Opening the reheating box in multifield inflation

TL;DR

This paper develops a detailed formalism and numerical tools to accurately track the evolution of scalar fields and perturbations during reheating in multifield inflation, revealing significant impacts on non-adiabatic perturbations.

Contribution

It introduces a comprehensive framework and new analytical techniques for modeling reheating in multifield inflation, improving precision over standard approximations.

Findings

Ignoring reheating details can cause ~50% errors in perturbation amplitude estimates.

The new semi-analytic methods reduce errors to about 10%.

Numerical solutions are essential for accurate predictions in multifield inflation.

Abstract

The robustness of multi-field inflation to the physics of reheating is investigated. In order to carry out this study, reheating is described in detail by means of a formalism which tracks the evolution of scalar fields and perfect fluids in interaction (the inflatons and their decay products). This framework is then used to establish the general equations of motion of the background and perturbative quantities controlling the evolution of the system during reheating. Next, these equations are solved exactly by means of a new numerical code. Moreover, new analytical techniques, allowing us to interpret and approximate these solutions, are developed. As an illustration of a physical prediction that could be affected by the micro-physics of reheating, the amplitude of non-adiabatic perturbations in double inflation is considered. It is found that ignoring the fine-structure of reheating, as usually done in the standard approach, can lead to differences as big as $\sim 50\%$, while our semi-analytic estimates can reduce this error to $\sim 10\%$. We conclude that, in multi-field inflation, tracking the perturbations through the details of the reheating process is important and, to achieve good precision, requires the use of numerical calculations.