Evolution of curvature perturbation in generalized gravity theories

TL;DR

This paper develops a simple formulation for the evolution of curvature perturbations during inflation in generalized gravity theories, accounting for non-ideal energy-momentum tensors influenced by fundamental quantum gravity corrections.

Contribution

It introduces a novel formulation of curvature perturbation evolution in generalized gravity, highlighting differences at inflation's end boundary due to non-ideal energy-momentum tensors.

Findings

Formulation of curvature perturbation evolution in generalized gravity

Identification of differences at inflation's end boundary

Implications for quantum gravity corrections during inflation

Abstract

Using the cosmological perturbation theory in terms of the delta-N formalism, we find the simple formulation of the evolution of the curvature perturbation in generalized gravity theories. Compared with the standard gravity theory, a crucial difference appears in the end-boundary of the inflationary stage, which is due to the non-ideal form of the energy momentum tensor that depends explicitly on the curvature scalar. Recent study shows that ultraviolet-complete quantum theory of gravity may be approximated by using a generalized gravity action. Our paper may give an important step in understanding the evolution of the curvature perturbation during inflation, where the energy momentum tensor may not be given by the ideal form due to the corrections from the fundamental theory.