Acceleration of the universe in the Einstein frame of a metric-affine f(R) gravity

TL;DR

This paper demonstrates that a specific metric-affine f(R) gravity model in the Einstein frame can account for both inflation and late-time cosmic acceleration, with implications for matter effects and energy density scaling.

Contribution

It introduces a novel f(R) gravity formulation with mixed powers of R that explains cosmic acceleration phenomena in the Einstein frame.

Findings

Inflation and acceleration driven by L(R) with positive and negative R powers.

Matter effects weaken at late times, approaching 3/4 of original strength.

Matter energy density scales similarly to mbda-CDM when ppa*psilon << lpha.

Abstract

We show that inflation and current cosmic acceleration can be generated by a metric-affine f(R) gravity formulated in the Einstein conformal frame, if the gravitational Lagrangian L(R) contains both positive and negative powers of the curvature scalar R. In this frame, we give the equations for the expansion of the homogeneous and isotropic matter-dominated universe in the case L(R)=R+{R^3}/{\beta^2}-{\alpha^2}/{3R}, where \alpha and \beta are constants. We also show that gravitational effects of matter in such a universe at very late stages of its expansion are weakened by a factor that tends to 3/4, and the energy density of matter \epsilon scales the same way as in the \Lambda-CDM model only when \kappa*\epsilon<<\alpha.