R Chaubey
Articles written in Pramana – Journal of Physics
Volume 67 Issue 3 September 2006 pp 415-428 Research Articles
Bianchi type-V model with a perfect fluid and A-term
A self-consistent system of gravitational field with a binary mixture of perfect fluid and dark energy given by a cosmological constant has been considered in Bianchi Type-V universe. The perfect fluid is chosen to be obeying either the equation of state
Volume 67 Issue 6 December 2006 pp 1037-1041 Research Articles
Cosmic no-hair conjecture in scalar-tensor theories
We have shown that, within the context of scalar-tensor theories, the anisotropic Bianchi-type cosmological models evolve towards de Sitter Universe. A similar result holds in the case of cosmology in Lyra manifold. Thus the analogue of cosmic no-hair theorem of Wald [1] hold in both the cases. In fact, during inflation there is no difference between scalar-tensor theories, Lyra’s manifold and general relativity (GR).
Volume 88 Issue 4 April 2017 Article ID 0061 Research Article
R CHAUBEY A K SHUKLA RAKESH RAUSHAN
The general class of Bianchi cosmological models with dark energy in the form of modified Chaplygin gas with variable $\Lambda$ and $G$ and bulk viscosity have been considered. We discuss three types of average scalefactor by using a special law for deceleration parameter which is linear in time with negative slope. The exact solutions to the corresponding field equations are obtained. We obtain the solution of bulk viscosity ($\xi$ ), cosmologicalconstant ($\Lambda$), gravitational parameter ($G$) and deceleration parameter ($q$) for different equations of state. The model describes an accelerating Universe for large value of time $t$ , wherein the effective negative pressure induced by Chaplygin gas and bulk viscous pressure are driving the acceleration.
Volume 88 Issue 4 April 2017 Article ID 0065 Research Article
The anisotropic cosmological models in $f (R, T)$ gravity with $\Lambda (T)$
The general class of anisotropic Bianchi cosmological models in $f(R, T)$ modified theories of gravity with $\Lambda (T)$ has been considered. This paper deals with $f(R, T)$ modified theories of gravity, where the gravitational Lagrangian is given by an arbitrary function of Ricci scalar $R$ and the trace of the stress-energy tensor $T$ has been investigated for a specific choice of $f (R,T )$ = $f_{1}(R) + f_{2}(T)$. The exact solutions to the corresponding field equations are obtained in quadrature form. We have discussed three types of solutions of the average scale factor for the general class of Bianchi cosmological models by using a special law for deceleration parameter which is linear in time with a negative slope. The solutions to the Einstein field equations are obtained for three differentphysical viable cosmologies. All physical parameters are calculated and discussed in each model.
Volume 92 Issue 5 May 2019 Article ID 0079 Research Article
RAKESH RAUSHAN A K SHUKLA R CHAUBEY T SINGH
In this paper, we have studied the locally rotationally symmetric (LRS) Bianchi type-I cosmological model filled with a bulk viscous cosmological fluid in $f(R)$ gravity in the presence of time-varying gravitational and cosmological constant. We have used the power-law and intermediate scenario for scale factor to obtain thesolution of the field equations. The evolution of temperature of a viscous Universe is also analysed.
Volume 94, 2020
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