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 RELATIVISTIC STELLAR MODEL ADMITTING A QUADRATIC EQUATION OF STATE

2013 ◽  
Vol 22 (13) ◽  
pp. 1350074 ◽  
Author(s):  
R. SHARMA ◽  
B. S. RATANPAL
Keyword(s):  
Equation Of State ◽  
Analytic Solution ◽  
Geometric Interpretation ◽  
Quadratic Equation ◽  
Stellar Model ◽  
Model Parameters ◽  
Spherically Symmetric ◽  
Quadratic Equation Of State ◽  
Anisotropic Star

A class of solutions describing the interior of a static spherically symmetric compact anisotropic star is reported. The analytic solution has been obtained by utilizing the Finch and Skea [Class. Quantum Grav.6 (1989) 467] ansatz for the metric potential grr which has a clear geometric interpretation for the associated background spacetime. Based on physical grounds, appropriate bounds on the model parameters have been obtained and it has been shown that the model admits an equation of state (EOS) which is quadratic in nature.

scholarly journals Stability and improved physical characteristics of relativistic compact objects arising from the quadratic term in $$p_r = \alpha \rho ^2 + \beta \rho - \gamma $$

2021 ◽  
Vol 81 (1) ◽  
Author(s):  
S. Thirukkanesh ◽  
Robert S. Bogadi ◽  
Megandhren Govender ◽  
Sibusiso Moyo
Keyword(s):  
Equation Of State ◽  
Gravitational Potential ◽  
Equations Of State ◽  
Quadratic Equation ◽  
Physical Characteristics ◽  
Compact Objects ◽  
Quadratic Term ◽  
Stellar Objects ◽  
Quadratic Equation Of State ◽  
The Stability

AbstractWe investigate the stability and enhancement of the physical characteristics of compact, relativistic objects which follow a quadratic equation of state. To achieve this, we make use of the Vaidya–Tikekar metric potential. This gravitational potential has been shown to be suitable for describing superdense stellar objects. Pressure anisotropy is also a key feature of our model and is shown to play an important role in maintaining stability. Our results show that the combination of the Vaidya–Tikekar gravitational potential used together with the quadratic equation of state provide models which are favourable. In comparison with other equations of state, we have shown that the quadratic equation of state mimics the colour-flavour-locked equation of state more closely than the linear equation of state.

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