Cosmological models with constant deceleration parameter in Brans-Dicke theory

A detailed study of cosmological models with constant deceleration parameterq is undertaken in the framework of Brans-Dicke theory. These models are divided into two categories: (i) singular models with expansion driven by big-bang impulse, (ii) non-singlar models with expansion driven by creation of matter particles. Prigogine's hypothesis of creation of matter out of gravitational energy is analysed and extended to BD cosmology. To accommodate the creation of new particles, the universe is regarded as an open thermodynamical system and the energy conservation equation is modified with the incorporation of a creation pressure termp _c in the energy-momentum tensor . The exact solutions of the field equations of BD theory with are obtained using the power law relation=KR , which leads to models with constantq. The behaviour of the solutions is investigated for different range of values ofa. The role played by the BD scalar field and creation of matter particles in the expansion of the universe is investigated. It is found that one particular model with constantq has exponential expansion.     

Cosmological models in a Kaluza-Klein theory with variable rest mass

A general class of solutions is obtained for a homogeneous, spatially isotropic five-dimensional (5D) Kaluza-Klein theory with variable rest mass. These solutions generalize in the algebraic and physical sense the previously found solutions in the literature. The 4D spacetime sections of the solutions reduce to the Minkowski metric, K=0 Robertson-Walker metric with the equation of statep=np (p=pressure,n=constant sound speed,=energy density), and to the Robertson-Walker spacetime with steady-state metric. Some of the solutions, in different limits, show compactification of the fifth dimension. Some extensions of the model are discussed.     

Cosmological models

An LRS Bianchi type II cosmological model is built with a state equation that is a function of the cosmic timet. The ratiop/ is 1/3 whent 0 and is insignificant whent. Thus, the matter content behaves like radiation for smallt and like dust for larget.     

Cosmological models with constant deceleration parameter in Nordtvedt’s theory

Exact solutions of the field equations of Nordtvedt’s theory for spatially flat FRW models with constant deceleration parameter have been obtained. Singular solutions with (i) power-law (ii) exponential expansion have been studied in Nordtvedt’s theory where the coupling parameterω is a function of the scalar fieldφ.     

Cosmological Plebanski theory

We consider the cosmological symmetry reduction of the Plebanski action as a toy-model to explore, in this simple framework, some issues related to loop quantum gravity and spin-foam models. We make the classical analysis of the model and perform both path integral and canonical quantizations. As for the full theory, the reduced model admits two disjoint types of classical solutions: topological and gravitational ones. The quantization mixes these two solutions, which prevents the model from being equivalent to standard quantum cosmology. Furthermore, the topological solution dominates at the classical limit. We also study the effect of an Immirzi parameter in the model.     

Cosmological models in general relativity

LRS Bianchi type-I space-time filled with perfect fluid is considered here with deceleration parameter as variable. The metric potentialsA andB are functions of x as well as t. Assuming B′/B = f (x), where prime denotes differentiation with respect to x, it was found thatA = (l′/l)B andB = lS(t), wherel = f (x) andS is the scale factor which is a function of t only. The value of Hubble’s constantH ₀ was found to be less than half for non-flat model and is equal to 1.3 for a flat model     

Cosmological applications in Kaluza-Klein theory

The field equations of Kaluza–Klein (KK) theory have been applied in the domain of cosmology. These equations are solved for a flat universe by taking the gravitational and the cosmological constants as a function of time t. We use Taylor’s expansion of cosmological function, Λ(t), up to the first order of the time t. The cosmological parameters are calculated and some cosmological problems are discussed.     

Cosmological Coriolis fields in the Newton-Cartan theory

If the Newton-Cartan theory of gravitation is not restricted by a law of existence of absolute rotation, its statements for infinite systems may differ from those of Newton's classical theory through the existence of intrinsic (gravitational) Coriolis fields. Explicit examples are given.     

Cosmological models without singularities

A previously studied theory of gravitation in flat space-time [Petry, W. (1981).Gen. Rel. Grav. 13, 865] is applied to homogeneous and isotropic cosmological models. There exist two different classes of models without singularities: (i) ever-expanding models, (ii) oscillating models. The first class contains models with hot big bang. For these models we get at the beginning of the universe—in contrast to Einstein's theory—very high but finite densities of matter and radiation with a big bang of very short duration. After short time these models pass into the homogeneous and isotropic models of Einstein's theory with spatial curvature equal zero and cosmological constant 0.     

Cosmological models with rotation

Nonstationary and stationary cosmological models with rotation and the Bianchi IX metric are constructed within the general relativity theory. A comoving anisotropic liquid and non-comoving “dust-like liquid” are the sources of gravitation in one case, while a comoving anisotropic, non-comoving “dust-like liquid”, and pure radiation - in the other. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 33–37, August, 2008.     

Cosmological perturbation theory in slow-roll spacetimes

We present a gauge-invariant argument that a nonlocal measure of second-order metric and matter perturbations dominates that of linear fluctuations in its effect on the gravitational field in "slow-rolling" spacetimes.     

Cosmological applications in Kaluzaben Klein theory

The field equations of Kaluza-Klein (KK) theory have been applied in the domain of cosmology. These equations are solved for a flat universe by taking the gravitational and the cosmological constants as a function of time t. We use Taylor's expansion of cosmological function, Λ(t), up to the first order of the time t. The cosmological parameters are calculated and some cosmological problems are discussed.     

Cosmological models and Non-denumerable singularities

A review of the standard cosmological models shows that the positive cosmological constant gives rise to exponential increase in spatial extension. Such an increase is contradictory if extended over infinite future time, since even in an infinite universe there can only be a denumerable infinity of finite spatial units. The argument against exponential expansion is among the processes forbidden by the steady-state postulate of MacMillan.     

Cosmological Friedman models with the charged vacuum

Exact solutions corresponding to the stable charged vacuum are obtained for cosmological Friedman models with a charged scalar field. It is demonstrated that the presence of a massive vector field for the vacuum changes the law of expansion at early stages of evolution of the universe. A method for construction of solutions with the charged vacuum for an O(N) invariant scalar multiplet is given.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 19–24, December, 1985.     

Cosmological models with Yang-Mills fields

Cosmological models with an SU(2) Yang-Mills field are studied. For a specific model with a minimally coupled Yang-Mills Lagrangian, which includes an arbitrary function of the second-order term and a fourth-order term, a corresponding reconstruction program is proposed. It is shown that the model with minimal coupling has no de Sitter solutions, for any nontrivial function of the second-order term. To get de Sitter solutions, a gravitational model with nonminimally coupled Yang-Mills fields is then investigated. It is shown that the model with non-minimal coupling has in fact a de Sitter solution, even in absence of the cosmological constant term.     

Cosmological constraints on supergravity models

We delineate the domain of supersymmetry breaking parameters in minimal supergravity models for which the cosmological relic photino density is no larger than the closure density. Demanding that the relic density equal the closure density as suggested by inflationary cosmology suggests $\text{m}{}_{\mathrm{<mtext>q</mtext><mtext>?</mtext>}}\text{～ 42}\text{GeV}\text{+ 0.89 m}{}_{\mathrm{<mtext>g</mtext><mtext>?</mtext>}}$. We point out that several supergravity scenarios for the monojet events at the CERN $\text{p}$p Collider would yield a relic density considerably greater than the closure density.     

Cosmological constant in SUGRA models and the multiple-point principle

Physics of Atomic Nuclei - An attempt is made to explain the tiny order of magnitude of the cosmological constant in a model involvingt he following ingredients: supersymmetry breaking in N = 1...     

Cosmological models and latest observational data

In this note, we consider the observational constraints on some cosmological models by using the 307 Union type Ia supernovae (SNIa), the 32 calibrated gamma-ray bursts (GRBs) at z>1.4, the updated shift parameter R from WMAP 5-year data (WMAP5), and the distance parameter A of the measurement of the baryon acoustic oscillation (BAO) peak in the distribution of SDSS luminous red galaxies with the updated scalar spectral index n _s from WMAP5. The tighter constraints obtained here update the ones obtained previously in the literature.