When Does the Inflaton Decay?

TL;DR

This paper investigates whether the inflaton decays into radiation during inflation by calculating decay amplitudes and their effects, concluding that decay during inflation is generally negligible for typical parameters.

Contribution

It provides a detailed calculation of inflaton decay amplitudes during inflation and clarifies conditions under which decay can be considered negligible.

Findings

Decay amplitudes grow exponentially with e-folds but cancellations limit impact

Inflaton decay during inflation is negligible unless e-folds are extremely large

For typical parameters, inflaton decay occurs after inflation, not during

Abstract

In order for the inflaton to decay into radiation at the end of inflation, it needs to couple to light matter fields. In this article we determine whether such couplings cause the inflaton to decay during inflation rather than after it. We calculate decay amplitudes during inflation, and determine to what extent such processes have an impact on the mean and variance of the inflaton, as well as on the expected energy density of its decay products. Although the exponential growth of the decay amplitudes with the number of e-folds appears to indicate the rapid decay of the inflaton, cancellations among different amplitudes and probabilities result in corrections to the different expectation values that only grow substantially when the number of e-folds is much larger than the inverse squared inflaton mass in units of the Hubble scale. Otherwise, for typical parameter choices, it is safe to assume that the inflaton does not decay during inflation.