• R CHAUBEY

      Articles written in Pramana – Journal of Physics

    • Bianchi type-V model with a perfect fluid and A-term

      T Singh R Chaubey

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      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 p=γρ with γ ε |0,1| or a van der Waals equation of state. The role of A-term in the evolution of the Bianchi Type-V universe has been studied.

    • Cosmic no-hair conjecture in scalar-tensor theories

      T Singh R Chaubey

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      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).

    • The general class of Bianchi cosmological models with dark energy and variable $\Lambda$ and $G$ in viscous cosmology

      R CHAUBEY A K SHUKLA RAKESH RAUSHAN

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      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.

    • The anisotropic cosmological models in $f (R, T)$ gravity with $\Lambda (T)$

      R CHAUBEY A K SHUKLA

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      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.

    • Locally rotationally symmetric Bianchi type-I cosmological model with dynamical $Lambda$ and $G$ in $f (R)$ gravity

      RAKESH RAUSHAN A K SHUKLA R CHAUBEY T SINGH

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      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.

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