Primordial Density Perturbations and Reheating from Gravity

TL;DR

This paper explores how primordial density perturbations evolve in a modified gravity model during inflation, revealing unique oscillating behavior and a rapid reheating process that differ from standard inflationary theories.

Contribution

It introduces a simple ansatz for effective gravitational equations capturing quantum loop effects, leading to novel scalar perturbation dynamics and a natural reheating mechanism.

Findings

Scalar perturbations oscillate after inflation

The model predicts a fast reheating process

Perturbation evolution differs from conventional inflation

Abstract

We consider the presence and evolution of primordial density perturbations in a cosmological model based on a simple ansatz which captures -- by providing a set of effective gravitational field equations -- the strength of the enhanced quantum loop effects that can arise during inflation. After deriving the general equations that perturbations obey, we concentrate on scalar perturbations and show that their evolution is quite different than that of conventional inflationary models but still phenomenologically acceptable. The main reason for this novel evolution is the presence of an oscillating regime after the end of inflation which makes all super-horizon scalar modes oscillate. The same reason allows for a natural and very fast reheating mechanism for the universe.