Inflation and cosmological evolution with F (R, ) gravity theory

Abstract

In the last decade Planck PR4 data together with ground-based experimental data such as BK18, BAO and CMB lensing tightened constraint of the tensor-To-scalar ratio, starting form r < 0.14 to r < 0.032, while the spectral index lies within the range 0.9631 ≤ ns ≤ 0.9705. Viability of modified gravity theories, proposed as alternatives to the dark energy issue, should therefore be tested in the light of such new result. Here, we explore F(R,) gravity theory in regard to the early universe and show that it is not compatible with newly released constraints on r and ns simultaneously. Further, it also fails to produce a feasible radiation-dominated era. It therefore questions the justification of using the model for resolving the cosmic puzzle.