Natural entropy production in an inflationary model for a polarized vacuum

Though entropy production is forbidden in standard FRW Cosmology, Berman and Som presented a simple inflationary model where entropy production by bulk viscosity, during standard inflation without ad hoc pressure terms can be accommodated with Robertson–Walker’s metric, so the requirement that the early Universe be anisotropic is not essential in order to have entropy growth during inflationary phase, as we show. Entropy also grows due to shear viscosity, for the anisotropic case. The intrinsically inflationary metric that we propose can be thought of as defining a polarized vacuum, and leads directly to the desired effects without the need of introducing extra pressure terms.     

Inflationary solutions for anisotropic model in scalar-tensor theory

In this paper we have studied B-D theory and general scalar tensor theory of Gravitation for anisotropic cosmological model in the false vacuum state. The possibility of both exponential inflation and power function inflation are examined for constant or variable coupling parameter . Also asymptotic limit of the scalar field and are discussed.     

Dynamics of warm inflation with gauge fields in Bianchi type I universe model

In this paper, we study the dynamics of warm inflation in which slow-roll inflation is driven by non-Abelian gauge fields. To this end, we use the geometry of locally rotationally symmetric Bianchi type I universe model. We construct dynamical equations, i.e., first model field equation, energy conservation equations and equation of motion under slow-roll approximation. In order to discuss inflationary perturbations, we evaluate parameters like scalar and tensor power spectra as well as scalar and tensor spectral indices. We also evaluate inflaton, directional Hubble parameter, slow-roll and perturbation parameters as well as tensor-scalar ratio as a function of inflaton during intermediate and logamediate inflationary eras. It is concluded that anisotropic inflationary universe model with non-Abelian gauge fields remains compatible with WMAP7.     

Study of some chaotic inflationary models in $$ gravity

In this paper, we discuss an inflationary scenario via scalar field and fluid cosmology for an anisotropic homogeneous universe model in \(f(R)\) gravity. We consider an equation of state which corresponds to a quasi-de Sitter expansion and investigate the effect of the anisotropy parameter for different values of the deviation parameter. We evaluate potential models like linear, quadratic and quartic models which correspond to chaotic inflation. We construct the observational parameters for a power-law model of \(f(R)\) gravity and construct the graphical analysis of tensor–scalar ratio and spectral index which indicates the consistency of these parameters with Planck 2015 data.     

Warm anisotropic inflation with bulk viscous pressure in intermediate era

The aim of this paper is to study the warm inflation during intermediate era in the framework of locally rotationally symmetric Bianchi type I universe model. We assume that the universe is composed of inflaton and imperfect fluid having radiation and bulk viscous pressure. To this end, dynamical equations (first model field equation and energy conservation equations) under slow-roll approximation and in high dissipative regime are constructed. A necessary condition is developed for the realization of this anisotropic model. We assume both dissipation and bulk viscous coefficients variable as well as constant. We evaluate entropy density, scalar (tensor) power spectra, their corresponding spectral indices, tensor–scalar ratio and running of spectral index in terms of inflaton. These cosmological parameters are constrained using recent Planck and WMAP7 probe.     

Multidimensional cosmological models in effective string gravitation. II

We carry out an analysis of the exact solution obtained in the first part of this work for a homogeneous and anisotropic flat cosmological model in the general conformal representation of multidimensional low-energy string theory. We show that the singular solutions with power law of variation of the scale factors of maximally symmetric subspaces and scalar field are asymptotes of the general solution in early and late stages of evolution. We study the conditions under which models of exponential, extended, and violent inflation are realized. As an illustration of the general regularities we consider the specific example of an antisymmetric Kalb-Ramond field as a gravitational source. We demonstrate the possibility of dynamic compactification of the extra dimensions.Translated fromAstrofizika, Vol. 38, No. 3, 1995.     

Inflationary anisotropic phases with bianchi-I cosmic model

This paper is devoted to studying warm anisotropic inflation using modified Chaplygin gas in the context of the Bianchi-I comic model. We investigate the dynamics of the warm intermediate universe model in two distinct regimes, i.e., weak and strong regimes in the context of generalized dissipative coefficient. We formulate solutions of dissipation coefficient, inflaton field, scalar & tensor (S/T) power spectra, spectral index in an environment of slow-roll approximation to discuss the existence of warm weak and strong inflation and checked their viability in view of 2018 Planck data. It is seen through graphical representation that the condition for the existence of warm weak inflation is preserved only for $z=0$ and $z=1$ whereas in the case of the strong dissipative regime, the compatibility is achieved for $z=3$. The corresponding decay rates and the S/T are found to be consistent with the current observations.     

Exact Bianchi type-I cosmological model with matter in Brans-Dicke theory

In this paper an exact solution of the Brans-Dicke field equations in the presence of stiff matter is obtained for the Bianchi type-I cosmological space-time. The new solution represents an anisotropic homogeneous cosmological model which tends to anisotropic expansion. The behaviour of the solution near the singularities and late stages of the expansion is discussed.     

A cosmological model with both deceleration and acceleration

In this paper, we investigate a variation law for Hubble’s parameter in the curved, expanding background of spatially homogeneous, anisotropic Bianchi type I space-time. By choosing a particular form of the generalized Hubble’s parameter, which gives an early deceleration and late time acceleration for the anisotropic Bianchi type I cosmological model, we show that the model approaches isotropy and tends to a de Sitter universe at late times. The cosmological term asymptotically tends to a genuine cosmological constant and the solution is consistent with recent observations.     

Low scale Higgs inflation with Gauss–Bonnet coupling

Recent LHC data provides precise values of coupling constants of the Higgs field, however, these measurements do not determine its coupling with gravity. We explore this freedom to see whether Higgs field non-minimally coupled to Gauss–Bonnet term in 4-dimensions can lead to inflation generating the observed density fluctuations. We obtain analytical solution for this model and that the exit of inflation (with a finite number of e-folding) demands that the energy scale of inflation is close to Electro-weak scale. We compare the scalar and tensor power spectrum of our model with PLANCK data and discuss its implications.     

Incoherent scatter spectrum of ionospheric plasma with an anisotropic temperature ion distribution

The expression of anisotropic temperature ion distribution function under the 13-moment approximation is obtained by solving a set of moment equations based on the Boltzmann equation for a relaxation collision model and with consideration of the anisotropic temperature ion distribution. And the incoherent scatter spectrum with an anisotropic temperature ion distribution is simulated in different directions based on the electromagnetic radiation theory of Sheffield. The effects of different electrical field strengths, ratios of electron temperature to ion temperature, and ion-neutral collision frequencies on the incoherent scatter spectrum are all discussed. Finally, the value of theoretical simulation is compared with the measured value of incoherent scattering spectrum. The result show that the incoherent scatter spectrum of ions seriously deviates from the form of the Maxwellian distribution in the equilibrium state. This phenomenon can be attributed to the effects of anisotropic temperature ion distribution, the larger convection electric field, and other factors in high latitude ionosphere.     

Plane symmetric vacuum bianchi type I cosmological model in Brans-Dicke theory

The paper presents an exact solution of the vacuum Brans-Dicke field equations for the metric tensor of a spatially homogeneous and anisotropic cosmological model. The Kasner metric is shown as a special case. Some physical properties of the model are discussed.     

Compact models with regular charge distributions

We model a compact relativistic body with anisotropic pressures in the presence of an electric field. The equation of state is barotropic, with a linear relationship between the radial pressure and the energy density. Simple exact models of the Einstein–Maxwell equations are generated. A graphical analysis indicates that the matter and electromagnetic variables are well behaved. In particular, the proper charge density is regular for certain parameter values at the stellar center unlike earlier anisotropic models in the presence of charge. We show that the electric field affects the mass of stellar objects and the observed mass for a particular binary pulsar is regained. Our models contain previous results of anisotropic charged matter with a linear equation of state for special parameter values.     

Distortion of the spectrum of the microwave background radiation in an anisotropic universe

Distortion of spectrum of the cosmic microwave background due to anisotropic expansion is discussed. We consider an anisotropic cosmological model with a secondary re-heating and re-ionization. After the secondary re-heating distribution of photons momenta becomes isotropic but the spectrum becomes slightly different from that of black body.     

Dynamics of Kantowski-Sachs universe with magnetized anisotropic Dark Energy

Kantowski-Sachs cosmological model in the presence of magnetized anisotropic dark energy is investigated. The energy-momentum tensor consists of anisotropic fluid with anisotropic EoS p=ωρ and a uniform magnetic field of energy density ρ _B . We obtain exact solutions to the field equations using the condition that expansion is proportional to the shear scalar. The physical behavior of the model is discussed with and without magnetic field. We conclude that universe model as well as anisotropic fluid does not approach isotropy through the evolution of the universe.     

An Exact Anisotropic Quark Star Model

We present an exact analytical solution of the gravitational field equations describing a static spherically symmetric anisotropic quark matter distribution. The radial pressure inside the star is assumed to obey a linear equation of state, while the tangential pressure is a complicated function of the radial coordinate. In order to obtain the general solution of the field equations a particular density profile inside the star is also assumed. The anisotropic pressure distribution leads to an increase in the maximum radius and mass of the quark star, which in the present model is around three solar masses.     

Charged anisotropic models for quark stars

We perform a detailed physical analysis for a class of exact solutions for the Einstein–Maxwell equations. The linear equation of state consistent with quark stars has been incorporated in the model. The physical analysis of the exact solutions is performed by considering the charged anisotropic stars for the particular nonsingular exact model obtained by Maharaj, Sunzu and Ray. In performing such an analysis we regain masses obtained by previous researchers for isotropic and anisotropic matter. It is also indicated that other masses and radii may be generated which are in acceptable ranges consistent with observed values of stellar objects. A study of the mass-radius relation indicates the effect of the electromagnetic field and anisotropy on the mass of the relativistic star.     

Validity of the 'conservation law' in the evolution of cosmological perturbations

It is shown that the 'conservation law' for metric fluctuations with long wavelengths is indeed applicable for growing modes of perturbations, which are of interest in cosmology, in spite of recent criticism. This is demonstrated both by general arguments and by presenting an explicitly solvable toy model for the evolution of metric perturbations during inflation.     

Dynamics of Bianchi I universe with magnetized anisotropic Dark Energy

We study Bianchi type I cosmological model in the presence of magnetized anisotropic dark energy. The energy-momentum tensor consists of anisotropic fluid with anisotropic EoS p=ω ρ and a uniform magnetic field of energy density ρ _B . We obtain exact solutions to the field equations using the condition that expansion is proportional to the shear scalar. The physical behavior of the model is discussed with and without magnetic field. We conclude that universe model as well as anisotropic fluid do not approach isotropy through the evolution of the universe.     

Magnetized cosmological model in Lyra manifold

A spatially-homogeneous and anisotropic magnetized cosmological model in Lyra's manifold is obtained when the source of the gravitational field is a perfect fluid distribution. The magnetic field is due to an electric current produced along thex-axis. The physical behaviour of the model is discussed.