Bulk viscous fluid cosmological models in f(R, T) gravity

In the literature, a number of modified theories have been discussed to explain early and late time expansion of the universe. In this context, f(R) gravity (R being the Ricci scalar) is the simplest and most popular modification of general relativity. Other modified theories like f(T) gravity, where T is the torsion has been proposed to overcome many problems in cosmology. Kaluza-Klein cosmological models in f(R, T) theory of gravity are investigated when the source of gravitation is the bulk viscous fluid. In this work, it is considered that the function f(R, T) as f(R, T) = R + 2f(T) or f(R, T) = f(1) (R) + f(2) (T). Such a choice of the functional f(R, T) leads to an evolving effective cosmological constant Lambda, which depends on the stress energy tensor. f(1) (R) and f(2) (T) are arbitrary functions of R and T, respectively and f(R, T) = R f(T) may be considered to solve the field equations. We however do not consider the general case, but restrict ourselves to the following form f(R, T) = R + 2f(T), where f(T) is an arbitrary function of the trace of energy-momentum tensor of matter. The term 2f(T) in the gravitational action modified the gravitational interaction between matter and curvature. It is observed that the first case of the model be reduced to effective stiff fluid model of the universe while the second case gives general bulk viscous model of the universe. The exact solutions of the field equations are obtained. Keeping an eye on the accelerating nature of the universe in the present epoch, the dynamics and physical behaviour of the models are discussed. (C) 2016 Published by Elsevier B.V. on behalf of The Physical Society of the Republic of China (Taiwan).