Can f(R) gravity isotropise a pre-bounce contracting universe?

Abstract

Abstract We address the important issue of isotropisation of a pre-bounce contracting phase in f(R) gravity, which would be relevant to constructing any viable nonsingular bouncing scenario in f(R) gravity. The main motivation behind this work is to investigate whether the f(R) gravity, by itself, can isotropise a contracting universe starting initially with small anisotropy without incorporating a super-stiff or non-ideal fluid, impossible in general relativity. Considering Bianchi I cosmology and employing a dynamical system analysis, we see that this is not possible for R n (n > 1) and R + αR 2 (α > 0) theory, but possible for 1/α eαR (α > 0) theory. On the other hand, if one does not specify an f(R) theory a priori but demands a cosmology smoothly connecting an ekpyrotic contraction phase to a nonsingular bounce, the ekpyrotic phase may not fulfil the condition for isotropisation and physically viability simultaneously.