Gravitino Production After Inflation

TL;DR

This work addresses nonthermal gravitino production at the end of inflation in supergravity cosmology. By formulating phenomenological $N=1$ supergravity in an $SU(2,2|1)$ symmetric framework and introducing the conformon, the authors clarify the distinct conformal properties of gravitino helicity components and derive their time-dependent equations in FRW backgrounds. They show that helicity-1/2 gravitinos are not conformally suppressed and can be produced copiously during inflaton oscillations, while helicity-3/2 production remains gravitationally suppressed; the production is highly model-dependent and can violate cosmological bounds in simple single-field models. These results imply strong constraints on inflationary scenarios and motivate extending the analysis to multi-field setups and additional entropy production mechanisms to avoid gravitino overabundance.

Abstract

We investigate the production of gravitinos in a cosmological background. Gravitinos can be produced during preheating after inflation due to a combined effect of interactions with an oscillating inflaton field and absence of conformal invariance. In order to get insight on conformal properties of gravitino we reformulate phenomenological supergravity in SU(2,2|1)-symmetric way. The Planck mass and F- and D-terms appear via the gauge-fixed value of a superfield that we call conformon. We find that in general the probability of gravitino production is not suppressed by the small gravitational coupling. This may lead to a copious production of gravitinos after inflation. Efficiency of the new non-thermal mechanism of gravitino production is very sensitive to the choice of the underlying theory. This may put strong constraints on certain classes of inflationary models.