scholarly journals Higher dimensional perfect fluid cosmological model in general relativity with quadratic equation of state (EoS)

2021 ◽  
Keyword(s):  
General Relativity ◽  
Equation Of State ◽  
Cosmological Model ◽  
Perfect Fluid ◽  
Quadratic Equation ◽  
Higher Dimensional ◽  
Quadratic Equation Of State

scholarly journals Cosmological models through spatial Ricci-flow

2016 ◽  
Vol 13 (05) ◽  
pp. 1650069
Author(s):  
Ramesh Sharma
Keyword(s):  
Equation Of State ◽  
Perfect Fluid ◽  
Ricci Flow ◽  
Quadratic Equation ◽  
Space Time ◽  
Cosmological Models ◽  
Fluid Solution ◽  
Perfect Fluid Solution ◽  
Quadratic Equation Of State

We consider the synchronization of the Einstein’s flow with the Ricci-flow of the standard spatial slices of the Robertson–Walker space–time and show that associated perfect fluid solution has a quadratic equation of state and is either spherical and collapsing, or hyperbolic and expanding.

Aspects of nonflat FRW bouncing models with quadratic equation of state

2018 ◽  
Vol 33 (35) ◽  
pp. 1850213 ◽  
Author(s):  
Ashutosh Singh ◽  
Rakesh Raushan ◽  
R. Chaubey ◽  
T. Singh
Keyword(s):  
General Relativity ◽  
Equation Of State ◽  
Bulk Viscosity ◽  
Second Law Of Thermodynamics ◽  
Quadratic Equation ◽  
Energy Conditions ◽  
Second Law ◽  
Generalized Second Law ◽  
Quadratic Equation Of State

In this paper, we investigate the possibility of a nonsingular model of universe in the framework of general relativity in nonflat FRW geometries with quadratic equation of state and bulk viscosity. We study whether a nonsingular bounce requires violation of energy conditions. We discuss the thermodynamical aspects of the resulting models with equilibrium description. In particular, we discuss the validity of the generalized second law of thermodynamics for resulting cosmologies.

scholarly journals Anisotropic Standard Decelerating Cosmological Model with Quadratic Equation of State

2020 ◽  
Vol 08 (09) ◽  
pp. 1990-1998
Author(s):  
Mohammad Moksud Alam ◽  
Mohammed Aman Ullah ◽  
S M Erfanul Kabir Chowdhury
Keyword(s):  
Equation Of State ◽  
Cosmological Model ◽  
Quadratic Equation ◽  
Quadratic Equation Of State

scholarly journals A Cosmological Model Based on a Quadratic Equation of State Unifying Vacuum Energy, Radiation, and Dark Energy

2013 ◽  
Vol 2013 ◽  
pp. 1-20 ◽  
Author(s):  
Pierre-Henri Chavanis
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Model ◽  
Vacuum Energy ◽  
Quadratic Equation ◽  
Accelerated Expansion ◽  
Constant Density ◽  
Energy Radiation ◽  
Quadratic Equation Of State

We consider a cosmological model based on a quadratic equation of state (where is the Planck density and is the cosmological density) “unifying” vacuum energy, radiation, and dark energy. For , it reduces to leading to a phase of early accelerated expansion (early inflation) with a constant density equal to the Planck density  g/m3 (vacuum energy). For , we recover the equation of state of radiation . For , we get leading to a phase of late accelerated expansion (late inflation) with a constant density equal to the cosmological density  g/m3 (dark energy). The temperature is determined by a generalized Stefan-Boltzmann law. We show a nice “symmetry” between the early universe (vacuum energy + radiation) and the late universe (radiation + dark energy). In our model, they are described by two polytropic equations of state with index and respectively. Furthermore, the Planck density in the early universe plays a role similar to that of the cosmological density in the late universe. They represent fundamental upper and lower density bounds differing by 122 orders of magnitude. We add the contribution of baryonic matter and dark matter considered as independent species and obtain a simple cosmological model describing the whole evolution of the universe. We study the evolution of the scale factor, density, and temperature. This model gives the same results as the standard CDM model for , where is the Planck time and completes it by incorporating the phase of early inflation in a natural manner. Furthermore, this model does not present any singularity at and exists eternally in the past (although it may be incorrect to extrapolate the solution to the infinite past). Our study suggests that vacuum energy, radiation, and dark energy may be the manifestation of a unique form of “generalized radiation.” By contrast, the baryonic and dark matter components of the universe are treated as different species. This is at variance with usual models (quintessence, Chaplygin gas, ...) trying to unify dark matter and dark energy.

scholarly journals Bianchi type-III cosmological model with quadratic EoS in Lyra geometry

2018 ◽  
Vol 15 (11) ◽  
pp. 1850194 ◽  
Author(s):  
Mahbubur Rahman Mollah ◽  
Kangujam Priyokumar Singh ◽  
Pheiroijam Suranjoy Singh
Keyword(s):  
Equation Of State ◽  
Cosmological Model ◽  
Exact Solutions ◽  
Bianchi Type ◽  
Lyra Geometry ◽  
Quadratic Equation ◽  
Anisotropic Space ◽  
Field Equations ◽  
Type Iii ◽  
Quadratic Equation Of State

The paper deals with the investigation of a homogeneous and anisotropic space-time described by Bianchi type-III metric with perfect fluid in Lyra geometry setting. Exact solutions of Einstein’s field equations have been obtained under the assumption of quadratic equation of state (EoS) of the form [Formula: see text], where [Formula: see text] is a constant and strictly [Formula: see text]. The physical and geometrical aspects are also examined in detail.

scholarly journals Anisotropic cosmological dynamics in f(T) gravity in the presence of a perfect fluid

2019 ◽  
Vol 79 (10) ◽  
Author(s):  
Maria A. Skugoreva ◽  
Alexey V. Toporensky
Keyword(s):  
General Relativity ◽  
Equation Of State ◽  
Perfect Fluid ◽  
Matter Content ◽  
Cosmological Evolution ◽  
Anisotropic Universe ◽  
Anisotropic Solution ◽  
Cosmological Singularity ◽  
Hubble Parameters ◽  
The Universe

Abstract We consider the cosmological evolution of a flat anisotropic Universe in f(T) gravity in the presence of a perfect fluid. It is shown that the matter content of the Universe has a significant impact of the nature of a cosmological singularity in the model studied. Depending on the parameters of the f(T) function and the equation of state of the perfect fluid in question the well-known Kasner regime of general relativity can be replaced by a new anisotropic solution, or by an isotropic regime, or the cosmological singularity changes its nature to a non-standard one with a finite values of Hubble parameters. Six possible scenarios of the cosmological evolution for the model studied have been found numerically.

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