On adiabatic invariant in generalized Galileon theories

TL;DR

This paper demonstrates the existence of an adiabatic invariant in generalized Galileon theories during inflation, which helps estimate universe expansion and particle production despite violent oscillations.

Contribution

It introduces the concept of an adiabatic invariant in generalized Galileon theories, providing a new tool for analyzing inflationary dynamics with non-minimal couplings.

Findings

Adiabatic invariant exists in all generalized Galileon theories during inflaton oscillations.

The invariant aids in estimating the universe's expansion law.

It helps evaluate particle production rates during oscillations.

Abstract

We consider background dynamics of generalized Galileon theories in the context of inflation, where gravity and inflaton are non-minimally coupled to each other. In the inflaton oscillation regime, the Hubble parameter and energy density oscillate violently in many cases, in contrast to the Einstein gravity with minimally coupled inflaton. However, we find that there is an adiabatic invariant in the inflaton oscillation regime in any generalized Galileon theory. This adiabatic invariant is useful in estimating the expansion law of the universe and also the particle production rate due to the oscillation of the Hubble parameter.