Moduli Decays and Gravitinos

TL;DR

The paper tackles the moduli problem in string cosmology by analyzing heavy moduli decays to gravitinos through the lens of the Goldstino equivalence theorem. It shows that decays to gravitinos are highly model-dependent: in KKLT-like setups with a simple hidden sector, decays are suppressed by the gravitino mass $m_{3/2}$ due to supersymmetric mixing, but such suppression can be lifted by specific Kähler potential deformations or in more general hidden sectors where soft masses are large. These results illuminate how the SUSY-breaking structure and modulus-hidden sector mixing control gravitino production, with important cosmological implications for reheating, dark matter, and inflaton decays to gravitinos. The analysis suggests that viable cosmologies can exist with heavy moduli if gravitino production is adequately suppressed or if the gravitino mass is sufficiently large, though in some models the gravitino problem or a moduli problem can be revived depending on the microphysics.

Abstract

One proposed solution of the moduli problem of string cosmology requires that the moduli are quite heavy, their decays reheating the universe to temperatures above the scale of nucleosynthesis. In many of these scenarios, the moduli are approximately supersymmetric; it is then crucial that the decays to gravitinos are helicity suppressed. In this paper, we discuss situations where these decays are, and are not, suppressed. We also comment on a possible gravitino problem from inflaton decay.