Hidden regimes during preheating

TL;DR

This paper explores the various low energy regimes during preheating in scalar field models, revealing hidden regimes where one species influences another without appearing as a low energy mode, due to derivative couplings.

Contribution

It introduces the concept of hidden regimes in EFT of preheating, showing how derivative couplings create complex low energy behaviors and effective sound speeds.

Findings

Identification of scales where only one species appears as a low energy mode.

Discovery of non-trivial sound speeds indicating additional heavy fields.

Introduction of 'Hidden Regimes' where species influence each other's dispersion relations without being low energy modes.

Abstract

The Effective Field Theory (EFT) of Preheating with scalar fields, implies three types of derivative couplings between the inflaton and the reheating field. Two of these couplings lead to scales below which only one of the two species appear as the low energy modes. In this paper, the variety of low energy regimes in terms of the species they accommodate are explored by studying the scales introduced by the derivative couplings and the dispersion relations they lead to. It is noted that the EFT of two scalar fields can give rise to non-trivial sound speed for both the inflation and reheating sector even at scales where modes of both species propagate freely, suggesting the presence of additional heavy fields. The regimes where one of the species affects the dispersion relation of the other while not appearing as an effective mode itself, are named as "Hidden Regimes" during preheating.