Preheating in Generalized Einstein Theories

TL;DR

This paper investigates the preheating process in generalized Einstein theories, focusing on the amplification of metric and scalar field perturbations, and explores implications for gravitational and higher-dimensional physics.

Contribution

It extends previous preheating studies by including dilatonic/Brans-Dicke fields and metric perturbations, revealing super-horizon amplification effects.

Findings

Super-horizon perturbation amplification in dilaton/Brans-Dicke fields.

Oscillating Newton's constant with high frequency within the horizon.

Potential excitation of Kaluza-Klein modes in higher-dimensional theories.

Abstract

We study the preheating scenario in Generalized Einstein Theories, considering a class of such theories which are conformally equivalent to those of an extra field with a modified potential in the Einstein frame. Resonant creation of bosons from oscillating inflaton has been studied before in the context of general relativity taking also into account the effect of metric perturbations in linearized gravity. As a natural generalization we include the dilatonic/Brans-Dicke field without any potential of its own and in particular we study the linear theory of perturbations including the metric perturbations in the longitudinal gauge. We show that there is an amplification of the perturbations in the dilaton/Brans-Dicke field on super-horizon scales (k -> 0) due to the fluctuations in metric, thus leading to an oscillating Newton's constant with very high frequency within the horizon and with growing amplitude outside the horizon. We briefly mention the entropy perturbations generated by such fluctuations and also mention that there is a possibility to excite the Kaluza-Klein modes in the theories where the dilatonic/Brans-Dicke field is interpreted as a homogeneous field appearing due to the dimensional reduction from the higher dimensional theories.