Early universe in view of a modified theory of gravity

TL;DR

This paper investigates the quantum and semi-classical evolution of the early universe within a generalized modified gravity framework, highlighting the roles of scalar fields, effective potentials, and the Gauss-Bonnet term in inflation and cosmic evolution.

Contribution

It introduces a generalized scalar-tensor gravity model with arbitrary functions, incorporating scalar curvature squared and Gauss-Bonnet terms, and explores inflationary dynamics without flow parameters.

Findings

Effective potential can replace flow parameters for inflation analysis.

Adding a cosmological constant helps stabilize the dilaton and supports inflation.

Gauss-Bonnet term influences late-time cosmic evolution.

Abstract

We study the quantum evolution of the early universe, its semi-classical analogue together with inflationary regime, in view of a generalized modified theory of gravity. The action is built by supplementing the non-minimally coupled scalar-tensor theory of gravity with scalar curvature squared term and a Gauss-Bonnet-dilatonic coupled term. It is generalized, since all the parameters are treated as arbitrary functions of the scalar field. It is interesting to explore the fact that instead of considering additional flow parameters, an effective potential serves the purpose of finding inflationary parameters. The dilaton stabilization issue appears here as a problem with reheating. Addition of a cosmological constant term alleviates the problem, and inflation is effectively driven by the vacuum energy density. Thus Gauss-Bonnet term might play a significant role in describing late-time cosmic evolution.