of the stages of evolution in our Universe.
Indian Academy of Sciences (India)
R CHAUBEY; A K SHUKLA; RAKESH RAUSHAN
2017-04-01
The general class of Bianchi cosmological models with dark energy in the form of modified Chaplygin gas with variable $\\Lambda$ and $G$ and bulk viscosity have been considered. We discuss three types of average scalefactor by using a special law for deceleration parameter which is linear in time with negative slope. The exact solutions to the corresponding field equations are obtained. We obtain the solution of bulk viscosity ($\\xi$ ), cosmologicalconstant ($\\Lambda$), gravitational parameter ($G$) and deceleration parameter ($q$) for different equations of state. The model describes an accelerating Universe for large value of time $t$ , wherein the effective negative pressure induced by Chaplygin gas and bulk viscous pressure are driving the acceleration.
Narlikar, Jayant Vishnu
2002-01-01
The third edition of this successful textbook is fully updated and includes important recent developments in cosmology. It begins with an introduction to cosmology and general relativity, and goes on to cover the mathematical models of standard cosmology. The physical aspects of cosmology, including primordial nucleosynthesis, the astroparticle physics of inflation, and the current ideas on structure formation are discussed. Alternative models of cosmology are reviewed, including the model of Quasi-Steady State Cosmology, which has recently been proposed as an alternative to Big Bang Cosmology.
Sanchez, Ariel G; Crocce, Martin; Grieb, Jan Niklas; Salazar-Albornoz, Salvador; DallaVecchia, Claudio; Lippich, Martha; Beutler, Florian; Brownstein, Joel R; Chuang, Chia-Hsun; Eisenstein, Daniel J; Kitaura, Francisco-Shu; Olmstead, Matthew D; Percival, Will J; Prada, Francisco; Rodriguez-Torres, Sergio; Ross, Ashley J; Samushia, Lado; Seo, Hee-Jong; Tinker, Jeremy; Tojeiro, Rita; Vargas-Magana, Mariana; Wang, Yuting; Zhao, Gong-Bo
2016-01-01
We explore the cosmological implications of anisotropic clustering measurements in configuration space of the final galaxy samples from Data Release 12 of the SDSS-III Baryon Oscillation Spectroscopic Survey. We implement a new detailed modelling of the effects of non-linearities, galaxy bias and redshift-space distortions that can be used to extract unbiased cosmological information from our measurements for scales $s \\gtrsim 20\\,h^{-1}{\\rm Mpc}$. We combined the galaxy clustering information from BOSS with the latest cosmic microwave background (CMB) observations and Type Ia supernovae samples and found no significant evidence for a deviation from the $\\Lambda$CDM cosmological model. In particular, these data sets can constrain the dark energy equation of state parameter to $w_{\\rm DE}=-0.996\\pm0.042$ when assumed time-independent, the curvature of the Universe to $\\Omega_{k}=-0.0007\\pm 0.0030$ and the sum of the neutrino masses to $\\sum m_{\
Spectral Action Models of Gravity on Packed Swiss Cheese Cosmology
Ball, Adam
2015-01-01
We present a model of (modified) gravity on spacetimes with fractal structure based on packing of spheres, which are (Euclidean) variants of the Packed Swiss Cheese Cosmology models. As the action functional for gravity we consider the spectral action of noncommutative geometry, and we compute its asymptotic expansion on a space obtained as an Apollonian packing of 3-dimensional spheres inside a 4-dimensional ball. Using information from the zeta function of the Dirac operator of the spectral triple, we show that the leading terms in the asymptotic expansion of the spectral action consist of a zeta regularization of the divergent sum of the leading terms of the spectral actions of the individual spheres in the packing, which accounts for the contribution of the points 1 and 3 in the dimension spectrum (as in the case of a 3-sphere). There is also an additional term coming from the residue at the additional point in the dimension spectrum that corresponds to the packing constant. It detects the fractality of t...
Loop Quantum effects on Om-diagnostic and its Cosmological Implications
Rudra, Prabir
2014-01-01
In this paper we study the Loop quantum effects on the \\textit{Om} diagnostic and subsequently on the universe. We reconstruct the \\textit{Om} diagnostic in the background of Loop quantum gravity and then study the behaviour of various Chaplygin gas dark energy models using the modified diagnostic in a comparative scenario. The trajectories discriminate the various dark energy models from each other both in the Einstein gravity as well as Loop quantum gravity. The Loop quantum effects are also clearly noticeable from the trajectories in past, present and future universe. We see that the Loop quantum deviations are highly pronounced in the early universe, but alleviates as we tend towards the present universe and continue to decay in future. Thus it puts a big question on the effectiveness and consequently the suitability of loop quantum cosmology to explain the future universe.
Bulk flows and CMB dipole anisotropy in cosmological void models
Tomita, K
1999-01-01
The observational behavior of spherically symmetric inhomogeneous cosmological models is studied, which consist of inner and outer homogeneous regions connected by a shell or an intermediate self-similar region. It is assumed that the present matter density parameter in the inner region is smaller than that in the outer region, and the present Hubble parameter in the inner region is larger than that in the outer region. Then galaxies in the inner void-like region can be seen to have a bulk motion relative to matter in the outer region, when we observe them at a point O deviated from the center C of the inner region. Their velocity $v_p$ in the CD direction is equal to the difference of two Hubble parameters multiplied by the distance between C and O. It is found also that the velocity $v_d$ corresponding to CMB dipole anisotropy observed at O is by a factor $\\approx 10$ small compared with $v_p$. This behavior of $v_d$ and $v_p$ may explain the puzzling situation of the cosmic flow of cluster galaxies, when t...
Anisotropic Open Cosmological Models of Spin Matter with Magnetic Moment
Institute of Scientific and Technical Information of China (English)
SHENLi－ming; SUNNai－jiang; 等
2001-01-01
We have derived a set of field equations for a Weyssenhoff spin fluid including magnetic interacton among the spinning particles prevailling in spatially homogeneous,but anisotropically cosmological models of Bianchi type V based on Einstein-Cartan theory.We analyze the field equations in three different equations of states specified by p=1(1/3)ρand p=0,The analytical solutions found are non-singular provided that the combined energy arising from matter spin and magnetic interaction among particles overcomes the anisotropy energy in the Universe,We have also deduced that the minimum particle numers for the radiation(p=(1/3)ρ) and matter(p=0) epochs are 1088 and 10108 respectively.the minimum particle number for the state p=ρ is 1096,leading to the conclusion that we must consider the existence of neutrinos and other creation of particles and anti-particles under torsion and strong gravitational field in the early Universe.
Cosmological perturbations in coherent oscillating scalar field models
Energy Technology Data Exchange (ETDEWEB)
Cembranos, J.A.R.; Maroto, A.L.; Jareño, S.J. Núñez [Departamento de Física Teórica I, Universidad Complutense de Madrid,Avenida Complutense s/n, Madrid (Spain)
2016-03-03
The fact that fast oscillating homogeneous scalar fields behave as perfect fluids in average and their intrinsic isotropy have made these models very fruitful in cosmology. In this work we will analyse the perturbations dynamics in these theories assuming general power law potentials V(ϕ)=λ|ϕ|{sup n}/n. At leading order in the wavenumber expansion, a simple expression for the effective sound speed of perturbations is obtained c{sub eff}{sup 2}=ω=(n−2)/(n+2) with ω the effective equation of state. We also obtain the first order correction in k{sup 2}/ω{sub eff}{sup 2}, when the wavenumber k of the perturbations is much smaller than the background oscillation frequency, ω{sub eff}. For the standard massive case we have also analysed general anharmonic contributions to the effective sound speed. These results are reached through a perturbed version of the generalized virial theorem and also studying the exact system both in the super-Hubble limit, deriving the natural ansatz for δϕ; and for sub-Hubble modes, exploiting Floquet’s theorem.
Cosmological perturbations in coherent oscillating scalar field models
Cembranos, J A R; Jareño, S J Núñez
2015-01-01
The fact that fast oscillating homogeneous scalar fields behave as perfect fluids in average and their intrinsic isotropy have made these models very fruitful in cosmology. In this work we will analyse the perturbations dynamics in these theories assuming general power law potentials $V(\\phi)=\\lambda \\vert\\phi\\vert^{n}/n$. At leading order in the wavenumber expansion, a simple expression for the effective sound speed of perturbations is obtained $c_{\\text{eff}}^2 = \\omega=(n-2)/(n+2)$ with $\\omega$ the effective equation of state. We also obtain the first order correction in $k^2/\\omega_{\\text{eff}}^2$, when the wavenumber $k$ of the perturbations is much smaller than the background oscillation frequency, $\\omega_{\\text{eff}}$. For the standard massive case we have also analysed general anharmonic contributions to the effective sound speed. These results are reached through a perturbed version of the generalized virial theorem and also studying the exact system both in the super-Hubble limit, deriving the nat...
Cosmological perturbations in coherent oscillating scalar field models
Cembranos, J. A. R.; Maroto, A. L.; Jareño, S. J. Núñez
2016-03-01
The fact that fast oscillating homogeneous scalar fields behave as perfect fluids in average and their intrinsic isotropy have made these models very fruitful in cosmology. In this work we will analyse the perturbations dynamics in these theories assuming general power law potentials V( ϕ) = λ| ϕ| n /n. At leading order in the wavenumber expansion, a simple expression for the effective sound speed of perturbations is obtained c eff 2 = ω = ( n - 2)/( n + 2) with ω the effective equation of state. We also obtain the first order correction in k 2/ ω eff 2 , when the wavenumber k of the perturbations is much smaller than the background oscillation frequency, ω eff. For the standard massive case we have also analysed general anharmonic contributions to the effective sound speed. These results are reached through a perturbed version of the generalized virial theorem and also studying the exact system both in the super-Hubble limit, deriving the natural ansatz for δϕ; and for sub-Hubble modes, exploiting Floquet's theorem.
Axially Symmetric Bianchi Type-I Bulk-Viscous Cosmological Models with Time-Dependent and
Indian Academy of Sciences (India)
Nawsad Ali
2013-09-01
The present study deals with spatially homogeneous and anisotropic axially symmetric Bianchi type-I cosmological model with time variable cosmological term in the presence of bulk viscous fluid. The Einstein’s field equations are solved explicitly by time varying deceleration parameter . Consequences of the four cases of phenomenological decay of have been discussed which are consistent with observations. Physical and kinematical parameters of the models are discussed.
$\\psi$ = W e$^{\\pm\\phi}$ quantum cosmological solutions for Class A Bianchi models
Obregón, O
1995-01-01
We find solutions for quantum Class A Bianchi models of the form \\rm \\Psi=W\\, e^{\\pm \\Phi} generalizing the results obtained by Moncrief and Ryan in standard quantum cosmology. For the II and IX Bianchi models there are other solutions \\rm \\tilde\\Phi_2, \\rm \\tilde\\Phi_9 to the Hamilton-Jacobi equation for which \\rm \\Psi is necessarely zero, in contrast with solutions found in supersymmetric quantum cosmology.
Cosmological-constant cold dark matter models and the cobe two-year Sky maps
Bunn, E F; Emory F Bunn; Naoshi Sugiyama
1994-01-01
Abstract. We compare the two-year COBE DMR sky maps with the predictions of cosmological-constant cold dark matter models. Using a Bayesian analysis, we find that the most likely value of the cosmological constant in such a model is Lambda = 0. The data set an upper limit on Lambda of 0.71 (0.78) at 90% confidence, and 0.78 (0.86) at 95% confidence with (without) the quadrupole anisotropy.
Exact solutions of a Flat Full Causal Bulk viscous FRW cosmological model through factorization
Cornejo-Pérez, O
2012-01-01
We study the classical flat full causal bulk viscous FRW cosmological model through the factorization method. The method allows to find some new exact parametric solutions for different values of the viscous parameter $s$. Special attention is given to the well known case $s=1/2$, for which the cosmological model admits scaling symmetries. Also, some exact parametric solutions for $s=1/2$ are obtained through the Lie group method.
Simple inflationary models in Gauss-Bonnet brane-world cosmology
Okada, Nobuchika; Okada, Satomi
2016-06-01
In light of the recent Planck 2015 results for the measurement of the cosmic microwave background (CMB) anisotropy, we study simple inflationary models in the context of the Gauss-Bonnet (GB) brane-world cosmology. The brane-world cosmological effect modifies the power spectra of scalar and tensor perturbations generated by inflation and causes a dramatic change for the inflationary predictions of the spectral index (n s) and the tensor-to-scalar ratio (r) from those obtained in the standard cosmology. In particular, the predicted r values in the inflationary models favored by the Planck 2015 results are suppressed due to the GB brane-world cosmological effect, which is in sharp contrast with inflationary scenario in the Randall-Sundrum brane-world cosmology, where the r values are enhanced. Hence, these two brane-world cosmological scenarios are distinguishable. With the dramatic change of the inflationary predictions, the inflationary scenario in the GB brane-world cosmology can be tested by more precise measurements of n s and future observations of the CMB B-mode polarization.
Energy Technology Data Exchange (ETDEWEB)
Ho, Shirley; White, Martin; Schlegel, David J.; Seljak, Uros; Reid, Beth [Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, MS 50R-5045, Berkeley, CA 94720 (United States); Cuesta, Antonio; Padmanabhan, Nikhil [Yale Center for Astronomy and Astrophysics, Yale University, New Haven, CT 06511 (United States); Seo, Hee-Jong [Berkeley Center for Cosmological Physics, LBL and Department of Physics, University of California, Berkeley, CA 94720 (United States); De Putter, Roland [ICC, University of Barcelona (IEEC-UB), Marti i Franques 1, E-08028 Barcelona (Spain); Ross, Ashley J.; Percival, Will J. [Institute of Cosmology and Gravitation, Dennis Sciama Building, University of Portsmouth, Portsmouth PO1 3FX (United Kingdom); Saito, Shun [Department of Astronomy, University of California Berkeley, CA (United States); Schlafly, Eddie [Department of Astronomy, Harvard University, 60 Garden St. MS 20, Cambridge, MA 02138 (United States); Hernandez-Monteagudo, Carlos [Centro de Estudios de Fisica del Cosmos de Aragon (CEFCA), Plaza de San Juan 1, planta 2, E-44001 Teruel (Spain); Sanchez, Ariel G. [Max-Planck-Institut fuer Extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching (Germany); Blanton, Michael [Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, New York, NY 10003 (United States); Skibba, Ramin [Steward Observatory, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721 (United States); Schneider, Don [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Mena, Olga [Instituto de Fisica Corpuscular, Universidad de Valencia-CSIC (Spain); Viel, Matteo, E-mail: cwho@lbl.gov [INAF-Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, I-34131 Trieste (Italy); and others
2012-12-10
The Sloan Digital Sky Survey (SDSS) surveyed 14,555 deg{sup 2}, and delivered over a trillion pixels of imaging data. We present a study of galaxy clustering using 900,000 luminous galaxies with photometric redshifts, spanning between z = 0.45 and z = 0.65, constructed from the SDSS using methods described in Ross et al. This data set spans 11,000 deg{sup 2} and probes a volume of 3 h {sup -3} Gpc{sup 3}, making it the largest volume ever used for galaxy clustering measurements. We describe in detail the construction of the survey window function and various systematics affecting our measurement. With such a large volume, high-precision cosmological constraints can be obtained given careful control and understanding of the observational systematics. We present a novel treatment of the observational systematics and its applications to the clustering signals from the data set. In this paper, we measure the angular clustering using an optimal quadratic estimator at four redshift slices with an accuracy of {approx}15%, with a bin size of {delta}{sub l} = 10 on scales of the baryon acoustic oscillations (BAOs; at l {approx} 40-400). We also apply corrections to the power spectra due to systematics and derive cosmological constraints using the full shape of the power spectra. For a flat {Lambda}CDM model, when combined with cosmic microwave background Wilkinson Microwave Anisotropy Probe 7 (WMAP7) and H{sub 0} constraints from using 600 Cepheids observed by Wide Field Camera 3 (WFC3; HST), we find {Omega}{sub {Lambda}} = 0.73 {+-} 0.019 and H{sub 0} to be 70.5 {+-} 1.6 s{sup -1} Mpc{sup -1} km. For an open {Lambda}CDM model, when combined with WMAP7 + HST, we find {Omega}{sub K} = 0.0035 {+-} 0.0054, improved over WMAP7+HST alone by 40%. For a wCDM model, when combined with WMAP7+HST+SN, we find w = -1.071 {+-} 0.078, and H{sub 0} to be 71.3 {+-} 1.7 s{sup -1} Mpc{sup -1} km, which is competitive with the latest large-scale structure constraints from large spectroscopic
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.
Ryan, M.
1972-01-01
The study of cosmological models by means of equations of motion in Hamiltonian form is considered. Hamiltonian methods applied to gravity seem to go back to Rosenfeld (1930), who constructed a quantum-mechanical Hamiltonian for linearized general relativity theory. The first to notice that cosmologies provided a simple model in which to demonstrate features of Hamiltonian formulation was DeWitt (1967). Applications of the ADM formalism to homogeneous cosmologies are discussed together with applications of the Hamiltonian formulation, giving attention also to Bianchi-type universes. Problems involving the concept of superspace and techniques of quantization are investigated.
Implications of Planck2015 for inflationary, ekpyrotic and anamorphic bouncing cosmologies
Ijjas, Anna
2015-01-01
The results from Planck2015, when combined with earlier observations from WMAP, ACT, SPT and other experiments, were the first observations to disfavor the "classic" inflationary paradigm. To satisfy the observational constraints, inflationary theorists have been forced to consider plateau-like inflaton potentials that introduce more parameters and more fine-tuning, problematic initial conditions, multiverse-unpredictability issues, and a new 'unlikeliness problem.' Some propose turning instead to a "postmodern" inflationary paradigm in which the cosmological properties in our observable universe are only locally valid and set randomly, with completely different properties (and perhaps even different physical laws) existing in most regions outside our horizon. By contrast, the new results are consistent with the simplest versions of ekpyrotic cyclic models in which the universe is smoothed and flattened during a period of slow contraction followed by a bounce, and another promising bouncing theory, anamorphic...
The Era of Massive Population III Stars: Cosmological Implications and Self-Termination
Yoshida, N; Hernquist, L; Yoshida, Naoki; Bromm, Volker; Hernquist, Lars
2004-01-01
The birth and death of the first generation of stars have important implications for the thermal state and chemical properties of the intergalactic medium (IGM) in the early universe. Sometime after recombination, the neutral, chemically pristine gas was reionized by ultraviolet photons emitted from the first stars, but also enriched with heavy elements when these stars ended their lives as energetic supernovae. Using the results from high-resolution cosmological simulations of early structure formation that include radiative transfer, we show that a significant volume fraction of the IGM can be metal-polluted, as well as ionized, by massive Population III stars formed in small-mass (10^6-10^7 Msun) halos early on. If most of the early generation stars die as pair-instability supernovae with energies up to 10^{53} ergs, the volume-averaged mean metallicity will quickly reach Z ~ 10^{-4}Zsun by a redshift of 15-20, possibly causing a prompt transition to the formation of a stellar population that is dominated ...
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.
Coasting cosmologies with time dependent cosmological constant
Pimentel, L O; Pimentel, Luis O.
1999-01-01
The effect of a time dependent cosmological constant is considered in a family of scalar tensor theories. Friedmann-Robertson-Walker cosmological models for vacumm and perfect fluid matter are found. They have a linear expansion factor, the so called coasting cosmology, the gravitational "constant" decreace inversely with time; this model satisfy the Dirac hipotesis. The cosmological "constant" decreace inversely with the square of time, therefore we can have a very small value for it at present time.
Dănilă, Bogdan; Mak, Man Kwong; Pantaragphong, Praiboon; Sabau, Sorin
2016-01-01
We perform the study of the stability of the cosmological scalar field models, by using the Jacobi stability analysis, or the Kosambi-Cartan-Chern (KCC) theory. In the KCC approach we describe the time evolution of the scalar field cosmologies in geometric terms, by performing a "second geometrization", by considering them as paths of a semispray. By introducing a non-linear connection and a Berwald type connection associated to the Friedmann and Klein-Gordon equations, five geometrical invariants can be constructed, with the second invariant giving the Jacobi stability of the cosmological model. We obtain all the relevant geometric quantities, and we formulate the condition of the Jacobi stability for scalar field cosmologies in the second order formalism. As an application of the developed methods we consider the Jacobi stability properties of the scalar fields with exponential and Higgs type potential. We find that the Universe dominated by a scalar field exponential potential is in Jacobi unstable state, ...
Theories of modified gravity and reconstruction schemes of cosmological models
López Revelles, Antonio Jesús
2013-01-01
[spa] En esta memoria de tesis se expone el trabajo llevado a cabo por el doctorando durante los últimos cuatro años, el cual versa principalmente sobre diversos aspectos de soluciones cosmológicas obtenidas a partir de teorías de gravedad modificada. Para entender el origen y la importancia de las teorías de gravedad modificada es necesario comentar antes algunos hechos acontecidos durante el siglo XX en el marco de la cosmología. La cosmología como ciencia nació gracias a la Teoría de la Re...
Energy Technology Data Exchange (ETDEWEB)
Nugent, Peter E; Ellis, R.S.; Sullivan, M.; Nugent, P.E.; Howell, D.A.; Gal-Yam, A.; Astier, P.; Balam, D.; Balland, C.; Basa, S.; Carlberg, R.; Conley, A.; Fouchez, D.; Guy, J.; Hardin, D.; Hook, I.; Pain, R.; Perrett, K.; Pritchet, C.J.; Regnault, N.
2008-02-28
We analyze the mean rest-frame ultraviolet (UV) spectrum of Type Ia Supernovae (SNe) and its dispersion using high signal-to-noise ratio Keck-I/LRIS-B spectroscopy for a sample of 36 events at intermediate redshift (z=0.5) discovered by the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). We introduce a new method for removing host galaxy contamination in our spectra, exploiting the comprehensive photometric coverage of the SNLS SNe and their host galaxies, thereby providing the first quantitative view of the UV spectral properties of a large sample of distant SNe Ia. Although the mean SN Ia spectrum has not evolved significantly over the past 40percent of cosmic history, precise evolutionary constraints are limited by the absence of a comparable sample of high-quality local spectra. The mean UV spectrum of our z~;;=0.5 SNe Ia and its dispersion is tabulated for use in future applications. Within the high-redshift sample, we discover significant UV spectral variations and exclude dust extinction as the primary cause by examining trends with the optical SN color. Although progenitor metallicity may drive some of these trends, the variations we see are much larger than predicted in recent models and do not follow expected patterns. An interesting new result is a variation seen in the wavelength of selected UV features with phase. We also demonstrate systematic differences in the SN Ia spectral features with SN light curve width in both the UV and the optical. We show that these intrinsic variations could represent a statistical limitation in the future use of high-redshift SNe Ia for precision cosmology. We conclude that further detailed studies are needed, both locally and at moderate redshift where the rest-frame UV can be studied precisely, in order that future missions can confidently be planned to fully exploit SNe Ia as cosmological probes.
Cosmological models with spinor and scalar fields by Noether symmetry approach
Kremer, Gilberto M
2013-01-01
General cosmological models with spinor and scalar fields playing the role of gravitational sources are analyzed. The Noether symmetry approach is taken as a criterion to constrain the undefined potentials and couplings of the generic actions. For all the found Noether symmetries the corresponding dynamical systems can be analytically integrated. The obtained cosmological solutions describe the early and late Universe as expected by basing on the known eras of the Universe.
Interacting dark energy models in Cosmology and large-scale structure observational tests
Rafael José França Marcondes
2016-01-01
Modern Cosmology offers us a great understanding of the universe with striking precision, made possible by the modern technologies of the newest generations of telescopes. The standard cosmological model, however, is not absent of theoretical problems and open questions. One possibility that has been put forward is the existence of a coupling between dark sectors. The idea of an interaction between the dark components could help physicists understand why we live in an epoch of the universe wh...
Baryonic effects on weak-lensing two-point statistics and its cosmological implications
Mohammed, Irshad; Teyssier, Romain; Amara, Adam
2014-01-01
We develop an extension of \\textit{the Halo Model} that describes analytically the corrections to the matter power spectrum due to the physics of baryons. We extend these corrections to the weak-lensing shear angular power spectrum. Within each halo, our baryonic model accounts for: 1) a central galaxy, the major stellar component whose properties are derived from abundance matching techniques; 2) a hot plasma in hydrostatic equilibrium and 3) an adiabatically-contracted dark matter component. This analytic approach allows us to compare our model to the dark-matter-only case. Our basic assumptions are tested against the hydrodynamical simulations of Martizzi et. al. (2014), with which a remarkable agreement is found. Our baryonic model has only one free parameter, $M_{\\rm crit}$, the critical halo mass that marks the transition between feedback-dominated halos, mostly devoid of gas, and gas rich halos, in which AGN feedback effects become weaker. We explore the entire cosmological parameter space, using the a...
Sterile neutrino constraints from cosmology
DEFF Research Database (Denmark)
Hamann, Jan; Hannestad, Steen; Raffelt, Georg G.
2012-01-01
The presence of light particles beyond the standard model's three neutrino species can profoundly impact the physics of decoupling and primordial nucleosynthesis. I review the observational signatures of extra light species, present constraints from recent data, and discuss the implications...... of possible sterile neutrinos with O(eV)-masses for cosmology....
Dynamics of gravitating hadron matter in Bianchi-IX cosmological model
Pavluchenko, Sergey A
2016-01-01
We perform an analysis of the Einstein-Skyrme cosmological model in Bianchi-IX background. We analytically describe asymptotic regimes and semi-analytically -- generic regimes. It appears that depending on the product of Newtonian constant $\\kappa$ with Skyrme coupling $K$, in absence of the cosmological term there are three regimes possible -- recollapse with $\\kK 2$. In presence of the positive cosmological term, power-law regimes turn to exponential (de Sitter) ones while recollapse regime turn to exponential if the value for $\\Lambda$-term is sufficiently large, otherwise the regime remains recollapse. Negative cosmological term leads to the recollapse regardless of $\\kK$. All nonsingular regimes have the squashing coefficient $a(t) \\to 1$ at late times, which is associated with restoring symmetry dynamics. Also all nonsingular regimes appear to be linearly stable -- exponential solutions always while power-law for an open region of initial conditions.
Dynamical system of scalar field from 2-dimension to 3-D and its cosmological implications
Energy Technology Data Exchange (ETDEWEB)
Fang, Wei [Shanghai Normal University, Department of Physics, Shanghai (China); The Shanghai Key Lab for Astrophysics, Shanghai (China); Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States); Tu, Hong [Shanghai Normal University, Department of Physics, Shanghai (China); The Shanghai Key Lab for Astrophysics, Shanghai (China); Huang, Jiasheng [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States); Shu, Chenggang [The Shanghai Key Lab for Astrophysics, Shanghai (China)
2016-09-15
We give the three-dimensional dynamical autonomous systems for most of the popular scalar field dark energy models including (phantom) quintessence, (phantom) tachyon, K-essence, and general non-canonical scalar field models, change the dynamical variables from variables (x, y, λ) to observable related variables (w{sub φ}, Ω{sub φ}, λ), and show the intimate relationships between those scalar fields that the three-dimensional system of K-essence can reduce to (phantom) tachyon, general non-canonical scalar field can reduce to (phantom) quintessence and K-essence can also reduce to (phantom) quintessence for some special cases. For the applications of the three-dimensional dynamical systems, we investigate several special cases and give the exactly dynamical solutions in detail. In the end of this paper, we argue that it is more convenient and also has more physical meaning to express the differential equations of dynamical systems in (w{sub φ}, Ω{sub φ}, λ) instead of variables (x, y, λ) and to investigate the dynamical system in three dimensions instead of two dimensions. We also raise a question about the possibility of the chaotic behavior in the spatially flat single scalar field FRW cosmological models in the presence of ordinary matter. (orig.)
Dynamical system of scalar field from 2-dimension to 3-D and its cosmological implications
Fang, Wei; Tu, Hong; Huang, Jiasheng; Shu, Chenggang
2016-09-01
We give the three-dimensional dynamical autonomous systems for most of the popular scalar field dark energy models including (phantom) quintessence, (phantom) tachyon, K-essence, and general non-canonical scalar field models, change the dynamical variables from variables (x, y, λ ) to observable related variables (w_{φ }, Ω _{φ }, λ ), and show the intimate relationships between those scalar fields that the three-dimensional system of K-essence can reduce to (phantom) tachyon, general non-canonical scalar field can reduce to (phantom) quintessence and K-essence can also reduce to (phantom) quintessence for some special cases. For the applications of the three-dimensional dynamical systems, we investigate several special cases and give the exactly dynamical solutions in detail. In the end of this paper, we argue that it is more convenient and also has more physical meaning to express the differential equations of dynamical systems in (w_{φ }, Ω _{φ }, λ ) instead of variables (x, y, λ ) and to investigate the dynamical system in three dimensions instead of two dimensions. We also raise a question about the possibility of the chaotic behavior in the spatially flat single scalar field FRW cosmological models in the presence of ordinary matter.
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.
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.
Exact Solution and Exotic Fluid in Cosmology
Directory of Open Access Journals (Sweden)
Phillial Oh
2012-09-01
Full Text Available We investigate cosmological consequences of nonlinear sigma model coupled with a cosmological fluid which satisfies the continuity equation. The target space action is of the de Sitter type and is composed of four scalar fields. The potential which is a function of only one of the scalar fields is also introduced. We perform a general analysis of the ensuing cosmological equations and give various critical points and their properties. Then, we show that the model exhibits an exact cosmological solution which yields a transition from matter domination into dark energy epoch and compare it with the Λ-CDM behavior. Especially, we calculate the age of the Universe and show that it is consistent with the observational value if the equation of the state ωf of the cosmological fluid is within the range of 0.13 < ωf < 0.22. Some implication of this result is also discussed.
Bianchi Type-IX viscous fluid cosmological model in general relativity
Indian Academy of Sciences (India)
Raj Bali; Mahesh Kumar Yadav
2005-02-01
Bianchi Type-IX viscous fluid cosmological model is investigated. To get a deterministic model, we have assumed the condition = ( is a constant) between metric potentials and where is the coefficient of shear viscosity and the scalar of expansion in the model. The coefficient of bulk viscosity () is taken as constant. The physical and geometrical aspects of the model are also discussed.
Khurshudyan, M; Momeni, D; Myrzakulov, R; Raza, M
2014-01-01
The subject of this paper is to investigate the weak regime covariant scalar-tensor-vector gravity (STVG) theory, known as the MOdified gravity (MOG) theory of gravity. First, we show that the MOG in the absence of scalar fields is converted into $\\Lambda(t),G(t)$ models. Time evolution of the cosmological parameters for a family of viable models have been investigated. Numerical results with the cosmological data have been adjusted. We've introduced a model for dark energy (DE) density and cosmological constant which involves first order derivatives of Hubble parameter. To extend this model, correction terms including the gravitational constant are added. In our scenario, the cosmological constant is a function of time. To complete the model,interaction terms between dark energy and dark matter (DM) manually entered in phenomenological form. Instead of using the dust model for DM, we have proposed DM equivalent to a barotropic fluid. Time evolution of DM is a function of other cosmological parameters. Using ...
Cosmological evolution in a two-brane warped geometry model
Directory of Open Access Journals (Sweden)
Sumit Kumar
2015-07-01
Full Text Available We study an effective 4-dimensional scalar–tensor field theory, originated from an underlying brane–bulk warped geometry, to explore the scenario of inflation. It is shown that the inflaton potential naturally emerges from the radion energy–momentum tensor which in turn results in an inflationary model of the Universe on the visible brane that is consistent with the recent results from the Planck's experiment. The dynamics of modulus stabilization from the inflaton rolling condition is demonstrated. The implications of our results in the context of recent BICEP2 results are also discussed.
Cosmological evolution in a two-brane warped geometry model
Energy Technology Data Exchange (ETDEWEB)
Kumar, Sumit, E-mail: sumit@ctp-jamia.res.in [Center For Theoretical Physics, Jamia Millia Islamia, New Delhi 110025 (India); Sen, Anjan A., E-mail: aasen@jmi.ac.in [Center For Theoretical Physics, Jamia Millia Islamia, New Delhi 110025 (India); SenGupta, Soumitra, E-mail: tpssg@iacs.res.in [Department of Theoretical Physics, Indian Association for the Cultivation of Science, Kolkata 700032 (India)
2015-07-30
We study an effective 4-dimensional scalar–tensor field theory, originated from an underlying brane–bulk warped geometry, to explore the scenario of inflation. It is shown that the inflaton potential naturally emerges from the radion energy–momentum tensor which in turn results in an inflationary model of the Universe on the visible brane that is consistent with the recent results from the Planck's experiment. The dynamics of modulus stabilization from the inflaton rolling condition is demonstrated. The implications of our results in the context of recent BICEP2 results are also discussed.
Cosmological evolution in a two-brane warped geometry model
Kumar, Sumit; SenGupta, Soumitra
2014-01-01
We study an effective 4-dimensional scalar-tensor field theory, originated from an underlying brane-bulk warped geometry, to explore the scenario of inflation. It is shown that the inflaton potential naturally emerges from the radion energy-momentum tensor which in turn results into an inflationary model of the Universe on the visible brane that is consistent with the recent results from the Planck's experiment. The dynamics of modulus stabilization from the inflaton rolling condition is demonstrated. The implications of our results in the context of recent BICEP2 results are also discussed.
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.
Simple inflationary models in Gauss-Bonnet brane-world cosmology
Okada, Nobuchika
2014-01-01
In light of the recent measurements of the CMB anisotropy by the WMAP and Planck satellite experiments and the observation of CMB $B$-mode polarization announced by the BICEP2 collaboration, we study simple inflationary models in the context of the Gauss-Bonnet brane-world cosmology. The brane-world cosmological effect modifies the power spectra of scalar and tensor perturbations generated by inflation and causes a dramatic change for the inflationary predictions of the spectral index ($n_s$) and the tensor-to-scalar ratio ($r$) from those obtained in the standard cosmology. In particular, the power spectrum of tensor perturbation is suppressed due to the Gauss-Bonnet brane-world cosmological effect, which is in sharp contrast with inflationary scenario in the Randall-Sundrum brane-world cosmology where the power spectrum is enhanced. Hence, these two brane-world cosmological scenarios are distinguishable. With the dramatic change of the inflationary predictions, the inflationary scenario in the Gauss-Bonnet ...
Homoclinic Chaos in Axisymmetric Bianchi-IX cosmological models with an "ad hoc" quantum potential
Corrêa, G. C.; Stuchi, T. J.; Jorás, S. E.
2010-01-01
In this work we study the dynamics of the axisymmetric Bianchi IX cosmological model with a term of quantum potential added. As it is well known this class of Bianchi IX models are homogeneous and anisotropic with two scale factors, $A(t)$ and $B(t)$, derived from the solution of Einstein's equation for General Relativity. The model we use in this work has a cosmological constant and the matter content is dust. To this model we add a quantum-inspired potential that is intended to represent sh...
A Review on the Cosmology of the de Sitter Horndeski Models
Directory of Open Access Journals (Sweden)
Nelson J. Nunes
2017-03-01
Full Text Available We review the most general scalar-tensor cosmological models with up to second-order derivatives in the field equations that have a fixed spatially flat de Sitter critical point independent of the material content or vacuum energy. This subclass of the Horndeski Lagrangian is capable of dynamically adjusting any value of the vacuum energy of the matter fields at the critical point. We present the cosmological evolution of the linear models and the non-linear models with shift symmetry. We come to the conclusion that the shift symmetric non-linear models can deliver a viable background compatible with current observations.
Observing the inflation potential. [in models of cosmological inflation
Copeland, Edmund J.; Kolb, Edward W.; Liddle, Andrew R.; Lidsey, James E.
1993-01-01
We show how observations of the density perturbation (scalar) spectrum and the gravitational wave (tensor) spectrum allow a reconstruction of the potential responsible for cosmological inflation. A complete functional reconstruction or a perturbative approximation about a single scale are possible; the suitability of each approach depends on the data available. Consistency equations between the scalar and tensor spectra are derived, which provide a powerful signal of inflation.
Nonparametric test of consistency between cosmological models and multiband CMB measurements
Aghamousa, Amir
2015-01-01
We present a novel approach to test the consistency of the cosmological models with multiband CMB data using a nonparametric approach. In our analysis we calibrate the REACT (Risk Estimation and Adaptation after Coordinate Transformation) confidence levels associated with distances in function space (confidence distances) based on the Monte Carlo simulations in order to test the consistency of an assumed cosmological model with observation. To show the applicability of our algorithm, we confront Planck 2013 temperature data with concordance model of cosmology considering two different Planck spectra combination. In order to have an accurate quantitative statistical measure to compare between the data and the theoretical expectations, we calibrate REACT confidence distances and perform a bias control using many realizations of the data. Our results in this work using Planck 2013 temperature data put the best fit $\\Lambda$CDM model at $95\\% (\\sim 2\\sigma)$ confidence distance from the center of the nonparametri...
Amruth, B R; R., Amruth B.; Patwardhan, Ajay
2006-01-01
Cosmological inflation models with modifications to include recent cosmological observations has been an active area of research after WMAP 3 results, which have given us information about the composition of dark matter, normal matter and dark energy and the anisotropy at the 300,000 years horizon with high precision. We work on inflation models of Guth and Linde and modify them by introducing a doublet scalar field to give normal matter particles and their supersymmetric partners which result in normal and dark matter of our universe. We include the cosmological constant term as the vaccuum expectation value of the stress energy tensor, as the dark energy. We callibrate the parameters of our model using recent observations of density fluctuations. We develop a model which consistently fits with the recent observations.
Bianchi Type Ⅲ Bulk Viscous Barotropic Fluid Cosmological Models with Variable G and A
Institute of Scientific and Technical Information of China (English)
Raj Ba-li; Seema Tinker
2009-01-01
Bianchi type-Ⅲ bulk viscous barotropic fluid cosmological model with variables G and A is investigated. To obtainthe realistic model, we assume the conditions between the metric potentials A, B, C as A/A = B/B = m1/tnand C/C = m2/tn, P = p - 3ηH, η= ηops, p =γp, 0 γ 1, where p is isotropic pressure, η the coefficient of bulk viscosity, ηo and S the constants, H the Hubble constant, m1= 2m2 where m1 0, m2 0. The solutions obtained lead to inflationary phase and the results obtained match with the observations. The case n = 1 for S = 1 is also discussed, relating the results with the observations.PACS: 98. 80. Hω, 04.50. +h, 98.80. CqSpatially homogeneous and anisotropic cosmologi-cal models play a significant role in description of the large scale behaviour of the universe. The choice of anisotropic model in the Einstein system of field equa-tions permits us to obtain cosmological model more general than the Robertson-Walker model. Tikekar and Patel[1] have investigated some exact solutions of massive string for Bianchi type-Ⅲ spacetime in the presence and absence of magnetic field. They have also discussed the behaviour of the model in the ab-sence of magnetic field. Bali and Dave[2] investigated the Bianchi type-Ⅲ string cosmological model with bulk viscosity. Recently Bali and Pradhan[3] investi-gated the Bianchi type-Ⅲ string cosmological models with time-dependent bulk viscosity.
Tilted Bianchi type I dust ﬂuid cosmological model in general relativity
Indian Academy of Sciences (India)
Raj Bali; Keshav Sharma
2002-03-01
In this paper, we have investigated a tilted Bianchi type I cosmological model ﬁlled with dust of perfect ﬂuid in general relativity. To get a determinate solution, we have assumed a condition = between metric potentials. The physical and geometrical aspects of the model together with singularity in the model are also discussed.
Roy, S. R.; Banerjee, S. K.
1992-11-01
A homogeneous Bianchi type VIh cosmological model filled with perfect fluid, null electromagnetic field and streaming neutrinos is obtained for which the free gravitational field is of the electric type. The barotropic equation of statep = (γ-1)ɛ is imposed in the particular case of Bianchi VI0 string models. Various physical and kinematical properties of the models are discussed.
Indian Academy of Sciences (India)
G P Singh; R V Deshpande; T Singh
2004-11-01
We have studied five-dimensional homogeneous cosmological models with variable and bulk viscosity in Lyra geometry. Exact solutions for the field equations have been obtained and physical properties of the models are discussed. It has been observed that the results of new models are well within the observational limit.
The B-L Phase Transition: Implications for Cosmology and Neutrinos
Schmitz, Kai
2013-01-01
We investigate the possibility that the hot thermal phase of the early universe is ignited in consequence of the B-L phase transition, which represents the cosmological realization of the spontaneous breaking of the Abelian gauge symmetry associated with B-L, the difference between baryon number B and lepton number L. Prior to the B-L phase transition, the universe experiences a stage of hybrid inflation. Towards the end of inflation, the false vacuum of unbroken B-L decays, which entails tachyonic preheating as well as the production of cosmic strings. The dynamics of the B-L breaking Higgs field and the B-L gauge degrees of freedom, in combination with thermal processes, generate an abundance of heavy (s)neutrinos. These (s)neutrinos decay into radiation, thereby reheating the universe, generating the baryon asymmetry of the universe and setting the stage for the thermal production of gravitinos. We study the B-L phase transition in the full supersymmetric Abelian Higgs model, for which we derive and discus...
Ho, Shirley; Seo, Hee-Jong; de Putter, Roland; Ross, Ashley J; White, Martin; Padmanabhan, Nikhil; Saito, Shun; Schlegel, David J; Schlafly, Eddie; Seljak, Uros; Hernandez-Monteagudo, Carlos; Sanchez, Ariel G; Percival, Will J; Blanton, Michael; Skibba, Ramin; Schneider, Don; Reid, Beth; Mena, Olga; Viel, Matteo; Eisenstein, Daniel J; Prada, Francisco; Weaver, Benjamin; Bahcall, Neta; Bizyaev, Dimitry; Brewinton, Howard; Brinkman, Jon; da Costa, Luiz Nicolaci; Gott, John R; Malanushenko, Elena; Malanushenko, Viktor; Nichol, Bob; Oravetz, Daniel; Pan, Kaike; Palanque-Delabrouille, Nathalie; Ross, Nicholas P; Simmons, Audrey; de Simoni, Fernando; Snedden, Stephanie; Yeche, Christophe
2012-01-01
The Sloan Digital Sky Survey (SDSS) surveyed 14,555 square degrees, and delivered over a trillion pixels of imaging data. We present a study of galaxy clustering using 900,000 luminous galaxies with photometric redshifts, spanning between $z=0.45$ and $z=0.65$, constructed from the SDSS using methods described in Ross et al. (2011). This data-set spans 11,000 square degrees and probes a volume of $3h^{-3} \\rm{Gpc}^3$, making it the largest volume ever used for galaxy clustering measurements. We present a novel treatment of the observational systematics and its applications to the clustering signals from the data set. In this paper, we measure the angular clustering using an optimal quadratic estimator at 4 redshift slices with an accuracy of ~15% with bin size of delta_l = 10 on scales of the Baryon Acoustic Oscillations (BAO) (at l~40-400). We derive cosmological constraints using the full-shape of the power-spectra. For a flat Lambda CDM model, when combined with Cosmic Microwave Background Wilkinson Microw...
Negative Energy Cosmology and the Cosmological Constant
Prokopec, Tomislav
2011-01-01
It is well known that string theories naturally compactify on anti-de Sitter spaces, and yet cosmological observations show no evidence of a negative cosmological constant in the early Universe's evolution. In this letter we present two simple nonlocal modifications of the standard Friedmann cosmology that can lead to observationally viable cosmologies with an initial (negative) cosmological constant. The nonlocal operators we include are toy models for the quantum cosmological backreaction. In Model I an initial quasiperiodic oscillatory epoch is followed by inflation and a late time matter era, representing a dark matter candidate. The backreaction in Model II quickly compensates the negative cosmological term such that the Ricci curvature scalar rapidly approaches zero, and the Universe ends up in a late time radiation era.
Classical and quantum Big Brake cosmology for scalar field and tachyonic models
Kamenshchik, A
2013-01-01
We study a relation between the cosmological singularities in classical and quantum theory, comparing the classical and quantum dynamics in some models possessing the Big Brake singularity - the model based on a scalar field and two models based on a tachyon-pseudo-tachyon field . It is shown that the effect of quantum avoidance is absent for the soft singularities of the Big Brake type while it is present for the Big Bang and Big Crunch singularities. Thus, there is some kind of a classical - quantum correspondence, because soft singularities are traversable in classical cosmology, while the strong Big Bang and Big Crunch singularities are not traversable.
Classical and Quantum Big Brake Cosmology for Scalar Field and Tachyonic Models
Kamenshchik, Alexander; Manti, Serena
2015-01-01
We study a relation between the cosmological singularities in classical and quantum theory, comparing the classical and quantum dynamics in some models possessing the Big Brake singularity - the model based on a scalar field and two models based on a tachyon-pseudo-tachyon field. It is shown that the effect of quantum avoidance is absent for the soft singularities of the Big Brake type while it is present for the Big Bang and Big Crunch singularities. Thus, there is some kind of a classical - quantum correspondence, because soft singularities are traversable in classical cosmology, while the strong Big Bang and Big Crunch singularities are not traversable.
a Unified Dark Energy Model from a Vanishing Speed of Sound with Emergent Cosmological Constant
Luongo, Orlando; Quevedo, Hernando
2014-11-01
The problem of the cosmic acceleration is here revisited by using the fact that the adiabatic speed of sound can be assumed to be negligible small. Within the context of general relativity, the total energy budget is recovered under the hypothesis of a vanishing speed of sound by assuming the existence of one fluid only. We find a cosmological model which reproduces the main results of the ΛCDM paradigm at late-times, showing an emergent cosmological constant, which is not at all related with the vacuum energy term. As a consequence, the model presented here behaves as a unified dark energy (DE) model.
One model of modified gravity with dynamical torsion and its cosmological consequences
Nikiforova, Vasilisa
2016-10-01
We consider a model belonging to the class of Poincarè gauge gravities. The model is free of ghosts, tachyons and gradient instabilities about Minkowski and torsionless Einstein backgrounds of sufficiently small curvature. At zero cosmological constant, the model admits a self-accelerating solution with non-Riemannian connection. We study scalar perturbations about the self-accelerating solution and find that the number of scalar modes is the same as in Minkow ski background; moreover, in the limit of small effective cosmological constant and below the UV cutoff of the low energy effective theory, the scalar sector does not have pathologies like ghosts or rapid gradient instabilities.
One model of modified gravity with dynamical torsion and its cosmological consequences
Directory of Open Access Journals (Sweden)
Nikiforova Vasilisa
2016-01-01
Full Text Available We consider a model belonging to the class of Poincarè gauge gravities. The model is free of ghosts, tachyons and gradient instabilities about Minkowski and torsionless Einstein backgrounds of sufficiently small curvature. At zero cosmological constant, the model admits a self-accelerating solution with non-Riemannian connection. We study scalar perturbations about the self-accelerating solution and find that the number of scalar modes is the same as in Minkow ski background; moreover, in the limit of small effective cosmological constant and below the UV cutoff of the low energy effective theory, the scalar sector does not have pathologies like ghosts or rapid gradient instabilities.
Classical and quantum Big Brake cosmology for scalar field and tachyonic models
Energy Technology Data Exchange (ETDEWEB)
Kamenshchik, A. Yu. [Dipartimento di Fisica e Astronomia and INFN, Via Irnerio 46, 40126 Bologna (Italy) and L.D. Landau Institute for Theoretical Physics of the Russian Academy of Sciences, Kosygin str. 2, 119334 Moscow (Russian Federation); Manti, S. [Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa (Italy)
2013-02-21
We study a relation between the cosmological singularities in classical and quantum theory, comparing the classical and quantum dynamics in some models possessing the Big Brake singularity - the model based on a scalar field and two models based on a tachyon-pseudo-tachyon field . It is shown that the effect of quantum avoidance is absent for the soft singularities of the Big Brake type while it is present for the Big Bang and Big Crunch singularities. Thus, there is some kind of a classical - quantum correspondence, because soft singularities are traversable in classical cosmology, while the strong Big Bang and Big Crunch singularities are not traversable.
Propagator with Positive Cosmological Constant in the 3D Euclidian Quantum Gravity Toy Model
Bunting, William
2014-01-01
We study the propagator on a single tetrahedron in a three dimensional toy model of quantum gravity with positive cosmological constant. The cosmological constant is included in the model via q-deformation of the spatial symmetry algebra, that is, we use the Tuarev-Viro amplitude. The expected repulsive effect of dark energy is recovered in numerical and analytic calculations of the propagator at large scales comparable to the infrared cutoff. However, due to the simplicity of the model we do not obtain the exact Newton limit of the propagator. This is a first step toward the similar calculation in the full 3+1 dimensional theory with larger numbers of simplicies.
Constraining a halo model for cosmological neutral hydrogen
Padmanabhan, Hamsa; Refregier, Alexandre
2017-02-01
We describe a combined halo model to constrain the distribution of neutral hydrogen (H I) in the post-reionization universe. We combine constraints from the various probes of H I at different redshifts: the low-redshift 21-cm emission line surveys, intensity mapping experiments at intermediate redshifts, and the Damped Lyman-Alpha (DLA) observations at higher redshifts. We use a Markov Chain Monte Carlo approach to combine the observations and place constraints on the free parameters in the model. Our best-fitting model involves a relation between neutral hydrogen mass M_{H I} and halo mass M with a non-unit slope, and an upper and a lower cutoff. We find that the model fits all the observables but leads to an underprediction of the bias parameter of DLAs at z ˜ 2.3. We also find indications of a possible tension between the H I column density distribution and the mass function of H I-selected galaxies at z ˜ 0. We provide the central values of the parameters of the best-fitting model so derived. We also provide a fitting form for the derived evolution of the concentration parameter of H I in dark matter haloes, and discuss the implications for the redshift evolution of the H I-halo mass relation.
Energy Technology Data Exchange (ETDEWEB)
Ayissi, Raoul Domingo, E-mail: raoulayissi@yahoo.fr; Noutchegueme, Norbert, E-mail: nnoutch@yahoo.fr [Department of Mathematics, Faculty of Science, University of Yaounde I, P.O. Box 812, Yaounde (Cameroon)
2015-01-15
Global solutions regular for the Einstein-Boltzmann equation on a magnetized Bianchi type-I cosmological model with the cosmological constant are investigated. We suppose that the metric is locally rotationally symmetric. The Einstein-Boltzmann equation has been already considered by some authors. But, in general Bancel and Choquet-Bruhat [Ann. Henri Poincaré XVIII(3), 263 (1973); Commun. Math. Phys. 33, 83 (1973)], they proved only the local existence, and in the case of the nonrelativistic Boltzmann equation. Mucha [Global existence of solutions of the Einstein-Boltzmann equation in the spatially homogeneous case. Evolution equation, existence, regularity and singularities (Banach Center Publications, Institute of Mathematics, Polish Academy of Science, 2000), Vol. 52] obtained a global existence result, for the relativistic Boltzmann equation coupled with the Einstein equations and using the Yosida operator, but confusing unfortunately with the nonrelativistic case. Noutchegueme and Dongho [Classical Quantum Gravity 23, 2979 (2006)] and Noutchegueme, Dongho, and Takou [Gen. Relativ. Gravitation 37, 2047 (2005)], have obtained a global solution in time, but still using the Yosida operator and considering only the uncharged case. Noutchegueme and Ayissi [Adv. Stud. Theor. Phys. 4, 855 (2010)] also proved a global existence of solutions to the Maxwell-Boltzmann system using the characteristic method. In this paper, we obtain using a method totally different from those used in the works of Noutchegueme and Dongho [Classical Quantum Gravity 23, 2979 (2006)], Noutchegueme, Dongho, and Takou [Gen. Relativ. Gravitation 37, 2047 (2005)], Noutchegueme and Ayissi [Adv. Stud. Theor. Phys. 4, 855 (2010)], and Mucha [Global existence of solutions of the Einstein-Boltzmann equation in the spatially homogeneous case. Evolution equation, existence, regularity and singularities (Banach Center Publications, Institute of Mathematics, Polish Academy of Science, 2000), Vol. 52] the
Improved cosmological model fitting of Planck data with a dark energy spike
Park, Chan-Gyung
2015-06-01
The Λ cold dark matter (Λ CDM ) model is currently known as the simplest cosmology model that best describes observations with a minimal number of parameters. Here we introduce a cosmology model that is preferred over the conventional Λ CDM one by constructing dark energy as the sum of the cosmological constant Λ and an additional fluid that is designed to have an extremely short transient spike in energy density during the radiation-matter equality era and an early scaling behavior with radiation and matter densities. The density parameter of the additional fluid is defined as a Gaussian function plus a constant in logarithmic scale-factor space. Searching for the best-fit cosmological parameters in the presence of such a dark energy spike gives a far smaller chi-square value by about 5 times the number of additional parameters introduced and narrower constraints on the matter density and Hubble constant compared with the best-fit Λ CDM model. The significant improvement in reducing the chi square mainly comes from the better fitting of the Planck temperature power spectrum around the third (ℓ≈800 ) and sixth (ℓ≈1800 ) acoustic peaks. The likelihood ratio test and the Akaike information criterion suggest that the model of a dark energy spike is strongly favored by the current cosmological observations over the conventional Λ CDM model. However, based on the Bayesian information criterion which penalizes models with more parameters, the strong evidence supporting the presence of a dark energy spike disappears. Our result emphasizes that the alternative cosmological parameter estimation with even better fitting of the same observational data is allowed in Einstein's gravity.
The anisotropic cosmological models in $f (R, T)$ gravity with $\\Lambda (T)$
Indian Academy of Sciences (India)
R CHAUBEY; A K SHUKLA
2017-04-01
The general class of anisotropic Bianchi cosmological models in $f(R, T)$ modified theories of gravity with $\\Lambda (T)$ has been considered. This paper deals with $f(R, T)$ modified theories of gravity, where the gravitational Lagrangian is given by an arbitrary function of Ricci scalar $R$ and the trace of the stress-energy tensor $T$ has been investigated for a specific choice of $f (R,T )$ = $f_{1}(R) + f_{2}(T)$. The exact solutions to the corresponding field equations are obtained in quadrature form. We have discussed three types of solutions of the average scale factor for the general class of Bianchi cosmological models by using a special law for deceleration parameter which is linear in time with a negative slope. The solutions to the Einstein field equations are obtained for three differentphysical viable cosmologies. All physical parameters are calculated and discussed in each model.
Testing anthropic reasoning for the cosmological constant with a realistic galaxy formation model
Sudoh, Takahiro; Makiya, Ryu; Nagashima, Masahiro
2016-01-01
The anthropic principle is one of the possible explanations for the cosmological constant ($\\Lambda$) problem. In previous studies, a dark halo mass threshold comparable with our Galaxy must be assumed in galaxy formation to get a reasonably large probability of finding the observed small value, $P(<$$\\Lambda_{\\rm obs})$, though stars are found in much smaller galaxies as well. Here we examine the anthropic argument by using a semi-analytic model of cosmological galaxy formation, which can reproduce many observations such as galaxy luminosity functions. We calculate the probability distribution of $\\Lambda$ by running the model code for a wide range of $\\Lambda$, while other cosmological parameters and model parameters for baryonic processes of galaxy formation are kept constant. Assuming that the prior probability distribution is flat per unit $\\Lambda$, and that the number of observers is proportional to stellar mass, we find $P(<$$\\Lambda_{\\rm obs}) = 6.7 \\%$ without introducing any galaxy mass thres...
The anisotropic cosmological models in f( R, T) gravity with Λ(T)
Chaubey, R.; Shukla, A. K.
2017-04-01
The general class of anisotropic Bianchi cosmological models in f( R, T) modified theories of gravity with Λ( T) has been considered. This paper deals with f( R, T) modified theories of gravity, where the gravitational Lagrangian is given by an arbitrary function of Ricci scalar R and the trace of the stress-energy tensor T has been investigated for a specific choice of f( R, T) = f 1( R) + f 2( T). The exact solutions to the corresponding field equations are obtained in quadrature form. We have discussed three types of solutions of the average scale factor for the general class of Bianchi cosmological models by using a special law for deceleration parameter which is linear in time with a negative slope. The solutions to the Einstein field equations are obtained for three different physical viable cosmologies. All physical parameters are calculated and discussed in each model.
Cosmological aspects of gauge mediated supersymmetry breakdown
Dalianis, Ioannis
2011-01-01
In this thesis, we study the details of some fundamental cosmological problems of the gauge mediated supersymmetry breakdown and we probe the supersymmetry breaking sector by cosmological arguments. We manifest that problems like the metastable vacuum selection and the gravitino overproduction in the reheated early universe are naturally absent in the most general class of gauge mediation models without including additional ingredients or assumptions. We also find that the gravitino can generically account for the bulk dark matter of the universe. Cosmological implications of a stringy UV-completion of the supersymmetry breaking sector have been also considered.
Beyond Standard Model Physics: At the Frontiers of Cosmology and Particle Physics
Lopez-Suarez, Alejandro O.
I begin to write this thesis at a time of great excitement in the field of cosmology and particle physics. The aim of this thesis is to study and search for beyond the standard model (BSM) physics in the cosmological and high energy particle fields. There are two main questions, which this thesis aims to address: 1) what can we learn about the inflationary epoch utilizing the pioneer gravitational wave detector Adv. LIGO?, and 2) what are the dark matter particle properties and interactions with the standard model particles?. This thesis will focus on advances in answering both questions.
Cosmological perturbations in SFT inspired non-local scalar field models
Energy Technology Data Exchange (ETDEWEB)
Koshelev, Alexey S. [Vrije Universiteit Brussel and The International Solvay Institutes, Theoretische Natuurkunde, Brussels (Belgium); Vernov, Sergey Yu. [Instituto de Ciencias del Espacio (ICE/CSIC) and Institut d' Estudis Espacials de Catalunya (IEEC), Bellaterra, Barcelona (Spain); Lomonosov Moscow State University, Theoretical High Energy Physics Division, Skobeltsyn Institute of Nuclear Physics, Moscow (Russian Federation)
2012-10-15
We study cosmological perturbations in models with a single non-local scalar field originating from the string field theory description of the rolling tachyon dynamics. We construct the equation for the energy density perturbations of the non-local scalar field and explicitly prove that for the free field it is identical to a system of local cosmological perturbation equations in a particular model with multiple (maybe infinitely many) local free scalar fields. We also show that vector and tensor perturbations are absent in this set-up. (orig.)
Unitary evolution for anisotropic quantum cosmologies: models with variable spatial curvature
Pandey, Sachin
2016-01-01
Contrary to the general belief, there has recently been quite a few examples of unitary evolution of quantum cosmological models. The present work gives more examples, namely Bianchi type VI and type II. These examples are important as they involve varying spatial curvature unlike the most talked about homogeneous but anisotropic cosmological models like Bianchi I, V and IX. We exhibit either explicit example of the unitary solutions of the Wheeler-DeWitt equation, or at least show that a self-adjoint extension is possible.
Unitary evolution for anisotropic quantum cosmologies: models with variable spatial curvature
Pandey, Sachin; Banerjee, Narayan
2016-11-01
Contrary to the general belief, there has recently been quite a few examples of unitary evolution of quantum cosmological models. The present work gives more examples, namely Bianchi type VI and type II. These examples are important as they involve varying spatial curvature unlike the most talked about homogeneous but anisotropic cosmological models like Bianchi I, V and IX. We exhibit either an explicit example of the unitary solutions of the Wheeler-DeWitt equation, or at least show that a self-adjoint extension is possible.
Standard cosmological model with non vanishing Weyl tensor
Bittencourt, E
2013-01-01
We have solved Einstein's equations of general relativity for a homogeneous and isotropic metric with constant spatial curvature and found a non vanishing Weyl tensor in the presence of an anisotropic pressure component of the energy-momentum tensor. The time evolution of the space-time is guided by the usual Friedman equations and the properties of the spatial components comprise a separated system of equations that can be independently solved. The physical features of this solution are elucidated by using the Quasi-Maxwellian equations of general relativity which directly connect the anisotropic pressure to the electric part of the Weyl tensor for the cosmological fluid.
Stable cosmological models driven by a free quantum scalar field
Energy Technology Data Exchange (ETDEWEB)
Dappiaggi, C.; Pinamonti, N. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik]|[Citta Univ., Roma (Italy). Istituto Nazionale di Alta Matematica ' ' F. Severi' ' - GNFM; Fredenhagen, K. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik
2008-01-15
In the mathematically rigorous analysis of semiclassical Einstein's equations, the renormalisation of the stress-energy tensor plays a crucial role. We address such a topic in the case of a scalar field with both arbitrary mass and coupling with gravity in the hypothesis that the underlying algebraic quantum state is of Hadamard type. Particularly, if we focus on highly symmetric solutions of the semiclassical Einstein's equations, the envisaged method displays a de Sitter type behaviour even without an a priori introduced cosmological constant. As a further novel result we shall show that these solutions turn out to be stable. (orig.)
Bianchi-I cosmological model and crossing singularities
Kamenshchik, Alexander Yu.; Pozdeeva, Ekaterina O.; Vernov, Sergey Yu.; Tronconi, Alessandro; Venturi, Giovanni
2017-04-01
We consider a rather simple method for the description of the big bang-big crunch cosmological singularity crossing. For the flat Friedmann universe this method gives the same results as more complicated methods, using Weyl symmetry or the transitions between the Jordan and Einstein frames. It is then easily generalized for the case of a Bianchi-I anisotropic universe. We also present early-time and late-time asymptotic solutions for a Bianchi-I universe, filled with a conformally coupled massless scalar field.
Lee, Namhyung
Understanding the merger rate history of galaxies is critical to understanding the formation, structure, and evolution of galaxies. Moreover, the sensitivity of the galaxy merger rate to the cosmological environment enables mutual constraints to be formulated between these two major scientific quandaries. In this dissertation, we have modeled the connection between galaxy merger rates and topologically flat cosmologies with varying multi-component energy density parameters---matter (OM), radiation (OR), cosmic strings (O S) and dark energy (OX). We performed kinematic tests deriving look back times, scale factors, deceleration parameters, proper distances, luminosity distances, angular diameter distances and comoving volume elements as a function of redshift (z). We found that models with greater O X (less OS) and more negative values of the dark energy parameter (w or alpha) provide greater values of the cosmological age H oto in fixed OM. Moreover, we found that the models with greater Hoto provide greater cosmological distances and comoving volume elements. The merger rate is often expressed as a power law of the redshift z, where the exponent m varies from 2 to 7 according to many observational and theoretical studies. We model the merger rate in terms of the number of interacting galaxies N, the dark energy parameter w (or alpha), the merger rate exponent m, and other cosmological parameters---where a flat topology is assumed. We find that m and alpha (or w) mutually constrain one another with unique dependences on particular cosmologies. Consequences of these variations on the number of galaxy mergers are plotted on Normalized Three Dimensional (N3D) plots. Forthcoming observations of the Universe's expansion history will help to further constrain alpha (or w), m, and other parameters (OX, OS and O M) relating to the structure, content, and evolution of the Universe. The inclusion of the cosmic string component, OS, in our calculation lays the groundwork for
Probing cosmology with weak lensing selected clusters II: Dark energy and f(R) gravity models
Shirasaki, Masato; Yoshida, Naoki
2015-01-01
Ongoing and future wide-field galaxy surveys can be used to locate a number of clusters of galaxies with cosmic shear measurement alone. We study constraints on cosmological models using statistics of weak lensing selected galaxy clusters. We extend our previous theoretical framework to model the statistical properties of clusters in variants of cosmological models as well as in the standard LCDM model. Weak lensing selection of clusters does not rely on the conventional assumption such as the relation between luminosity and mass and/or hydrostatic equilibrium, but a number of observational effects compromise robust identification. We use a large set of realistic mock weak-lensing catalogs as well as analytic models to perform a Fisher analysis and make forecast for constraining two competing cosmological models, wCDM model and f(R) model proposed by Hu & Sawicki, with our lensing statistics. We show that weak lensing selected clusters are excellent probe of cosmology when combined with cosmic shear power...
Dark Energy Model with Non-Minimal Coupling and Cosmological Constant Boundary
Institute of Scientific and Technical Information of China (English)
张晓菲
2011-01-01
In this paper, we study a kind of dark energy models in the framework of the non-minimal coupling. With this kind of models, dark energy could cross the cosmological constant boundary, and at early time, dark energy could have ＂tracking＂ behavior.
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.
Deformed special relativity with an invariant minimum speed and its cosmological implications
Indian Academy of Sciences (India)
Cláudio Nassif
2008-07-01
The paper aims to introduce a new symmetry principle in the space-time geometry through the elimination of the classical idea of rest and by including a universal minimum speed limit in the subatomic world. Such a limit, unattainable by particles, represents the preferred reference frame associated with a universal background field that breaks Lorentz symmetry. Thus, the structure of space-time is extended due to the presence of a vacuum energy density, which leads to a negative pressure at cosmological scales. The tiny values of the cosmological constant and the vacuum energy density shall be successfully obtained, which are in good agreement with current observational results.
A comparative study of cosmological models in alternative theory of gravity with LVDP & BVDP
Mishra, R. K.; Chand, Avtar
2017-08-01
In this communication we have presented a comparative study of Friedmann-Lemaître-Robertson-Walker (FLRW) cosmological models in alternative theory of gravity with linearly varying deceleration parameter (LVDP) and bilinearly varying deceleration parameter (BVDP) as suggested by Mishra and Chand (Astrophys. Space Sci. 361:259, 2016c). The role of viscosity in cosmology have been studied by several researchers. Under the influence of such study we have also studied bulk viscous fluid cosmological models in alternative f(R,T) theory of gravity along with comparison of results by taking LVDP and BVDP. The main conclusion of the paper is that BVDP law provides better results in comparative with Berman's constant deceleration law (CDP) and LVDP law. Also the BVDP law provides an envelope for CDP law and LVDP law.
Models of quintessence coupled to the electromagnetic field and the cosmological evolution of alpha
Copeland, E J; Pospelov, M E
2004-01-01
We study the change of the effective fine structure constant in the cosmological models of a scalar field with a non-vanishing coupling to the electromagnetic field. Combining cosmological data and terrestrial observations we place empirical constraints on the size of the possible coupling and explore a large class of models that exhibit tracking behavior. The change of the fine structure constant implied by the quasar absorption spectra together with the requirement of tracking behavior impose a lower bound of the size of this coupling. Furthermore, the transition to the quintessence regime implies a narrow window for this coupling around $10^{-5}$ in units of the inverse Planck mass. We also propose a non-minimal coupling between electromagnetism and quintessence which has the effect of leading only to changes of alpha determined from atomic physics phenomena, but leaving no observable consequences through nuclear physics effects. In doing so we are able to reconcile the claimed cosmological evidence for a ...
Hubble space telescope counts of elliptical galaxies constraints on cosmological models?
Driver, S P; Phillipps, S; Bristow, P D; Driver, Simon P; Windhorst, Rogier A; Phillipps, Steven; Bristow, Paul D
1995-01-01
The interpretation of galaxy number counts in terms of cosmological models is fraught with difficulty due to uncertainties in the overall galaxy population (mix of morphological types, luminosity functions etc.) and in the observations (loss of low surface brightness images, image blending etc.). Many of these can be overcome if we use deep high resolution imaging of a single class of high surface brightness galaxies, whose evolution is thought to be fairly well understood. This is now possible by selecting elliptical and S0 galaxies using Hubble Space Telescope images from the Medium Deep Survey and other ultradeep WFPC2 images. In the present paper, we examine whether such data can be used to discriminate between open and closed universes, or between conventional cosmological models and those dominated by a cosmological constant. We find, based on the currently available data, that unless elliptical galaxies undergo very strong merging since z \\sim 1 (and/or very large errors exist in the morphological clas...
Garcia-Salcedo, Ricardo; Quiros, Israel
2013-01-01
Here we investigate the cosmic dynamics of Friedmann-Robertson-Walker universes -- flat spatial sections -- which are driven by nonlinear electrodynamics (NLED) Lagrangians. We pay special attention to the check of the sign of the square sound speed since, whenever the latter quantity is negative, the corresponding cosmological model is classically unstable against small perturbations of the background energy density. Besides, based on causality arguments, one has to require that the mentioned small perturbations of the background should propagate at most at the local speed of light. We also look for the occurrence of curvature singularities. Our results indicate that several cosmological models which are based in known NLED Lagrangians, either are plagued by curvature singularities of the sudden and/or big rip type, or are violently unstable against small perturbations of the cosmological background -- due to negative sign of the square sound speed -- or both. In addition, causality issues associated with su...
Sanders, Robert H
2016-01-01
The advent of sensitive high-resolution observations of the cosmic microwave background radiation and their successful interpretation in terms of the standard cosmological model has led to great confidence in this model's reality. The prevailing attitude is that we now understand the Universe and need only work out the details. In this book, Sanders traces the development and successes of Lambda-CDM, and argues that this triumphalism may be premature. The model's two major components, dark energy and dark matter, have the character of the pre-twentieth-century luminiferous aether. While there is astronomical evidence for these hypothetical fluids, their enigmatic properties call into question our assumptions of the universality of locally determined physical law. Sanders explains how modified Newtonian dynamics (MOND) is a significant challenge for cold dark matter. Overall, the message is hopeful: the field of cosmology has not become frozen, and there is much fundamental work ahead for tomorrow's cosmologis...
G., Leonardo Quintanar
2015-01-01
We study the cosmological implications of the Nambu-Jona-Lasinio (NJL model) when the coupling constant is field dependent. The NJL model has a four-fermion interaction describing two different phases due to quantum interaction effects and determined by the strength of the coupling constant g. It describes massless fermions for weak coupling and a massive fermions and strong coupling, where a fermion condensate is formed. In the original NJL model the coupling constant g is indeed constant, and in this work we consider a modified version of the NJL model by introducing a dynamical field dependent coupling motivated by string theory. The effective potential as a function of the varying coupling (aimed to implement a natural phase transition) is seen to develop a negative divergence, i.e. becomes a "bottomless well" in certain limit region. Although we explain how an lower unbounded potential is not necessarily unacceptable in a cosmological context, the divergence can be removed if we consider a mass term for ...
Sánchez, Ariel G.; Scoccimarro, Román; Crocce, Martín; Grieb, Jan Niklas; Salazar-Albornoz, Salvador; Dalla Vecchia, Claudio; Lippich, Martha; Beutler, Florian; Brownstein, Joel R.; Chuang, Chia-Hsun; Eisenstein, Daniel J.; Kitaura, Francisco-Shu; Olmstead, Matthew D.; Percival, Will J.; Prada, Francisco; Rodríguez-Torres, Sergio; Ross, Ashley J.; Samushia, Lado; Seo, Hee-Jong; Tinker, Jeremy; Tojeiro, Rita; Vargas-Magaña, Mariana; Wang, Yuting; Zhao, Gong-Bo
2017-01-01
We explore the cosmological implications of anisotropic clustering measurements in configuration space of the final galaxy samples from Data Release 12 of the Sloan Digital Sky Survey III Baryon Oscillation Spectroscopic Survey. We implement a new detailed modelling of the effects of non-linearities, bias and redshift-space distortions that can be used to extract unbiased cosmological information from our measurements for scales s ≳ 20 h-1 Mpc. We combined the information from Baryon Oscillation Spectroscopic Survey (BOSS) with the latest cosmic microwave background (CMB) observations and Type Ia supernovae samples and found no significant evidence for a deviation from the Λ cold dark matter (ΛCDM) cosmological model. In particular, these data sets can constrain the dark energy equation-of-state parameter to wDE = -0.996 ± 0.042 when to be assumed time independent, the curvature of the Universe to Ωk = -0.0007 ± 0.0030 and the sum of the neutrino masses to ∑mν < 0.25 eV at 95 per cent confidence levels. We explore the constraints on the growth rate of cosmic structures assuming f(z) = Ωm(z)γ and obtain γ = 0.609 ± 0.079, in good agreement with the predictions of general relativity of γ = 0.55. We compress the information of our clustering measurements into constraints on the parameter combinations DV(z)/rd, FAP(z) and fσ8(z) at zeff = 0.38, 0.51 and 0.61 with their respective covariance matrices and find good agreement with the predictions for these parameters obtained from the best-fitting ΛCDM model to the CMB data from the Planck satellite. This paper is part of a set that analyses the final galaxy clustering data set from BOSS. The measurements and likelihoods presented here are combined with others by Alam et al. to produce the final cosmological constraints from BOSS.
Cross-correlating Planck tSZ with RCSLenS weak lensing: implications for cosmology and AGN feedback
Hojjati, Alireza; Tröster, Tilman; Harnois-Déraps, Joachim; McCarthy, Ian G.; van Waerbeke, Ludovic; Choi, Ami; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Hinshaw, Gary; Ma, Yin-Zhe; Miller, Lance; Viola, Massimo; Tanimura, Hideki
2017-10-01
We present measurements of the spatial mapping between (hot) baryons and the total matter in the Universe, via the cross-correlation between the thermal Sunyaev-Zeldovich (tSZ) map from Planck and the weak gravitational lensing maps from the Red Cluster Sequence Lensing Survey (RCSLenS). The cross-correlations are performed on the map level where all the sources (including diffuse intergalactic gas) contribute to the signal. We consider two configuration-space correlation function estimators, ξy-κ and ξ ^ {y-γ t}, and a Fourier-space estimator, C_{ℓ}^{y-κ}, in our analysis. We detect a significant correlation out to 3° of angular separation on the sky. Based on statistical noise only, we can report 13σ and 17σ detections of the cross-correlation using the configuration-space y-κ and y-γt estimators, respectively. Including a heuristic estimate of the sampling variance yields a detection significance of 7σ and 8σ, respectively. A similar level of detection is obtained from the Fourier-space estimator, C_{ℓ}^{y-κ}. As each estimator probes different dynamical ranges, their combination improves the significance of the detection. We compare our measurements with predictions from the cosmo-OverWhelmingly Large Simulations suite of cosmological hydrodynamical simulations, where different galactic feedback models are implemented. We find that a model with considerable active galactic nuclei (AGN) feedback that removes large quantities of hot gas from galaxy groups and Wilkinson Microwave Anisotropy Probe 7-yr best-fitting cosmological parameters provides the best match to the measurements. All baryonic models in the context of a Planck cosmology overpredict the observed signal. Similar cosmological conclusions are drawn when we employ a halo model with the observed 'universal' pressure profile.
Background of relic gravitons in a perfect fluid in quantum cosmological models
Energy Technology Data Exchange (ETDEWEB)
Siffert, Beatriz B. [Centro Brasileiro de Pesquisas Fisicas (ICRA/CBPF), Rio de Janeiro, RJ (Brazil). Inst. de Cosmologia, Relatividade e Astrofisica; Bessada, Dennis [Instituto Nacional de Pesquisas Espaciais (INPE), SP (Brazil). Divisao de Astrofisica
2011-07-01
Full text: We studied the evolution of tensor cosmological perturbations of quantum origin in cosmological scenarios that predict a contracting phase prior to the present expansion phase. These bouncing models constitute a very plausible alternative to the current cosmological paradigm since they may be able to solve some of the cosmological puzzles present in the standard model, such as the horizon and flatness problems, without the requirement of an initial singularity or special initial conditions. While conventional inflationary models give rise to a relic background of gravitational waves that cannot be detected with present experiments, no such prediction had been made so far using quantum bouncing models. We have obtained analytically the graviton's energy density parameter as a function of time and frequency interval - which is the physical quantity to be confronted with observations - predicted by such models with a perfect fluid equation of state. To obtain the final spectrum, we numerically solved the expression for the density parameter for the time variable. The results can then be compared with the predictions from inflationary models and with the sensitivity curves of gravitational waves current detectors, such as the Virgo and Ligo interferometers, and upcoming detectors, like the LISA space mission, to determine the possibility of detection. (author)
Cosmological models in modified gravity theories with extended nonminimal derivative couplings
Harko, Tiberiu; Lobo, Francisco S. N.; Saridakis, Emmanuel N.; Tsoukalas, Minas
2017-02-01
We construct gravitational modifications that go beyond Horndeski, namely theories with extended nonminimal derivative couplings, in which the coefficient functions depend not only on the scalar field but also on its kinetic energy. Such theories prove to be ghost-free in a cosmological background. We investigate the early-time cosmology and show that a de Sitter inflationary phase can be realized as a pure result of the novel gravitational couplings. Additionally, we study the late-time evolution, where we obtain an effective dark energy sector which arises from the scalar field and its extended couplings to gravity. We extract various cosmological observables and analyze their behavior at small redshifts for three choices of potentials, namely for the exponential, the power-law, and the Higgs potentials. We show that the Universe passes from deceleration to acceleration in the recent cosmological past, while the effective dark energy equation-of-state parameter tends to the cosmological-constant value at present. Finally, the effective dark energy can be phantomlike, although the scalar field is canonical, which is an advantage of the model.
Bianchi Type-I bulk viscous fluid string dust magnetized cosmological model in general relativity
Indian Academy of Sciences (India)
Raj Bali; Anjali
2004-09-01
Bianchi Type-I magnetized bulk viscous fluid string dust cosmological model is investigated. To get a determinate model, we have assumed the conditions and = constant where is the shear, the expansion in the model and the coefficient of bulk viscosity. The behaviour of the model in the presence and absence of magnetic field together with physical and geometrical aspects of the model are also discussed.
Cosmology and Particle Physics beyond Standard Models Ten Years of the SEENET-MTP Network
Álvarez-Gaumé, Luis; Stojkovic, Dejan
2014-01-01
This publication - "Cosmology and Particle Physics beyond Standard Models" - is dedicated to the celebration of the tenth anniversary of the Southeastern European Network in Mathematical and Theoretical Physics (SEENET-MTP). As a Theme Collection, rather than a Monograph or Proceedings, this volume presents a number of reports and overviews, a few research papers and a short note. However, some of them are excellent examples of a nowadays increasingly deep interplay between particle physics and cosmology. Contributions span a wide range of topics in cosmology, particle physics, but also gravity, including the interface of these fields. The presented work is of both theoretical and experimental/ observational nature. The contributions represent recent progress in their respective fields: inflation, dark matter, neutrino physics, supersymmetry, collider physics, string theory, quantum gravity, black hole physics and massive gravity.
Qualitative Analysis and Numerical Simulation of Equations of the Standard Cosmological Model
Ignat'ev, Yurii
2016-01-01
On the basis of qualitative theory of differential equations it is shown that dynamic system based on the system of Einstein - Klein - Gordon equations with regard to Friedman Universe has a stable center corresponding to zero values of scalar potential and its derivative at infinity. Thus, the cosmological model based on single massive classical scalar field in infinite future would give a flat Universe. The carried out numerical simulation of the dynamic system corresponding to the system of Einstein - Klein - Gordon equations showed that at great times of the evolution the invariant cosmological acceleration has a microscopic oscillating character ($T\\sim 2\\pi mt$), while macroscopic value of the cosmological acceleration varies from $+1$ at inflation stage after which if decreases fast to $-1/2$ (non-relativistic stage), and then slowly tends to $-1$ (ultrarelativistic stage).
Late time behavior of cosmological perturbations in a single brane model
Koyama, K
2004-01-01
We present solutions for the late time evolution of cosmological tensor and scalar perturbations in a single Randall-Sundrum brane world model. Assuming that the bulk is Anti-de Sitter spacetime, the solutions for cosmological perturbations are derived by summing up mode functions in Poincar\\'e coordinate. The junction conditions imposed at the moving brane are solved numerically. The recovery of 4-dimensional Einstein gravity at late times is shown by solving the 5-dimensional perturbations throughout the infinite bulk. We also comment on several possibilities to have deviations from 4-dimensional Einstein gravity.
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...
Does the diffusion DM-DE interaction model solve cosmological puzzles?
Szydlowski, Marek
2016-01-01
We study dynamics of cosmological models with diffusion effects modeling dark matter and dark energy interactions. We show the simple model with diffusion between the cosmological constant sector and dark matter, where the canonical scaling law of dark matter $(\\rho_{dm,0}a^{-3}(t))$ is modified by an additive $\\epsilon(t)=\\gamma t a^{-3}(t)$ to the form $\\rho_{dm}=\\rho_{dm,0}a^{-3}(t)+\\epsilon(t)$. We reduced this model to the autonomous dynamical system and investigate it using dynamical system methods. This system possesses a two-dimensional invariant submanifold on which the DM-DE interaction can be analyzed on the phase plane. The state variables are density parameter for matter (dark and visible) and parameter $\\delta$ characterizing the rate of growth of energy transfer between the dark sectors. A corresponding dynamical system belongs to a general class of jungle type of cosmologies represented by coupled cosmological models in a Lotka-Volterra framework. We demonstrate that the de Sitter solution is ...
Tchapnda, S B; Tchapnda, Sophonie Blaise; Noutchegueme, Norbert
2003-01-01
The Einstein-Vlasov system describes a self-gravitating, collisionless gas within the framework of general relativity. We investigate the initial value problem in a cosmological setting with surface symmetry and a non-zero cosmological constant and prove local existence and continuation criteria in both time directions. The continuation criterion says that as long as the maximum velocity remains bounded and the lapse function remains bounded then the solution can be continued. This applies to either time direction.
Classical and quantum cosmology of Born-Infeld type models
Kamenshchik, Alexander; Kwidzinski, Nick
2016-01-01
We discuss Born-Infeld type fields (tachyon fields) in classical and quantum cosmology. We first partly review and partly extend the discussion of the classical solutions and focus in particular on the occurrence of singularities. For quantization, we employ geometrodynamics. In the case of constant potential, we discuss both Wheeler-DeWitt quantization and reduced quantization. We are able to give various solutions and discuss their asymptotics. For the case of general potential, we transform the Wheeler-DeWitt equation to a form where it leads to a difference equation. Such a difference equation was previously found in the quantization of black holes. We give explicit results for the cases of constant potential and inverse square potential and point out special features possessed by solutions of the difference equation.
Classical and quantum cosmology of Born-Infeld type models
Kamenshchik, Alexander; Kiefer, Claus; Kwidzinski, Nick
2016-04-01
We discuss Born-Infeld type fields (tachyon fields) in classical and quantum cosmology. We first partly review and partly extend the discussion of the classical solutions and focus in particular on the occurrence of singularities. For quantization, we employ geometrodynamics. In the case of constant potential, we discuss both Wheeler-DeWitt quantization and reduced quantization. We are able to give various solutions and discuss their asymptotics. For the case of general potential, we transform the Wheeler-DeWitt equation to a form where it leads to a difference equation. Such a difference equation was previously found in the quantization of black holes. We give explicit results for the cases of constant potential and inverse squared potential and point out special features possessed by solutions of the difference equation.
Non-linear structure formation in the `Running FLRW' cosmological model
Bibiano, Antonio; Croton, Darren J.
2016-07-01
We present a suite of cosmological N-body simulations describing the `Running Friedmann-Lemaïtre-Robertson-Walker' (R-FLRW) cosmological model. This model is based on quantum field theory in a curved space-time and extends Lambda cold dark matter (ΛCDM) with a time-evolving vacuum density, Λ(z), and time-evolving gravitational Newton's coupling, G(z). In this paper, we review the model and introduce the necessary analytical treatment needed to adapt a reference N-body code. Our resulting simulations represent the first realization of the full growth history of structure in the R-FLRW cosmology into the non-linear regime, and our normalization choice makes them fully consistent with the latest cosmic microwave background data. The post-processing data products also allow, for the first time, an analysis of the properties of the halo and sub-halo populations. We explore the degeneracies of many statistical observables and discuss the steps needed to break them. Furthermore, we provide a quantitative description of the deviations of R-FLRW from ΛCDM, which could be readily exploited by future cosmological observations to test and further constrain the model.
Entropy - Some Cosmological Questions Answered by Model of Expansive Nondecelerative Universe
Directory of Open Access Journals (Sweden)
Miroslav Sukenik
2003-01-01
Full Text Available Abstract: The paper summarizes the background of Expansive Nondecelerative Universe model and its potential to offer answers to some open cosmological questions related to entropy. Three problems are faced in more detail, namely that of Hawkings phenomenon of black holes evaporation, maximum entropy of the Universe during its evolution, and time evolution of specific entropy.
The Weierstrass Criterion and the Lemaitre-Tolman-Bondi Models with Cosmological Constant \\lambda
Bochicchio, Ivana; Laserra, Ettore
2011-01-01
We analyze Lemaitre-Tolman-Bondi models in presence of the cosmological constant \\Lambda through the classical Weierstrass criterion. Precisely, we show that the Weierstrass approach allows us to classify the dynamics of these inhomogeneous spherically symmetric Universes taking into account their relationship with the sign of \\Lambda.
Dark energy and dust matter phases from an exact f(R)-cosmology model
Energy Technology Data Exchange (ETDEWEB)
Capozziello, S. [Dipartimento di Scienze Fisiche, Universita di Napoli ' Federico II' and INFN Sezioze di Napoli, Complesso Universitario di Monte S. Angelo, Ed. N, Via Cinthia, I-80126 Napoli (Italy)], E-mail: capozziello@na.infn.it; Martin-Moruno, P. [Colina de los Chopos, Instituto de Matematicas y Fisica Fundamental, Consejo Superior de Investigaciones Cientificas, Serrano 121, 28006 Madrid (Spain); Rubano, C. [Dipartimento di Scienze Fisiche, Universita di Napoli ' Federico II' and INFN Sezioze di Napoli, Complesso Universitario di Monte S. Angelo, Ed. N, Via Cinthia, I-80126 Napoli (Italy)
2008-06-12
We show that dust matter-dark energy combined phases can be achieved by the exact solution derived from a power law f(R) cosmological model. This example answers the query by which a dust-dominated decelerated phase, before dark-energy accelerated phase, is needed in order to form large scale structures.
An improved cosmological model fitting of Planck data with a dark energy spike
Park, Chan-Gyung
2015-01-01
The $\\Lambda$ cold dark matter ($\\Lambda\\textrm{CDM}$) model is currently known as the simplest cosmology model that best describes observations with minimal number of parameters. Here we introduce a cosmology model that is preferred over the conventional $\\Lambda\\textrm{CDM}$ one by constructing dark energy as the sum of the cosmological constant $\\Lambda$ and the additional fluid that is designed to have an extremely short transient spike in energy density during the radiation-matter equality era and the early scaling behavior with radiation and matter densities. The density parameter of the additional fluid is defined as a Gaussian function plus a constant in logarithmic scale-factor space. Searching for the best-fit cosmological parameters in the presence of such a dark energy spike gives a far smaller chi-square value by about five times the number of additional parameters introduced and narrower constraints on matter density and Hubble constant compared with the best-fit $\\Lambda\\textrm{CDM}$ model. The...
Submanifolds in space-time with unphysical extra dimensions, cosmology and warped brane world models
Smolyakov, Mikhail N
2008-01-01
The explicit coordinate transformations which show the equivalence between a four-dimensional spatially flat cosmology and an appropriate submanifold in the flat five-dimensional Minkowski space-time are presented. Analogous procedure is made for the case of five-dimensional warped brane world models. Several examples are presented.
An evaluation of cosmological models from expansion and growth of structure measurements
Zhai, Zhongxu; Blanton, Michael; Slosar, Anže; Tinker, Jeremy
2017-01-01
We compare a large suite of theoretical cosmological models to observational data from the cosmic microwave background, baryon acoustic oscillation measurements of expansion, Type Ia SNe measurements of expansion, redshift space distortion measurements of the growth of structure, and the local Hubble constant. Our theoretical models include parametrizations of dark energy as well as physical models of dark energy and modified gravity. We determine the constraints on the model parameters, inco...
A cosmological model in Weyl-Cartan spacetime; 1, Field equations and solutions
Puetzfeld, D
2001-01-01
In this first article of a series on alternative cosmological models we present an extended version of a cosmological model in Weyl-Cartan spacetime. The new model can be viewed as a generalization of a model developed earlier jointly with Tresguerres. Within this model the non-Riemannian quantities, i.e. torsion $T^{\\alpha}$ and nonmetricity $Q_{\\alpha \\beta}$, are proportional to the Weyl 1-form. The hypermomentum $\\Delta_{\\alpha \\beta}$ depends on our ansatz for the nonmetricity and vice versa. We derive the explicit form of the field equations for different cases and provide solutions for a broad class of parameters. We demonstrate that it is possible to construct models in which the non-Riemannian quantities die out with time. We show how our model fits into the more general framework of metric-affine gravity (MAG).
A cosmological model in Weyl-Cartan spacetime: I. Field equations and solutions
Puetzfeld, Dirk
2002-06-01
In this first paper of a series on alternative cosmological models we present an extended version of a cosmological model in Weyl-Cartan spacetime. The new model can be viewed as a generalization of a model developed earlier jointly with Tresguerres. Within this model the non-Riemannian quantities, i.e. torsion Tα and nonmetricity Qαβ, are proportional to the Weyl 1-form. The hypermomentum Δαβ depends on our ansatz for the nonmetricity and vice versa. We derive the explicit form of the field equations for different cases and provide solutions for a broad class of parameters. We demonstrate that it is possible to construct models in which the non-Riemannian quantities die out with time. We show how our model fits into the more general framework of metric-affine gravity (MAG).
A cosmological model in Weyl-Cartan spacetime: I. Field equations and solutions
Energy Technology Data Exchange (ETDEWEB)
Puetzfeld, Dirk [Institute for Theoretical Physics, University of Cologne, 50923 Cologne (Germany)
2002-06-21
In this first paper of a series on alternative cosmological models we present an extended version of a cosmological model in Weyl-Cartan spacetime. The new model can be viewed as a generalization of a model developed earlier jointly with Tresguerres. Within this model the non-Riemannian quantities, i.e. torsion T{sup {alpha}} and nonmetricity Q{sub {alpha}}{sub {beta}}, are proportional to the Weyl 1-form. The hypermomentum {delta}{sub {alpha}}{sub {beta}} depends on our ansatz for the nonmetricity and vice versa. We derive the explicit form of the field equations for different cases and provide solutions for a broad class of parameters. We demonstrate that it is possible to construct models in which the non-Riemannian quantities die out with time. We show how our model fits into the more general framework of metric-affine gravity (MAG)
Bamba, Kazuharu; Nojiri, Shin'ichi; Odintsov, Sergei D
2012-01-01
We review different dark energy cosmologies. In particular, we present the $\\Lambda$CDM cosmology, Little Rip and Pseudo-Rip universes, the phantom and quintessence cosmologies with Type I, II, III and IV finite-time future singularities and non-singular dark energy universes. In the first part, we explain the $\\Lambda$CDM model and well-established observational tests which constrain the current cosmic acceleration. After that, we investigate the dark fluid universe where a fluid has quite general equation of state (EoS) [including inhomogeneous or imperfect EoS]. All the above dark energy cosmologies for different fluids are explicitly realized, and their properties are also explored. It is shown that all the above dark energy universes may mimic the $\\Lambda$CDM model currently, consistent with the recent observational data. Furthermore, special attention is paid to the equivalence of different dark energy models. We consider single and multiple scalar field theories, tachyon scalar theory and holographic ...
Topological implications of the extrinsic curvature for the cosmological constant problem
Capistrano, Abraao J S
2014-01-01
The concept of smooth deformation of a Riemannian manifolds associated with the extrinsic curvature is explained and applied to FLRW cosmology. We show that such deformation can be derived from an Einstein-Hilbert-like dynamical principle producing an observable effect in the sense of Noether. The Gupta equations are used to address the problem of the cosmological constant to provide the expression of the function $b(t)$ which is a consequence of the effect of extrinsic curvature. When using such a modification, we notice on how the extrinsic curvature compensates both quantitative and qualitative difference between $ \\Lambda$ and $\\rho_{\\; vac}$ due to the topological characteristics of the extrinsic geometry. It is also shown that the coincidence problem can be alleviated in this framework.
Kiselev, V V
2012-01-01
A huge value of cosmological constant characteristic for the particle physics and the inflation of early Universe are inherently related to each other: one can construct a fine-tuned superpotential, which produces a flat potential of inflaton with a constant density of energy V=\\Lambda^4 after taking into account for leading effects due to the supergravity, so that an introduction of small quantum loop-corrections to parameters of this superpotential naturally results in the dynamical instability relaxing the primary cosmological constant by means of inflationary regime. The model phenomenologically agrees with observational data on the large scale structure of Universe at \\Lambda~10^{16} GeV.
Cosmological implications in electrodynamics due to variations of the fine structure constant
Martínez-Ledesma, J L
2002-01-01
Astronomical observations are strongly suggesting that the fine structure constant varies cosmologically. We present an analysis on the consequences that this variations might induce on the electromagnetic field as a whole. We show that under this circumstances the electrodynamics in vacuum of the universe are described by two fields, the ``standard'' Maxwell's field and a new scalar field. We provide a generalized Lorentz force which can be used to test our results experimentally.
Directory of Open Access Journals (Sweden)
Koonin Eugene V
2007-05-01
Full Text Available Abstract Background Recent developments in cosmology radically change the conception of the universe as well as the very notions of "probable" and "possible". The model of eternal inflation implies that all macroscopic histories permitted by laws of physics are repeated an infinite number of times in the infinite multiverse. In contrast to the traditional cosmological models of a single, finite universe, this worldview provides for the origin of an infinite number of complex systems by chance, even as the probability of complexity emerging in any given region of the multiverse is extremely low. This change in perspective has profound implications for the history of any phenomenon, and life on earth cannot be an exception. Hypothesis Origin of life is a chicken and egg problem: for biological evolution that is governed, primarily, by natural selection, to take off, efficient systems for replication and translation are required, but even barebones cores of these systems appear to be products of extensive selection. The currently favored (partial solution is an RNA world without proteins in which replication is catalyzed by ribozymes and which serves as the cradle for the translation system. However, the RNA world faces its own hard problems as ribozyme-catalyzed RNA replication remains a hypothesis and the selective pressures behind the origin of translation remain mysterious. Eternal inflation offers a viable alternative that is untenable in a finite universe, i.e., that a coupled system of translation and replication emerged by chance, and became the breakthrough stage from which biological evolution, centered around Darwinian selection, took off. A corollary of this hypothesis is that an RNA world, as a diverse population of replicating RNA molecules, might have never existed. In this model, the stage for Darwinian selection is set by anthropic selection of complex systems that rarely but inevitably emerge by chance in the infinite universe
On the Tidal Evolution of the Earth-Moon System: A Cosmological Model
Directory of Open Access Journals (Sweden)
Arbab A. I.
2009-01-01
Full Text Available We have presented a cosmological model for the tidal evolution of the Earth-Moon system. We have found that the expansion of the universe has immense consequences on our local systems. The model can be compared with the present observational data. The close approach problem inflicting the known tidal theory is averted in this model. We have also shown that the astronomical and geological changes of our local systems are of the order of Hubble constant.
Accelerating anisotropic cosmological model in f(R,T) theory of gravity
Santhi Kumar, R.; Satyannarayana, B.
2017-10-01
Field equations in a modified theory of gravitation proposed by Harko et al. (Phys Rev D 84:024020, 8) are obtained with the aid of a spatially homogeneous and anisotropic LRS Bianchi type-I metric. Cosmological models corresponding to false vacuum and dust universe are obtained. Some physical and kinematical properties of each of the models are discussed. These models may be physically significant for discussion at an early stage of evolution of the universe.
Bianchi type VI1 cosmological model with wet dark fluid in scale invariant theory of gravitation
Mishra, B
2014-01-01
In this paper, we have investigated Bianchi type VIh, II and III cosmological model with wet dark fluid in scale invariant theory of gravity, where the matter field is in the form of perfect fluid and with a time dependent gauge function (Dirac gauge). A non-singular model for the universe filled with disorder radiation is constructed and some physical behaviors of the model are studied for the feasible VIh (h = 1) space-time.
On the Tidal Evolution of the Earth-Moon System: A Cosmological Model
Directory of Open Access Journals (Sweden)
Arbab A. I.
2009-01-01
Full Text Available We have presented a cosmological model for the tidal evolution of the Earth-Moon system. We have found that the expansion of the universe has immense consequences on our local systems. The model can be compared with the present observational data. The close approach problem inflicting the known tidal theory is averted in this model. We have also shown that the astronomical and geological changes of our local systems are of the order of Hubble constant.
Verma, M. K.; Chandel, S.; Ram, Shri
2017-01-01
The present study deals with hypersurface-homogeneous cosmological models with anisotropic dark energy in Saez-Ballester theory of gravitation. Exact solutions of field equations are obtained by applying a special law of variation of Hubble's parameter that yields a constant negative value of the deceleration parameter. Three physically viable cosmological models of the Universe are presented for the values of parameter K occurring in the metric of the space-time. The model for K = 0 corresponds to an accelerating Universe with isotropic dark energy. The other two models for K = 1 and -1 represent accelerating Universe with anisotropic dark energy, which isotropize for large time. The physical and geometric behaviours of the models are also discussed.
Indian Academy of Sciences (India)
M K VERMA; S CHANDEL; SHRI RAM
2017-01-01
The present study deals with hypersurface-homogeneous cosmological models with anisotropic dark energy in Saez–Ballester theory of gravitation. Exact solutions of field equations are obtained by applying a special law of variation of Hubble’s parameter that yields a constant negative value of the deceleration parameter. Three physically viable cosmological models of the Universe are presented for the values of parameter $K$ occurring in the metric of the space–time. The model for $K = 0$ corresponds to an accelerating Universe with isotropic dark energy. The other two models for $K = 1$ and $−1$ represent accelerating Universe with anisotropic dark energy, which isotropize for large time. The physical and geometric behaviours of the models are also discussed.
Warps and waves in fully cosmological models of galactic discs
Gómez, Facundo A; Grand, Robert J J; Marinacci, Federico; Springel, Volker; Pakmor, Rüdiger
2016-01-01
Recent studies have revealed an oscillating asymmetry in the vertical structure of the Milky Way's disc. Here we analyze 16 high-resolution, fully cosmological simulations of the evolution of individual Milky Way-sized galaxies, carried out with the MHD code AREPO. At redshift zero, about $70\\%$ of our galactic discs show strong vertical patterns, with amplitudes that can exceed 2 kpc. Half of these are typical `integral sign' warps. The rest are oscillations similar to those observed in the Milky Way. Such structures are thus expected to be common. The associated mean vertical motions can be as large as 30 km/s. Cold disc gas typically follows the vertical patterns seen in the stars. These perturbations have a variety of causes: close encounters with satellites, distant flybys of massive objects, accretion of misaligned cold gas from halo infall or from mergers. Tidally induced vertical patterns can be identified in both young and old stellar populations, whereas those originating from cold gas accretion are...
A fully cosmological model of a Monoceros-like ring
Gómez, Facundo A; Marinacci, Federico; Slater, Colin T; Grand, Robert J J; Springel, Volker; Pakmor, Rüdiger
2015-01-01
We study the vertical structure of a stellar disk obtained from a fully cosmological high-resolution hydrodynamical simulation of the formation of a Milky Way-like galaxy. At the present day, the disk's mean vertical height shows a well-defined and strong pattern, with amplitudes as large as 3 kpc in its outer regions. This pattern is the result of a satellite - host halo - disk interaction and reproduces, qualitatively, many of the observable properties of the Monoceros Ring. In particular we find disk material at the distance of Monoceros extending far above the mid plane (30$^{\\circ}$) in both hemispheres, as well as well-defined arcs of disk material at heliocentric distances $\\gtrsim 5$ kpc. The pattern was first excited $\\approx 3$ Gyr ago as an $m=1$ mode that later winds up into a leading spiral pattern. Interestingly, the main driver behind this perturbation is a low-mass low-velocity fly-by encounter. The satellite has total mass, pericentre distance and pericentric velocity of $\\sim 5\\%$ of the hos...
Anisotropic Cosmological Model in Modified Brans--Dicke Theory
Rasouli, S M M; Sepangi, Hamid R
2011-01-01
It has been shown that four dimensional Brans-Dicke theory with effective matter field and self interacting potential can be achieved from vacuum 5D BD field equations, where we refer to as modified Brans-Dicke theory (MBDT). We investigate a generalized Bianchi type I anisotropic cosmology in 5D BD theory, and by employing obtained formalism, we derive induced-matter on any 4D hypersurface in context of the MBDT. We illustrate that if the usual spatial scale factors are functions of time while scale factor of extra dimension is constant, and scalar field depends on time and fifth coordinate, then in general, one will encounter inconsistencies in field equations. Then, we assume the scale factors and scalar field depend on time and extra coordinate as separated variables in power law forms. Hence, we find a few classes of solutions in 5D spacetime through which, we probe the one which leads to a generalized Kasner relations among Kasner parameters. The induced scalar potential is found to be in power law or i...
Solar gravitation and cosmology
Energy Technology Data Exchange (ETDEWEB)
Ferrari, J.A. (Departamento de Fisica, Facultad de Humanidades y Ciencias, Montevideo (Uruguay))
1984-08-11
The objective of this paper is to discuss some implications of a scalar of gravitation developed in a previous paper. At the beginning we shall show that, on the basis of a scalar theory of gravitation, it is possible to predict a gravitational light drag. The remainder of this paper is devoted to cosmology. We shall prove that Hubble's red shift, the existence of an age and an ''effective radius'' of the Universe can be deduced from a model of the universe that is Euclidean, infinite and nonexpanding. Finally, we discuss briefly Olbers' paradox and the thermal evolution of the universe.
Constraining entropic cosmology
Energy Technology Data Exchange (ETDEWEB)
Koivisto, Tomi S. [Institute for Theoretical Physics and the Spinoza Institute, Utrecht University, Leuvenlaan 4, Postbus 80.195, 3508 TD Utrecht (Netherlands); Mota, David F. [Institute of Theoretical Astrophysics, University of Oslo, 0315 Oslo (Norway); Zumalacárregui, Miguel, E-mail: t.s.koivisto@uu.nl, E-mail: d.f.mota@astro.uio.no, E-mail: miguelzuma@icc.ub.edu [Institute of Cosmos Sciences (ICC-IEEC), University of Barcelona, Marti i Franques 1, E-08028 Barcelona (Spain)
2011-02-01
It has been recently proposed that the interpretation of gravity as an emergent, entropic phenomenon might have nontrivial implications to cosmology. Here several such approaches are investigated and the underlying assumptions that must be made in order to constrain them by the BBN, SneIa, BAO and CMB data are clarified. Present models of inflation or dark energy are ruled out by the data. Constraints are derived on phenomenological parameterizations of modified Friedmann equations and some features of entropic scenarios regarding the growth of perturbations, the no-go theorem for entropic inflation and the possible violation of the Bekenstein bound for the entropy of the Universe are discussed and clarified.
Cosmological analysis of scalar field models in f(R, T) gravity
Energy Technology Data Exchange (ETDEWEB)
Sharif, M.; Nawazish, Iqra [University of the Punjab, Department of Mathematics, Lahore (Pakistan)
2017-03-15
This paper determines the existence of Noether symmetry in non-minimally coupled f(R, T) gravity admitting minimal coupling with scalar field models. We consider a generalized spacetime which corresponds to different anisotropic and homogeneous universe models. We formulate symmetry generators along with conserved quantities through Noether symmetry technique for direct and indirect curvature-matter coupling. For dust and perfect fluids, we evaluate exact solutions and construct their cosmological analysis through some cosmological parameters. We conclude that decelerated expansion is obtained for the quintessence model with a dust distribution, while a perfect fluid with dominating potential energy over kinetic energy leads to the current cosmic expansion for both phantom as well as quintessence models. (orig.)
Pasqua, Antonio; Chattopadhyay, Surajit; Assaf, Khudhair A.; Salako, Ines G.
2016-06-01
In this paper, we study the properties of the Holographic Dark Energy (HDE) model in the context of Kaluza-Klein (KK) cosmology with infrared cut-off given by the recently proposed by Granda-Oliveros cut-off, which contains a term proportional to the time derivative of the Hubble parameter and one proportional to the Hubble parameter squared. Moreover, this cut-off is characterized by two free parameters which are the proportional constants of the two terms of the cut-off. We derive the expression of the Equation of State (EoS) parameter ωD and of the deceleration parameter q for both non-interacting and interacting Dark Sectors and in the limiting case of a flat Dark Dominated Universe. Moreover, we study the squared speed of the sound vs2 and the statefinder diagnostic \\{r,s\\} in order to understand the cosmological properties of the model considered. We also develop a correspondence between the model considered and three scalar field models: the tachyon, the k-essence and the quintessence ones.
Does the diffusion dark matter-dark energy interaction model solve cosmological puzzles?
Szydłowski, Marek; Stachowski, Aleksander
2016-08-01
We study dynamics of cosmological models with diffusion effects modeling dark matter and dark energy interactions. We show the simple model with diffusion between the cosmological constant sector and dark matter, where the canonical scaling law of dark matter (ρd m ,0a-3(t )) is modified by an additive ɛ (t )=γ t a-3(t ) to the form ρd m=ρd m ,0a-3(t )+ɛ (t ). We reduced this model to the autonomous dynamical system and investigate it using dynamical system methods. This system possesses a two-dimensional invariant submanifold on which the dark matter-dark energy (DM-DE) interaction can be analyzed on the phase plane. The state variables are density parameter for matter (dark and visible) and parameter δ characterizing the rate of growth of energy transfer between the dark sectors. A corresponding dynamical system belongs to a general class of jungle type of cosmologies represented by coupled cosmological models in a Lotka-Volterra framework. We demonstrate that the de Sitter solution is a global attractor for all trajectories in the phase space and there are two repellers: the Einstein-de Sitter universe and the de Sitter universe state dominating by the diffusion effects. We distinguish in the phase space trajectories, which become in good agreement with the data. They should intersect a rectangle with sides of Ωm ,0∈[0.2724 ,0.3624 ] , δ ∈[0.0000 ,0.0364 ] at the 95% CL. Our model could solve some of the puzzles of the Λ CDM model, such as the coincidence and fine-tuning problems. In the context of the coincidence problem, our model can explain the present ratio of ρm to ρd e, which is equal 0.457 6-0.0831+0.1109 at a 2 σ confidence level.
Viability of Arctan Model of f(R) Gravity for Late-time Cosmology
Dutta, Koushik; Patel, Avani
2016-01-01
$f(R)$ modifications of Einstein's gravity is an interesting possibility to explain the late time acceleration of the Universe. In this work we explore the cosmological viability of one such $f(R)$ modification proposed in (Kruglov:2013). We show that the model violates fifth-force constraints. The model is also plagued with the issue of curvature singularity in a spherically collapsing object, where the effective scalar field reaches to the point of diverging scalar curvature.
Cosmological constraints on some supergravity-induced low-energy electroweak models
Energy Technology Data Exchange (ETDEWEB)
Girardi, G.; Salati, P.
1986-02-24
We present constraints on the parameters for models with gravity-induced supersymmetry breaking, obtained from cosmology. This is done by studying the evolution of the density of the lightest supersymmetric particle appearing in the mass spectrum. Our analysis, specifically done for models proposed by Cremmer, Fayet and Girardello, gives severe constraints on the mass of the neutral higgsinos, whereas those on the zino mass are very sensitive to the assumed value of the critical energy density of the Universe. (orig.).
Constraining a bulk viscous matter-dominated cosmological model using SNe Ia, CMB and LSS
Avelino, Arturo; Guzmán, F S
2008-01-01
We present and constrain a cosmological model which component is a pressureless fluid with bulk viscosity as an explanation for the present accelerated expansion of the universe. We study the particular model of a constant bulk viscosity coefficient \\zeta_m. The possible values of \\zeta_m are constrained using the cosmological tests of SNe Ia Gold 2006 sample, the CMB shift parameter R from the three-year WMAP observations, the Baryon Acoustic Oscillation (BAO) peak A from the Sloan Digital Sky Survey (SDSS) and the Second Law of Thermodynamics (SLT). It was found that this model is in agreement with the SLT using only the SNe Ia test. However when the model is submitted to the three cosmological tests together (SNe+CMB+BAO) the results are: 1.- the model violates the SLT, 2.- predicts a value of H_0 \\approx 53 km sec^{-1} Mpc^{-1} for the Hubble constant, and 3.- we obtain a bad fit to data with a \\chi^2_{min} \\approx 400 (\\chi^2_{d.o.f.} \\approx 2.2). These results indicate that this model is ruled out by t...
A MAGNIFIED GLANCE INTO THE DARK SECTOR: PROBING COSMOLOGICAL MODELS WITH STRONG LENSING IN A1689
Energy Technology Data Exchange (ETDEWEB)
Magaña, Juan; Motta, V.; Cárdenas, Victor H.; Verdugo, T. [Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Avda. Gran Bretaña 1111, Valparaíso (Chile); Jullo, Eric, E-mail: juan.magana@uv.cl, E-mail: veronica.motta@uv.cl, E-mail: victor.cardenas@uv.cl, E-mail: tomasverdugo@gmail.com, E-mail: eric.jullo@lam.fr [Aix Marseille Universite, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France)
2015-11-01
In this paper we constrain four alternative models to the late cosmic acceleration in the universe: Chevallier–Polarski–Linder (CPL), interacting dark energy (IDE), Ricci holographic dark energy (HDE), and modified polytropic Cardassian (MPC). Strong lensing (SL) images of background galaxies produced by the galaxy cluster Abell 1689 are used to test these models. To perform this analysis we modify the LENSTOOL lens modeling code. The value added by this probe is compared with other complementary probes: Type Ia supernovae (SN Ia), baryon acoustic oscillations (BAO), and cosmic microwave background (CMB). We found that the CPL constraints obtained for the SL data are consistent with those estimated using the other probes. The IDE constraints are consistent with the complementary bounds only if large errors in the SL measurements are considered. The Ricci HDE and MPC constraints are weak, but they are similar to the BAO, SN Ia, and CMB estimations. We also compute the figure of merit as a tool to quantify the goodness of fit of the data. Our results suggest that the SL method provides statistically significant constraints on the CPL parameters but is weak for those of the other models. Finally, we show that the use of the SL measurements in galaxy clusters is a promising and powerful technique to constrain cosmological models. The advantage of this method is that cosmological parameters are estimated by modeling the SL features for each underlying cosmology. These estimations could be further improved by SL constraints coming from other galaxy clusters.
Tremmel, Michael; Governato, Fabio; Volonteri, Marta; Quinn, Tom; Pontzen, Andrew; Anderson, Lauren
2016-01-01
We present a novel implementation of supermassive black hole (SMBH) formation, dynamics, and accretion in the massively parallel tree+SPH code, ChaNGa. This approach improves the modeling of SMBHs in fully cosmological simulations, allowing for a more detailed analysis of SMBH-galaxy co-evolution throughout cosmic time. Our scheme includes novel, physically motivated models for SMBH formation, dynamics and sinking timescales within galaxies, and SMBH accretion of rotationally supported gas. The sub-grid parameters that regulate star formation (SF) and feedback from SMBHs and SNe are optimized against a comprehensive set of z = 0 galaxy scaling relations using a novel, multi-dimensional parameter search. We have incorporated our new SMBH implementation and parameter optimization onto a new set of high resolution, large-scale cosmological simulations called Romulus. We present initial results from our flagship simulation, Romulus25, showing that our SMBH model results in SF efficiency, SMBH masses, and global c...
Cosmological Parameter Estimation from SN Ia data: a Model-Independent Approach
Benitez-Herrera, S; Maturi, M; Hillebrandt, W; Bartelmann, M; Röpke, F; .,
2013-01-01
We perform a model independent reconstruction of the cosmic expansion rate based on type Ia supernova data. Using the Union 2.1 data set, we show that the Hubble parameter behaviour allowed by the data without making any hypothesis about cosmological model or underlying gravity theory is consistent with a flat LCDM universe having H_0 = 70.43 +- 0.33 and Omega_m=0.297 +- 0.020, weakly dependent on the choice of initial scatter matrix. This is in closer agreement with the recently released Planck results (H_0 = 67.3 +- 1.2, Omega_m = 0.314 +- 0.020) than other standard analyses based on type Ia supernova data. We argue this might be an indication that, in order to tackle subtle deviations from the standard cosmological model present in type Ia supernova data, it is mandatory to go beyond parametrized approaches.
The time evolution of cosmological redshift in non-standard dark energy models
Balbi, A
2007-01-01
The variation of the expansion rate of the universe with time produces an evolution in the cosmological redshift of distant sources (for example quasars), that might be directly observed (over a decade or so) by future ultra stable, high-resolution spectrographs (such as CODEX) coupled to extremely large telescopes (such as ESO's ELT). This would open a new window to explore the physical mechanism responsible for the current acceleration of the universe. We investigate the evolution of cosmological redshift from a variety of non-standard dark energy models, and compare it with simulated data based on realistic assumptions. We perform a Fisher matrix analysis, in order to estimate the expected constraints on the parameters of the models. We find that there are interesting prospects for constraining the parameters of non-standard dark energy models and for discriminating among competing candidates.
How robust are inflation model and dark matter constraints from cosmological data?
DEFF Research Database (Denmark)
Hamann, Jan; Hannestad, Steen; Sloth, Martin Snoager;
2006-01-01
High-precision data from observation of the cosmic microwave background and the large scale structure of the universe provide very tight constraints on the effective parameters that describe cosmological inflation. Indeed, within a constrained class of LambdaCDM models, the simple lambda phi^4...... chaotic inflation model already appears to be ruled out by cosmological data. In this paper, we compute constraints on inflationary parameters within a more general framework that includes other physically motivated parameters such as a nonzero neutrino mass. We find that a strong degeneracy between...... the tensor-to-scalar ratio r and the neutrino mass prevents lambda phi^4 from being excluded by present data. Reversing the argument, if lambda phi^4 is the correct model of inflation, it predicts a sum of neutrino masses at 0.3-0.5 eV, a range compatible with present experimental limits and within the reach...
Bianchi Type-Ⅴ Bulk Viscous Barotropic Fluid Cosmological Model with Variable G and A
Institute of Scientific and Technical Information of China (English)
Raj Bali; Seema Tinker
2008-01-01
@@ We investigate the Bianehi type-Ⅴ bulk viscous barotropic fluid cosmological model with variable gravitational constant G and the cosmological constant A, assuming the condition on metric potential as A/A=B/B=C/C=m/ln, where A, B, and C are functions of time t, while m and n are constants. To obtain the deterministic model, we also assume the relations P= p-3ηH, p =γρ, η = ηoρs, where p is the isotropic pressure, η the bulk viscosity, 0 ≤γ≤1, H the Hubble constant, ηo and s are constants. Various physical aspects of the model are discussed. The case of n = 1 is also discussed to compare the results with the actual universe.
Models for the Brane-Bulk Interaction: Toward Understanding Braneworld Cosmological Perturbation
Binétruy, Pierre; Carvalho, Carla
2004-01-01
Using some simple toy models, we explore the nature of the brane-bulk interaction for cosmological models with a large extra dimension. We are in particular interested in understanding the role of the bulk gravitons, which from the point of view of an observer on the brane will appear to generate dissipation and nonlocality, effects which cannot be incorporated into an effective (3+1)-dimensional Lagrangian field theoretic description. We explicitly work out the dynamics of several discrete systems consisting of a finite number of degrees of freedom on the boundary coupled to a (1+1)-dimensional field theory subject to a variety of wave equations. Systems both with and without time translation invariance are considered and moving boundaries are discussed as well. The models considered contain all the qualitative feature of quantized linearized cosmological perturbations for a Randall-Sundrum universe having an arbitrary expansion history, with the sole exception of gravitational gauge invariance, which will b...
An Emergent Universe with Dark Sector Fields in a Chiral Cosmological Model
Beesham, A; Maharaj, S D; Kubasov, A S
2013-01-01
We consider the emergent universe scenario supported by a chiral cosmological model with two interacting dark sector fields: phantom and canonical. We investigate the general properties of the evolution of the kinetic and potential energies as well as the development of the equation of state with time. We present three models based on asymptotic solutions and investigate the phantom part of the potential and chiral metric components. The exact solution corresponding to a global emergent universe scenario, starting from the infinite past and evolving to the infinite future, has been obtained for the first time for a chiral cosmological model. The behavior of the chiral metric components responsible for the kinetic interaction between the phantom and canonical scalar fields has been analyzed as well.
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.
Detection of spatial correlations of fundamental plane residuals, and cosmological implications
Joachimi, Benjamin; Mandelbaum, Rachel
2015-01-01
The fundamental plane (FP) is a widely used tool to investigate the properties of early-type galaxies, and the tight relation between its parameters has spawned several cosmological applications, including its use as a distance indicator for peculiar velocity surveys and as a means to suppress intrinsic noise in cosmic size magnification measurements. Systematic trends with the large-scale structure across the FP could cause serious biases for these cosmological probes, but may also yield new insights into the early-type population. Here we report the first detection of spatial correlations among offsets in galaxy size from an FP that explicitly accounts for redshift trends, using a sample of about $95,000$ elliptical galaxies from the Sloan Digital Sky Survey. We show that these offsets correlate with the density field out to at least $10h^{-1}$Mpc at $4\\sigma$ significance in a way that cannot be explained by systematic errors in galaxy size estimates. We propose a physical explanation for the correlations ...
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.
Correlation of CMB with large-scale structure: I. ISW Tomography and Cosmological Implications
Ho, Shirley; Padmanabhan, Nikhil; Seljak, Uros; Bahcall, Neta
2008-01-01
We cross-correlate large scale structure (LSS) observations from a number of surveys with CMB anisotropies from WMAP to investigate the Integrated Sachs-Wolfe (ISW) effect as a function of redshift, covering z~0.1-2.5. Our main goal is to go beyond reporting detections towards developing a reliable likelihood analysis that allows one to determine cosmological constraints from ISW observations. With this in mind we spend a considerable amount of effort in determining the redshift-dependent bias and redshift distribution b(z)*dN/dz of these samples by matching with spectroscopic observations where available, and analyzing auto-power spectra and cross-power spectra between the samples. The data sets we use are 2-Micron All Sky Survey (2MASS) samples, Sloan Digital Sky Survey (SDSS) photometric Luminous Red Galaxies, SDSS photometric quasars and NRAO VLA Sky Survey (NVSS) radio sources. We make a joint analysis of all samples constructing a full covariance matrix, which we subsequently use for cosmological parame...
Dark Energy, Particle Physics and Cosmology
Turner, Michael S.
2012-05-01
Dark energy and cosmic acceleration is one of the three pillars of the current cosmological paradigm. Moreover, both raise fundamental issues in cosmology and particle physics. In particle physics, the dark energy problem is intimately related to the perplexing issue of why the quantum energy of the vacuum is so small. In cosmology, the nature of the dark energy is crucial to understanding the destiny of the Universe. I will discuss the status of current models for dark energy -- including vacuum energy and rolling scalar fields -- their implications for cosmology and for particle physics and how they can be tested by WFIRST. I will also address the status of the possibility that cosmic acceleration is explained by modifying or replacing general relativity.
Indian Academy of Sciences (India)
Chandel S; Ram Shri
2016-03-01
The paper deals with the study of particle creation and bulk viscosity in the evolution of spatially homogeneous and anisotropic Bianchi type-V cosmological models in the framework of Saez–Ballester theory of gravitation. Particle creation and bulk viscosity are considered as separate irreversible processes. The energy–momentum tensor is modified to accommodate the viscous pressure and creation pressure which is associated with the creation of matter out of gravitational field. A special law of variation of Hubble parameter is applied to obtain exact solutions of field equations in two types of cosmologies, one with power-law expansion and the other with exponential expansion. Cosmological model with power-law expansion has a Big-Bang singularity at time $t = 0$, whereas the model with exponential expansion has no finite singularity. We study bulk viscosity and particle creation in each model in four different cases. The bulk viscosity coefficient is obtained for full causal, Eckart’s and truncated theories. All physical parameters are calculated and thoroughly discussed in both models.
Peel, Austin; Troxel, M A
2012-01-01
We use the Szekeres inhomogeneous cosmological models to study the growth of large-scale structure in the universe including nonzero spatial curvature and a cosmological constant. In particular, we use the Goode and Wainwright formulation, as in this form the models can be considered to represent exact nonlinear perturbations of an averaged background. We identify a density contrast in both classes I and II of the models, for which we derive growth evolution equations. By including Lambda, the time evolution of the density contrast as well as kinematic quantities can be tracked through the matter- and Lambda-dominated cosmic eras up to the present and into the future. In various models of class I and class II, the growth rate is found to be stronger than that of the LCDM cosmology, and it is suppressed at later times due to the presence of Lambda. We find that there are Szekeres models able to provide a growth history similar to that of LCDM while requiring less matter content and nonzero curvature, which spe...
Cosmological dynamics of magnetic Bianchi I in viable f(R) models of gravity
Liu, Xuyang; Channuie, Phongpichit; Samart, Daris
2017-09-01
Standard dynamical system analysis of Einstein-Maxwell equation in f(R) theories is considered in this work. We investigate cosmological dynamics of a uniform magnetic field in the Orthogonal Spatially Homogeneous (OSH) Bianchi I universe with viable f(R) models of gravity. In this work, the f(R) = R - αRn and f(R) =(Rb - Λ) c models are examined by using our dynamical system analysis. Our results show that both of two f(R) models have a viable cosmological consequence identical to the analysis present in Amendola and Tsujikawa (2008) for the FLRW background. Contrary to Amendola and Tsujikawa (2008), we discover in our models that there is an additional anisotropic and non-zero cosmological magnetic fields fixed point emerging before the present of the standard matter epoch. This means that the universe has initially isotropic stage with the intermediated epoch as the anisotropic background and it ends up with the isotropic late-time acceleration. The primordial magnetic fields play a crucial role of the shear evolutions obtained from these two models which have the same scaling of the cosmic time as σ ∼t-1/3, instead of σ ∼t-1 for the absence of the primordial magnetic cases.
String cosmology and the dimension of spacetime
Cleaver, G B; Gerald B Cleaver; Philip J Rosenthal
1994-01-01
The implications of string theory for understanding the dimension of uncompactified spacetime are investigated. Using recent ideas in string cosmology, a new model is proposed to explain why three spatial dimensions grew large. Unlike the original work of Brandenberger and Vafa, this paradigm uses the theory of random walks. A computer model is developed to test the implications of this new approach. It is found that a four-dimensional spacetime can be explained by the proper choice of initial conditions.
String Cosmology and the Dimension of Spacetime
Cleaver, Gerald B.; Rosenthal, Philip J.
1994-01-01
The implications of string theory for understanding the dimension of uncompactified spacetime are investigated. Using recent ideas in string cosmology, a new model is proposed to explain why three spatial dimensions grew large. Unlike the original work of Brandenberger and Vafa, this paradigm uses the theory of random walks. A computer model is developed to test the implications of this new approach. It is found that a four-dimensional spacetime can be explained by the proper choice of initia...
Mead, Alexander; Heymans, Catherine; Joudaki, Shahab; Heavens, Alan
2015-01-01
We present an optimised variant of the halo model, designed to produce accurate matter power spectra well into the non-linear regime for a wide range of cosmological models. To do this, we introduce physically-motivated free parameters into the halo-model formalism and fit these to data from high-resolution N-body simulations. For a variety of $\\Lambda$CDM and $w$CDM models the halo-model power is accurate to $\\simeq 5$ per cent for $k\\leq 10h\\,\\mathrm{Mpc}^{-1}$ and $z\\leq 2$. We compare our results with recent revisions of the popular HALOFIT model and show that our predictions are more accurate. An advantage of our new halo model is that it can be adapted to account for the effects of baryonic feedback on the power spectrum. We demonstrate this by fitting the halo model to power spectra from the OWLS hydrodynamical simulation suite via parameters that govern halo internal structure. We are able to fit all feedback models investigated at the 5 per cent level using only two free parameters, and we place limi...
Plionis, M.
2004-07-01
The recent scientific efforts in Astrophysics & Cosmology have brought a revolution to our understanding of the Cosmos. Amazing results is the outcome of amazing experiments! The huge scientific, technological & financial effort that has gone into building the 10-m class telescopes as well as many space and balloon observatories, essential to observe the multitude of cosmic phenomena in their manifestations at different wavelengths, from gamma-rays to the millimetre and the radio, has given and is still giving its fruits of knowledge. These recent scientific achievements in Observational and Theoretical Cosmology were presented in the "Multiwavelength Cosmology" conference that took place on beautiful Mykonos island in the Aegean between 17 and 20 June 2003. More than 180 Cosmologists from all over the world gathered for a four-day intense meeting in which recent results from large ground based surveys (AAT/2-df, SLOAN) and space missions (WMAP, Chandra, XMM, ISO, HST) were presented and debated, providing a huge impetus to our knowledge of the Cosmos. The future of the subject (experiments, and directions of research) was also discussed. The conference was devoted mostly on the constraints on Cosmological models and galaxy formation theories that arise from the study of the high redshift Universe, from clusters of galaxies, and their evolution, from the cosmic microwave background, the large-scale structure and star-formation history. Link: http://www.wkap.nl/prod/b/1-4020-1971-8
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...
Tipler, Frank J.
1996-10-01
It is generally believed that it is not possible to rigorously analyze a homogeneous and isotropic cosmological model in Newtonian mechanics. I show on the contrary that if Newtonian gravity theory is rewritten in geometrical language in the manner outlined in 1923-1924 by Élie Cartan [Ann. Ecole Norm. Sup. 40, 325-412 (1923); 41, 1-25 (1924)], then Newtonian cosmology is as rigorous as Friedmann cosmology. In particular, I show that the equation of geodesic deviation in Newtonian cosmology is exactly the same as equation of geodesic deviation in the Friedmann universe, and that this equation can be integrated to yield a constraint equation formally identical to the Friedmann equation. However, Newtonian cosmology is more general than Friedmann cosmology: Ever-expanding and recollapsing universes are allowed in any noncompact homogeneous and isotropic spatial topology. I shall give a brief history of attempts to do cosmology in the framework of Newtonian mechanics.
Off The Beaten Path: Modeling the Dynamics of Supermassive Black Holes in Cosmological Simulations
Tremmel, Michael J.; Governato, Fabio; Volonteri, Marta; Quinn, Thomas R.
2015-01-01
Cosmological simulations are an essential tool to understand the co-evolution of supermassive black holes (SMBHs) and their host galaxies. However, the limited resolution of these simulations presents unique challenges to successfully modeling black hole dynamics. We present a novel, physically motivated method for improving the dynamics of black holes in cosmological simulations, by accounting for the unresolved dynamical friction that SMBHs feel from stars and dark matter. We show how this approach, which naturally scales with resolution, is a major step forward compared to more commonly used 'advection' models that often assume SMBHs sink very rapidly toward the center of their host galaxies. Here, we demonstrate that our method is able to prevent numerical heating of SMBHs while allowing for realistic dynamics.Our implementation will allow us to more realistically model SMBH dynamics, accretion, and mergers in cosmological simulations, giving us the ability to better understand how SMBHs grow with their host galaxies. This also provides an opportunity for more detailed studies of SMBHs in dwarf galaxies, which can give crucial insight into constraining black hole seed formation models.
Halo Models of Large Scale Structure and Reliability of Cosmological N-Body Simulations
Gaite, Jose
2013-01-01
Halo models of the large scale structure of the Universe are critically examined, focusing on the definition of halos as smooth distributions of cold dark matter. This definition is essentially based on the results of cosmological N-body simulations. By a careful analysis of the standard assumptions of halo models and N-body simulations and by taking into account previous studies of self-similarity of the cosmic web structure, we conclude that N-body cosmological simulations are not fully reliable in the range of scales where halos appear. Therefore, to have a consistent definition of halos, it is necessary either to define them as entities of arbitrary size with a grainy rather than smooth structure or to define their size in terms of small-scale baryonic physics.
Halo Models of Large Scale Structure and Reliability of Cosmological N-Body Simulations
Directory of Open Access Journals (Sweden)
José Gaite
2013-05-01
Full Text Available Halo models of the large scale structure of the Universe are critically examined, focusing on the definition of halos as smooth distributions of cold dark matter. This definition is essentially based on the results of cosmological N-body simulations. By a careful analysis of the standard assumptions of halo models and N-body simulations and by taking into account previous studies of self-similarity of the cosmic web structure, we conclude that N-body cosmological simulations are not fully reliable in the range of scales where halos appear. Therefore, to have a consistent definition of halos is necessary either to define them as entities of arbitrary size with a grainy rather than smooth structure or to define their size in terms of small-scale baryonic physics.
Future evolution in a backreaction model and the analogous scalar field cosmology
Ali, Amna
2016-01-01
We investigate the future evolution of the universe using the Buchert framework for averaged backreaction in the context of a two-domain partition of the universe. We show that this approach allows for the possibility of the global acceleration vanishing at a finite future time, provided that none of the subdomains accelerate individually. The model at large scales is analogously described in terms of a homogeneous scalar field emerging with a potential that is fixed and free from phenomenological parametrization. The dynamics of this scalar field is explored in the analogous FLRW cosmology. We use observational data from Type Ia Supernovae, Baryon Acoustic Oscillations, and Cosmic Microwave Background to constrain the parameters of the model for a viable cosmology, providing the corresponding likelihood contours.
Institute of Scientific and Technical Information of China (English)
LI Jie-Chao; XU Li-Xin; L(U) Jian-Bo; CHANG Sao-Rong; LIU Hong-Ya
2008-01-01
We study the constraint on deceleration parameter q from the recent SNeIa Gold dataset and observational Hubble data by using a model-independent deceleration parameter q(z)=1/2-a/(1+z)b under the five-dimensional bounce cosmological model.For the cases of SNeIa Gold dataset,Hubble data,and their combination,the present results cosmological.For the cases of SNeIa Cold dataset,and their combintion,the present results show that the constraints on transition redshift zT are 0.35+0.14-0.07,0.68+1.47-0.58,and 0.55+0.18-0.09 with lo errors,respectively.
On the Dynamics of the Massless Spin-1 Particles in the Rotating Cosmological Models
Salti, M; Havare, A; Korunur, M; Salti, Mustafa; Aydogdu, Oktay; Havare, Ali; Korunur, Murat
2005-01-01
In the present article, we have considered massless Duffin-Kemmer-Petiau equation for the general rotating space-times, and obtain its second order form in this cosmological model. Considering this second order differential equation for some well-known cosmological model which are included by the our general line-element, we obtain exact solution of the massless Duffin-Kemmer-Petiau equation. On the other hand, by using spinor form of the Maxwell equations the propagation problem is reduced to the solution of the second order differential equation of complex combination of the electric and magnetic fields. For these two different approach we obtain the spinors in terms of field strength tensor.
Interacting dark energy models in Cosmology and large-scale structure observational tests
Marcondes, Rafael J F
2016-01-01
Modern Cosmology offers us a great understanding of the universe with striking precision, made possible by the modern technologies of the newest generations of telescopes. The standard cosmological model, however, is not absent of theoretical problems and open questions. One possibility that has been put forward is the existence of a coupling between dark sectors. The idea of an interaction between the dark components could help physicists understand why we live in an epoch of the universe where dark matter and dark energy are comparable in terms of energy density, which can be regarded as a coincidence given that their time evolutions are completely different. We introduce the interaction phenomenologically and proceed to test models of interaction with observations of redshift-space distortions. In a flat universe composed only of those two fluids, we consider separately two forms of interaction, through terms proportional to the densities of both dark energy and dark matter. An analytic expression for the ...
Testing anthropic reasoning for the cosmological constant with a realistic galaxy formation model
Sudoh, Takahiro; Totani, Tomonori; Makiya, Ryu; Nagashima, Masahiro
2017-01-01
The anthropic principle is one of the possible explanations for the cosmological constant (Λ) problem. In previous studies, a dark halo mass threshold comparable with our Galaxy must be assumed in galaxy formation to get a reasonably large probability of finding the observed small value, P(running the model code for a wide range of Λ, while other cosmological parameters and model parameters for baryonic processes of galaxy formation are kept constant. Assuming that the prior probability distribution is flat per unit Λ, and that the number of observers is proportional to stellar mass, we find P(extremely small, we conclude that the anthropic argument is a viable explanation, if the value of Λ observed in our Universe is determined by a probability distribution.
(Non?)-Equivalence of Einstein and Jordan frames in quantized cosmological models
Pandey, Sachin; Banerjee, Narayan
2016-01-01
The present work sheds light on the nature of mathematical equivalence of Jordan frame and its conformally transformed version, the Einstein frame, as far as Brans-Dicke theory is concerned. It is shown that question of equivalence surviving a quantization of cosmological models in the theory is intricately related to whether the canonical structure breaks down while going from one frame to the other. It is found that that the consistent operator ordering to make two frames equivalent requires a non-canonical transformation that mixes gravity sector with scalar sector to undo the non minimal coupling, present in Jordan frame. The question of equivalence thus depends on the details of quantization prescriptions, i.e. whether we are allowed to make any such non-canonical transformation at classical level before quantizing the theory. We work with the Wheeler-deWitt quantization scheme and take up quite a few anisotropic cosmological models as examples.
Cognola, Guido; Sebastiani, Lorenzo; Vagnozzi, Sunny; Zerbini, Sergio
2016-01-01
We consider the Nojiri-Odintsov covariant Horava-like gravitational model, where diffeomorphism invariance is broken dynamically via a non-standard coupling to a perfect fluid. The theory allows to address some of the potential instability problems present in Horava-Lifshitz gravity due to explicit diffeomorphism invariance breaking. The fluid is instead constructed from a scalar field constrained by a Lagrange multiplier. This construction allows to identify the scalar field with the mimetic field of the recently proposed mimetic gravity. Subsequently, we thoroughly explore the consequences of this identification. By adding a potential for the scalar field, we show how one can reproduce a number of interesting cosmological scenarios. We then turn to the study of perturbations around a flat FLRW background, showing that the fluid in question behaves as an irrotational fluid, with zero sound speed. To address this problem, we consider a modified version of the theory, adding higher derivative terms in a way wh...
Inhomogeneous Big Bang Cosmology
Wagh, S M
2002-01-01
In this letter, we outline an inhomogeneous model of the Big Bang cosmology. For the inhomogeneous spacetime used here, the universe originates in the infinite past as the one dominated by vacuum energy and ends in the infinite future as the one consisting of "hot and relativistic" matter. The spatial distribution of matter in the considered inhomogeneous spacetime is {\\em arbitrary}. Hence, observed structures can arise in this cosmology from suitable "initial" density contrast. Different problems of the standard model of Big Bang cosmology are also resolved in the present inhomogeneous model. This inhomogeneous model of the Big Bang Cosmology predicts "hot death" for the universe.
Self-tuning Solution of Cosmological Constant in RS-II Model and Goldstone Boson
Kim, J E
2001-01-01
I give a review on the self-tuning solution of the cosmological constant in a 5D RS-II model using a three index antisymmetric tensor field $A_{MNP}$. The three index antisymmetric tensor field can be the fundamental one appearing in 11D supergravity. Also, the dual of its field strength $H_{MNPQ}$, being a massless scalar, may be interpreted as a Goldstone boson of some spontaneously broken global symmetry.
On the Tensor Field Inflation in the GR Homogeneous Cosmological Model
Kazarian, Poghos F.
2000-01-01
The homogeneous cosmological model in GR is proposed, where the vacuum energy, which can cause the inflation, is described by tensor field rather than by commonly used in inflationary scenarios scalar field. It is shown that if the initial values of the field are sufficiently big (comparable with the Planck units), under the condition of the tensor field's slow change in the beginning the regime of the quasiexponential inflation can exist. Numerical solutions for the inflationary stage are ob...
Anisotropic Dark Energy Bianchi Type III Cosmological Models in Brans Dicke Theory of Gravity
Shamir, M Farasat; 10.1139/P2012-007
2012-01-01
The main purpose of this paper is to explore the solutions of Bianchi type $III$ cosmological model in Brans Dicke theory of gravity in the background of anisotropic dark energy. We use the assumption of constant deceleration parameter and power law relation between scalar field $\\phi$ and scale factor $a$ to find the solutions. The physical behavior of the solutions has been discussed using some physical quantities.
A TEST OF COSMOLOGICAL MODELS USING HIGH-z MEASUREMENTS OF H(z)
Energy Technology Data Exchange (ETDEWEB)
Melia, Fulvio [Department of Physics, The Applied Math Program, and Department of Astronomy, The University of Arizona, AZ 85721 (United States); McClintock, Thomas M., E-mail: fmelia@email.arizona.edu, E-mail: tmcclintock89@gmail.com [Department of Physics, The University of Arizona, AZ 85721 (United States)
2015-10-15
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 R{sub h} = 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 R{sub h} = 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.
On the existence of anisotropic cosmological models in higher order theories of gravity
Middleton, Jonathan
2010-01-01
Abstract We investigate the behaviour on approach to the initial singularity in higher-order extensions of general relativity by finding exact cosmological solutions for a wide class of models in which the Lagrangian is allowed to depend nonlinearly upon the three possible linear and quadratic scalars built from the Riemann tensor ; R, R ab R ab and R abcd R abcd. We present new anisotropic vacuum solutions analagous to the Kasner solutions of general relativity and extend previous results...
Cosmological models with interacting components and mass-varying neutrinos
Collodel, Lucas G
2012-01-01
A model for a homogeneous and isotropic spatially flat Universe, composed of baryons, radiation, neutrinos, dark matter and dark energy is analyzed. We infer that dark energy (considered to behave as a scalar field) interacts with dark matter (either by the Wetterich model, or by the Anderson and Carroll model) and with neutrinos by a model proposed by Brookfield et al.. The latter is understood to have a mass-varying behavior. We show that for a very-softly varying field, both interacting models for dark matter give the same results. The models reproduce the expected red-shift performances of the present behavior of the Universe.
Burbidge, Geoffrey
2008-01-01
This meeting is entitled "A Century of Cosmology." But most of the papers being given here are based on work done very recently and there is really no attempt being made to critically review what has taken place in the last 90 or 100 years. Instead, in general the participants accept without question that cosmology equates to "hot big bang cosmology" with all of its bells and whistles. All of the theory and the results obtained from observations are interpreted on the assumption that this extremely popular model is the correct one, and observers feel that they have to interpret its results in terms of what this theory allows. No one is attempting to seriously test the model with a view to accepting it or ruling it out. They are aware, as are the theorists, that there are enough free parameters available to fix up almost any model of the type. The current scheme given in detail for example by Spergel et al (206, 2007) demonstrates this. How we got to this stage is never discussed, and little or no attention is...
Exact string theory model of closed timelike curves and cosmological singularities
Johnson, Clifford V.; Svendsen, Harald G.
2004-12-01
We study an exact model of string theory propagating in a space-time containing regions with closed timelike curves (CTCs) separated from a finite cosmological region bounded by a big bang and a big crunch. The model is an nontrivial embedding of the Taub-NUT geometry into heterotic string theory with a full conformal field theory (CFT) definition, discovered over a decade ago as a heterotic coset model. Having a CFT definition makes this an excellent laboratory for the study of the stringy fate of CTCs, the Taub cosmology, and the Milne/Misner-type chronology horizon which separates them. In an effort to uncover the role of stringy corrections to such geometries, we calculate the complete set of α' corrections to the geometry. We observe that the key features of Taub-NUT persist in the exact theory, together with the emergence of a region of space with Euclidean signature bounded by timelike curvature singularities. Although such remarks are premature, their persistence in the exact geometry is suggestive that string theory is able to make physical sense of the Milne/Misner singularities and the CTCs, despite their pathological character in general relativity. This may also support the possibility that CTCs may be viable in some physical situations, and may be a natural ingredient in pre-big bang cosmological scenarios.
Non-linear structure formation in the "Running FLRW" cosmological model
Bibiano, Antonio
2016-01-01
We present a suite of cosmological N-body simulations describing the "Running Friedmann-Lema{\\"i}tre-Robertson-Walker" (R-FLRW) cosmological model. This model is based on quantum field theory in a curved space-time and extends {\\Lambda}CDM with a time-evolving vacuum density, {\\Lambda}(z), and time-evolving gravitational Newton's coupling, G(z). In this paper we review the model and introduce the necessary analytical treatment needed to adapt a reference N-body code. Our resulting simulations represent the first realisation of the full growth history of structure in the R-FLRW cosmology into the non-linear regime, and our normalisation choice makes them fully consistent with the latest cosmic microwave background data. The post-processing data products also allow, for the first time, an analysis of the properties of the halo and sub-halo populations. We explore the degeneracies of many statistical observables and discuss the steps needed to break them. Furthermore, we provide a quantitative description of the...
LRS Bianchi Type II Massive String Cosmological Models with Magnetic Field in Lyra's Geometry
Directory of Open Access Journals (Sweden)
Raj Bali
2013-01-01
Full Text Available Bianchi type II massive string cosmological models with magnetic field and time dependent gauge function ( in the frame work of Lyra's geometry are investigated. The magnetic field is in -plane. To get the deterministic solution, we have assumed that the shear ( is proportional to the expansion (. This leads to , where and are metric potentials and is a constant. We find that the models start with a big bang at initial singularity and expansion decreases due to lapse of time. The anisotropy is maintained throughout but the model isotropizes when . The physical and geometrical aspects of the model in the presence and absence of magnetic field are also discussed.
Perfect fluid Bianchi Type-I cosmological models with time varying and
Indian Academy of Sciences (India)
J P Singh; R K Tiwari
2008-04-01
Bianchi Type-I cosmological models containing perfect fluid with time varying and have been presented. The solutions obtained represent an expansion scalar bearing a constant ratio to the anisotropy in the direction of space-like unit vector . Of the two models obtained, one has negative vacuum energy density, which decays numerically. In this model, we obtain ∼ 2, ∼ 44/ and ∼ -2 ( is the cosmic time) which is in accordance with the main dynamical laws for the decay of . The second model reduces to a static solution with repulsive gravity.
Rama, S Kalyana
2016-01-01
The dynamics of a (3 + 1) dimensional homogeneous anisotropic universe is modified by Loop Quantum Cosmology and, consequently, it has generically a big bounce in the past instead of a big-bang singularity. This modified dynamics can be well described by effective equations of motion. We generalise these effective equations of motion empirically to (d + 1) dimensions. The generalised equations involve two functions and may be considered as a class of LQC -- inspired models for (d + 1) dimensional early universe cosmology. As a special case, one can now obtain a universe which has neither a big bang singularity nor a big bounce but approaches asymptotically a `Hagedorn like' phase in the past where its density and volume remain constant. In a few special cases, we also obtain explicit solutions.
Rama, S. Kalyana
2016-12-01
The dynamics of a (3 + 1) dimensional homogeneous anisotropic universe is modified by loop quantum cosmology and, consequently, it has generically a big bounce in the past instead of a big-bang singularity. This modified dynamics can be well described by effective equations of motion. We generalise these effective equations of motion empirically to (d + 1) dimensions. The generalised equations involve two functions and may be considered as a class of LQC-inspired models for (d + 1) dimensional early universe cosmology. As a special case, one can now obtain a universe which has neither a big bang singularity nor a big bounce but approaches asymptotically a `Hagedorn like' phase in the past where its density and volume remain constant. In a few special cases, we also obtain explicit solutions.
Zentner, A R
2003-01-01
Improvements in observational techniques have transformed cosmology into a field inundated with ever-expanding, high-quality data sets and driven cosmology toward a standard model where the classic cosmological parameters are accurately measured. I briefly discuss some of the methods used to determine cosmological parameters, particularly primordial nucleosynthesis, the magnitude- redshift relation of supernovae, and cosmic microwave background anisotropy. I demonstrate how cosmological data can be used to complement particle physics and constrain extensions to the Standard Model. Specifically, I present bounds on light particle species and the properties of unstable, weakly-interacting, massive particles. Despite the myriad successes of the emerging standard cosmological model, unanswered questions linger. Numerical simulations of structure formation predict galactic central densities that are considerably higher than observed. They also reveal hundreds of satellites orbiting Milky Way-like galaxies while th...
Cosmological Constraints on the Modified Entropic Force Model
Wei, Hao
2010-01-01
Very recently, Verlinde considered a theory in which space is emergent through a holographic scenario, and proposed that gravity can be explained as an entropic force caused by changes in the information associated with the positions of material bodies. Then, motivated by the Debye model in thermodynamics which is very successful in very low temperatures, Gao modified the entropic force scenario. The modified entropic force (MEF) model is in fact a modified gravity model, and the universe can...
A note on a mimetic scalar-tensor cosmological model
Energy Technology Data Exchange (ETDEWEB)
Rabochaya, Yevgeniya; Zerbini, Sergio [Universita di Trento, Dipartimento di Fisica, Povo, Trento (Italy); TIFPA-INFN, Povo, Trento (Italy)
2016-02-15
A specific Hordenski scalar-gravity mimetic model is investigated within a FLWR space-time. The mimetic scalar field is implemented via a Lagrangian multiplier, and it is shown that the model has equations of motion formally similar to the original simpler mimetic matter model of Chamseddine-Mukhanov-Vikman. Several exact solutions describing inflation, bounces, and future-time singularities are presented and discussed. (orig.)
Global stability analysis for cosmological models with non-minimally coupled scalar fields
Skugoreva, Maria A; Vernov, Sergey Yu
2014-01-01
We explorer dynamics of cosmological models with a non-minimally coupled scalar field evolving on a spatially flat Friedmann-Lemaitre-Robertson-Walker background. We consider cosmological models including the Hilbert-Einstein curvature term and the $N$ degree monomial of the scalar field non-minimally coupled to gravity. The potential of the scalar field is the $n$ degree monomial or polynomial.We describe several qualitatively different types of dynamics depending on values of power indices $N$ and $n$. We identify that three main possible pictures correspond to $n2N$ cases. Some special features connected with the important cases of $N=n$ (including quadratic potential with quadratic coupling) and $n=2N$ (which share its asymptotics with the potential of the Higgs-driven inflation) are described separately. A global qualitative analysis allows us to cover most interesting cases of small $N$ and $n$ by a limiting number of phase-space diagrams. The influence of the cosmological constant to the global feature...
Models of quintessence coupled to the electromagnetic field and the cosmological evolution of alpha
Copeland, E. J.; Nunes, N. J.; Pospelov, M.
2004-01-01
We study the change of the effective fine structure constant in the cosmological models of a scalar field with a nonvanishing coupling to the electromagnetic field. Combining cosmological data and terrestrial observations we place empirical constraints on the size of the possible coupling and explore a large class of models that exhibit tracking behavior. The change of the fine structure constant implied by the quasar absorption spectra together with the requirement of tracking behavior impose a lower bound of the size of this coupling. Furthermore, the transition to the quintessence regime implies a narrow window for this coupling around 10-5 in units of the inverse Planck mass. We also propose a nonminimal coupling between electromagnetism and quintessence which has the effect of leading only to changes of alpha determined from atomic physics phenomena, but leaving no observable consequences through nuclear physics effects. In doing so we are able to reconcile the claimed cosmological evidence for a changing fine structure constant with the tight constraints emerging from the Oklo natural nuclear reactor.
Brihaye, Yves; Hartmann, Betti
2005-01-01
We construct solutions of an Einstein Yang Mills system including a cosmological constant in 4 + n spacetime dimensions, where the n-dimensional manifold associated with the extra dimensions is taken to be Ricci flat. Assuming the matter and metric fields to be independent of the n extra coordinates, a spherical symmetric ansatz for the fields leads to a set of coupled ordinary differential equations. We find that for n > 1 only solutions with either one non-zero Higgs field or with all Higgs fields constant and zero gauge field function (corresponding to a Wu Yang-type ansatz) exist. We give the analytic solutions available in this model. These are 'embedded' Abelian solutions with a diverging size of the manifold associated with the extra n dimensions. Depending on the choice of parameters, these latter solutions either represent naked singularities or they possess a single horizon. We also present solutions of the effective four-dimensional Einstein Yang Mills Higgs-dilaton model, where the higher-dimensional cosmological constant induces a Liouville-type potential. The solutions are non-Abelian solutions with diverging Higgs fields, which exist only up to a maximal value of the cosmological constant.
KiDS-450: Testing extensions to the standard cosmological model
Joudaki, Shahab; Blake, Chris; Choi, Ami; de Jong, Jelte; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Hoekstra, Henk; Joachimi, Benjamin; Klaes, Dominik; Köhlinger, Fabian; Kuijken, Konrad; McFarland, John; Miller, Lance; Schneider, Peter; Viola, Massimo
2016-01-01
We test extensions to the standard cosmological model with weak gravitational lensing tomography using 450 deg$^2$ of imaging data from the Kilo Degree Survey (KiDS). In these extended cosmologies, which include massive neutrinos, nonzero curvature, evolving dark energy, modified gravity, and running of the scalar spectral index, we also examine the discordance between KiDS and cosmic microwave background measurements from Planck. The discordance between the two datasets is largely unaffected by a more conservative treatment of the lensing systematics and the removal of angular scales most sensitive to nonlinear physics. The only extended cosmology that simultaneously alleviates the discordance with Planck and is at least moderately favored by the data includes evolving dark energy with a time-dependent equation of state (in the form of the $w_0-w_a$ parameterization). In this model, the respective $S_8 = \\sigma_8 \\sqrt{\\Omega_{\\rm m}/0.3}$ constraints agree at the $1\\sigma$ level, and there is `substantial c...
Free-streaming radiation in cosmological models with spatial curvature
Wilson, M. L.
1982-01-01
The effects of spatial curvature on radiation anisotropy are examined for the standard Friedmann-Robertson-Walker model universes. The effect of curvature is found to be very important when considering fluctuations with wavelengths comparable to the horizon. It is concluded that the behavior of radiation fluctuations in models with spatial curvature is quite different from that in spatially flat models, and that models with negative curvature are most strikingly different. It is therefore necessary to take the curvature into account in careful studies of the anisotropy of the microwave background.
A New Viable f(R) Model in the Light of Local Gravity Test and Late-time Cosmology
Nautiyal, Akhilesh; Patel, Avani
2016-01-01
We propose a new model of f (R) gravity containing Arctan function in the lagrangian. We show here that this model satisfies fifth force constraint unlike a similar model [1]. In addition to this, we carry out the fixed point analysis as well as comment on the existence of curvature singularity in this model. The cosmological evolution for this f (R) gravity model is also analyzed in the Friedmann Robertson Walker background. To understand observational significance of the model, cosmological parameters are obtained numerically and compared with those of Lambda cold dark matter ({\\Lambda}CDM) model. We also scrutinize the model with supernova data.
Cosmological Reflection of Particle Symmetry
Maxim Khlopov
2016-01-01
The standard model involves particle symmetry and the mechanism of its breaking. Modern cosmology is based on inflationary models with baryosynthesis and dark matter/energy, which involves physics beyond the standard model. Studies of the physical basis of modern cosmology combine direct searches for new physics at accelerators with its indirect non-accelerator probes, in which cosmological consequences of particle models play an important role. The cosmological reflection of particle symmetr...
A Non - Singular Cosmological Model with Shear and Rotation
Goswami, G K; 10.1134/S0202289311040062
2011-01-01
We have investigated a non-static and rotating model of the universe with an imperfect fluid distribution. It is found that the model is free from singularity and represents an ever expanding universe with shear and rotation vanishing for large value of time.
Energy Technology Data Exchange (ETDEWEB)
Pfrommer, Christoph [Heidelberg Institute for Theoretical Studies, Schloss-Wolfsbrunnenweg 35, D-69118 Heidelberg (Germany); Chang, Philip; Broderick, Avery E., E-mail: christoph.pfrommer@h-its.org, E-mail: aeb@cita.utoronto.ca, E-mail: pchang@cita.utoronto.ca [Canadian Institute for Theoretical Astrophysics, 60 St. George Street, Toronto, ON M5S 3H8 (Canada)
2012-06-10
of the density power spectrum, {sigma}{sub 8}, and may reconcile SZ-inferred values with those by other cosmological probes even after allowing for a contribution due to patchy reionization. (3) Our redshift-dependent entropy floor increases the characteristic halo mass below which dwarf galaxies cannot form by a factor of approximately 10 (50) at mean density (in voids) over that found in models that include photoionization alone. This prevents the formation of late-forming dwarf galaxies (z {approx}< 2) with masses ranging from 10{sup 10} to 10{sup 11} M{sub Sun} for redshifts z {approx} 2 to 0, respectively. This may help resolve the 'missing satellite problem' in the Milky Way of the low observed abundances of dwarf satellites compared to cold dark matter simulations and may bring the observed early star formation histories into agreement with galaxy formation models. At the same time, it explains the 'void phenomenon' by suppressing the formation of galaxies within existing dwarf halos of masses <3 Multiplication-Sign 10{sup 10} M{sub Sun} with a maximum circular velocity <60 km s{sup -1} for z {approx}< 2, hence reconciling the number of dwarfs in low-density regions in simulations and the paucity of those in observations.
Brax, Philippe
2016-01-01
We investigate scalar-tensor theories where matter couples to the scalar field via a kinetically dependent conformal coupling. These models can be seen as the low-energy description of invariant field theories under a global Abelian symmetry. The scalar field is then identified with the Goldstone mode of the broken symmetry. It turns out that the properties of these models are very similar to the ones of ultralocal theories where the scalar-field value is directly determined by the local matter density. This leads to a complete screening of the fifth force in the Solar System and between compact objects, through the ultralocal screening mechanism. On the other hand, the fifth force can have large effects in extended structures with large-scale density gradients, such as galactic halos. Interestingly, it can either amplify or damp Newtonian gravity, depending on the model parameters. We also study the background cosmology and the linear cosmological perturbations. The background cosmology is hardly different f...