scholarly journals Anisotropic bulk viscous string cosmological models of the Universe under a time-dependent deceleration parameter

Pramana ◽  
2020 ◽  
Vol 94 (1) ◽  
Author(s):  
Archana Dixit ◽  
Rashid Zia ◽  
Anirudh Pradhan
Keyword(s):  
Deceleration Parameter ◽  
Cosmological Models ◽  
Time Dependent ◽  
Bulk Viscous ◽  
The Universe

Cosmological Models in Lyra Geometry with Linearly Varying Deceleration Parameter

2018 ◽  
Author(s):  
Kalyani Desikan
Keyword(s):  
Exact Solutions ◽  
Displacement Field ◽  
Deceleration Parameter ◽  
Lyra Geometry ◽  
Cosmological Models ◽  
Time Dependent ◽  
Linearly Varying Deceleration Parameter ◽  
Frw Model ◽  
Time Periods ◽  
The Universe

Cosmological models with linearly varying deceleration parameter in the cosmological theory based on Lyra’s geometry have been discussed. Exact solutions have been obtained for a spatially flat FRW model by considering a time dependent displacement field. We have also obtained the time periods during which the universe undergoes decelerated and accelerated expansions for a matter-dominated universe.

scholarly journals THE STRING COUPLING ACCELERATES THE EXPANSION OF THE UNIVERSE

2005 ◽  
Vol 14 (12) ◽  
pp. 2327-2333
Author(s):  
JOHN ELLIS ◽  
NIKOLAOS E. MAVROMATOS ◽  
DIMITRI V. NANOPOULOS
Keyword(s):  
String Theory ◽  
Deceleration Parameter ◽  
Cosmological Models ◽  
Rate Of Change ◽  
Negative Sign ◽  
Time Dependent ◽  
Expansion Of The Universe ◽  
Present Rate ◽  
The Universe

Generic cosmological models in non-critical string theory have a time-dependent dilaton background at a late epoch. The cosmological deceleration parameter q0 is given by the square of the string coupling, [Formula: see text], up to a negative sign. Hence, the expansion of the universe must accelerate eventually, and the observed value of q0 corresponds to [Formula: see text]. In this scenario, the string coupling is asymptotically free at large times, but its present rate of change is imperceptibly small.

scholarly journals LITTLE RIP COSMOLOGICAL MODELS WITH TIME-DEPENDENT EQUATION OF STATE

2012 ◽  
Vol 27 (36) ◽  
pp. 1250210 ◽  
Author(s):  
I. BREVIK ◽  
V. V. OBUKHOV ◽  
K. E. OSETRIN ◽  
A. V. TIMOSHKIN
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Models ◽  
Time Dependent ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Energy Models ◽  
Sitter Spacetime ◽  
The Universe ◽  
Far Future

Specific dark energy models, leading to the Little Rip (LR) cosmology in the far future, are investigated. Conditions for the occurrence of LR in terms of the parameters present in the proposed equation of state for the dark energy cosmic fluid are studied. Estimates about the time needed before the occurrence of the small singularity in the standard LR model in which the universe approaches the de Sitter spacetime asymptotically, are given.

scholarly journals A dark energy quintessence model of the universe

2019 ◽  
Vol 35 (04) ◽  
pp. 2050002
Author(s):  
G. K. Goswami ◽  
Anirudh Pradhan ◽  
A. Beesham
Keyword(s):  
Dark Energy ◽  
Deceleration Parameter ◽  
Cosmological Parameters ◽  
Hubble Constant ◽  
Time Dependent ◽  
Observational Constraints ◽  
History Of ◽  
Flrw Universe ◽  
The Universe ◽  
Quintessence Model

In this paper, we have presented a model of the Friedmann–Lemaitre–Robertson–Walker (FLRW) universe filled with matter and dark energy (DE) fluids by assuming an ansatz that deceleration parameter (DP) is a linear function of the Hubble constant. This results in a time-dependent DP having decelerating–accelerating transition phase of the universe. This is a quintessence model [Formula: see text]. The quintessence phase remains for the period [Formula: see text]. The model is shown to satisfy current observational constraints. Various cosmological parameters relating to the history of the universe have been investigated.

Bulk viscous cosmological models of universe with variable deceleration parameter in Lyra’s Manifold

2009 ◽  
Vol 321 (3-4) ◽  
pp. 233-239 ◽  
Author(s):  
N. Ibotombi Singh ◽  
S. Romaleima Devi ◽  
S. Surendra Singh ◽  
A. Sumati Devi
Keyword(s):  
Deceleration Parameter ◽  
Cosmological Models ◽  
Variable Deceleration Parameter ◽  
Lyra’S Manifold ◽  
Bulk Viscous

scholarly journals Λ-CDM UNIVERSE: A PHENOMENOLOGICAL APPROACH WITH MANY POSSIBILITIES

2008 ◽  
Vol 17 (02) ◽  
pp. 301-309 ◽  
Author(s):  
UTPAL MUKHOPADHYAY ◽  
SAIBAL RAY ◽  
S. B. DUTTA CHOUDHURY
Keyword(s):  
Equation Of State ◽  
Phenomenological Model ◽  
Deceleration Parameter ◽  
State Parameter ◽  
Phenomenological Approach ◽  
Time Dependent ◽  
Equation Of State Parameter ◽  
Dependent Form ◽  
Age Of The Universe ◽  
The Universe

A time-dependent phenomenological model of Λ, viz. [Formula: see text], is selected to investigate the Λ-CDM cosmology. The time-dependent form of the equation-of-state parameter ω is derived and it has been possible to obtain the sought-for flip of sign of the deceleration parameter q. The present age of the Universe, calculated for some specific values of the parameters, agrees very well with the observational data.

DECELERATING CAUSAL BULK VISCOUS COSMOLOGICAL MODELS

2000 ◽  
Vol 09 (02) ◽  
pp. 97-110 ◽  
Author(s):  
T. HARKO ◽  
M. K. MAK
Keyword(s):  
Relaxation Time ◽  
Bulk Viscosity ◽  
Viscosity Coefficient ◽  
State Equation ◽  
Cosmological Models ◽  
Boltzmann Gas ◽  
Bulk Viscous ◽  
Barotropic Equation ◽  
Bulk Viscosity Coefficient ◽  
The Universe

The dynamics of a causal bulk viscous cosmological fluid filled flat constantly decelerating noninflationary Robertson–Walker spacetime is considered. The matter component of the Universe is assumed to satisfy a linear barotropic equation of state and the state equation of the small temperature Boltzmann gas. The resulting cosmological models satisfy the condition of smallness of the viscous stress. The evolution of the relaxation time, temperature, bulk viscosity coefficient and comoving entropy of the dissipative cosmological fluid are obtained by assuming several bulk viscosity coefficient-relaxation time relations.

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