Distortion of the standard cosmology in R+R^2 theory

TL;DR

This paper explores how R+R^2 gravity modifies early universe cosmology, affecting inflation, particle production, and primordial structures, with potential observable consequences for black holes and baryogenesis.

Contribution

It provides a detailed analysis of the universe's evolution in R+R^2 gravity, highlighting deviations from standard cosmology during inflation and their implications.

Findings

Inflation driven by large initial curvature scalar R.

Gravitational particle production causes a graceful exit from inflation.

Early universe evolution significantly differs from standard cosmology until curvature oscillations decay.

Abstract

Universe history in $R^2$-gravity is studied from "beginning" up to the present epoch. It is assumed that initially the curvature scalar $R$ was sufficiently large to induce the proper duration of inflation. Gravitational particle production by the oscillating $R(t)$ led to a graceful exit from inflation, but the cosmological evolution in the early universe was drastically different from the standard one till the universe age reached the value of the order of the inverse decay rate of the oscillating curvature $R(t)$. This deviation from the standard cosmology might have a noticeable impact on the formation of primordial black holes and baryogenesis. At later time, after exponential decay of the curvature oscillations, cosmology may return to normality.