Toward an Effective Field Theory Approach to Reheating

TL;DR

This paper explores applying Effective Field Theory to inflationary reheating, developing new models and predictions for gravitational waves, while addressing theoretical limitations of previous EFT approaches.

Contribution

It extends EFT methods to the reheating phase, introduces a new EFT framework accounting for oscillations and symmetry breaking, and proposes novel reheating models with observational predictions.

Findings

Established conditions for inflaton decay and resonance.

Developed a new EFT framework for reheating with hierarchical scales.

Predicted gravitational wave signatures from new reheating models.

Abstract

We investigate whether Effective Field Theory (EFT) approaches, which have been useful in examining inflation and dark energy, can also be used to establish a systematic approach to inflationary reheating. We consider two methods. First, we extend Weinberg's background EFT to the end of inflation and reheating. We establish when parametric resonance and decay of the inflaton occurs, but also find intrinsic theoretical limitations, which make it difficult to capture some reheating models. This motivates us to next consider Cheung, et. al.'s EFT approach, which instead focuses on perturbations and the symmetry breaking induced by the cosmological background. Adapting the latter approach to reheating implies some new and important differences compared to the EFT of Inflation. In particular, there are new hierarchical scales, and we must account for inflaton oscillations during reheating, which lead to discrete symmetry breaking. Guided by the fundamental symmetries, we construct the EFT of reheating, and as an example of its usefulness we establish a new class of reheating models and the corresponding predictions for gravity wave observations. In this paper we primarily focus on the first stages of preheating. We conclude by discussing challenges for the approach and future directions. This paper builds on ideas first proposed in the note arXiv:1507.06651.