Reheating the Universe After Multi-Field Inflation

TL;DR

This paper investigates the reheating process after multi-field inflation, focusing on the efficiency of parametric resonance and perturbative decay, and introduces a mathematical framework for analyzing multi-field preheating dynamics.

Contribution

It provides a detailed analysis of reheating mechanisms in multi-field inflation, including the development of a multi-field Floquet theory and insights into scalar and gauge field production.

Findings

Quartic couplings lead to inefficient parametric resonance in multi-field scenarios.

Trilinear couplings enable strong nonperturbative preheating via tachyonic resonance.

Perturbative decay can fully reheat the universe with trilinear interactions.

Abstract

We study in detail (p)reheating after multi-field inflation models with a particular focus on N-flation. We consider a variety of different couplings between the inflatons and the matter sector, including both quartic and trilinear interactions with a light scalar field. We show that the presence of multiple oscillating inflatons makes parametric resonance inefficient in the case of the quartic interactions. Moreover, perturbative processes do not permit a complete decay of the inflaton for this coupling. In order to recover the hot big bang, we must instead consider trilinear couplings. In this case we show that strong nonperturbative preheating is possible via multi-field tachyonic resonance. In addition, late-time perturbative effects do permit a complete decay of the condensate. We also study the production of gauge fields for several prototype couplings, finding similar results to the trilinear scalar coupling. During the course of our analysis we develop the mathematical theory of the quasi-periodic Mathieu equation, the multi-field generalization of the Floquet theory familiar from preheating after single field inflation. We also elaborate on the theory of perturbative decays of a classical inflaton condensate, which is applicable in single-field models also.