Late-time creation of gravitinos from the vacuum

TL;DR

This paper investigates the ongoing creation of gravitinos after inflation, showing that they can be produced continuously until a later epoch, which has significant implications for cosmological models and the need for thermal inflation.

Contribution

It demonstrates that gravitino creation persists at late times after inflation, extending previous understanding and using recent theoretical descriptions of helicity 1/2 gravitinos.

Findings

Late-time gravitino creation maintains a constant number density.

Such gravitinos are abundant in typical inflation models.

Thermal inflation is required to dilute late-time gravitinos.

Abstract

Starting with the vacuum fluctuation, it is known that gravitinos will be created just after inflation, with number density $\sim 10^{-2}M^3$ where $M$ is the mass of the inflaton. Here, we argue that creation may be expected to continue, maintaining about the same number density, until a usually much later epoch. This epoch is either the `intermediate epoch' when Hubble parameter falls below the gravitino mass, or the reheat epoch if that is earlier. We verify that such late-time creation indeed occurs if only a single chiral superfield is relevant, using the description of the helicity 1/2 gravitino provided recently by Kallosh et. al. (hep-th/9907124) and Giudice et. al. (hep-ph/9907510). Arguments are presented in favor of late-time creation in the general case. For the usual inflation models, $M$ is rather large and gravitinos from late-time creation are so abundant that a subsequent era of thermal inflation is needed to dilute them.