Non-thermal Gravitino Production in Tribrid Inflation

TL;DR

This paper shows that tribrid inflation models in supergravity naturally suppress non-thermal gravitino production, avoiding the severe constraints faced by traditional hybrid inflation models, due to specific decay dynamics of involved fields.

Contribution

It demonstrates that tribrid inflation inherently avoids the non-thermal gravitino problem through decay channel differences and decay timing, a novel insight compared to previous models.

Findings

Waterfall field decay dominates over gravitino production

Inflaton decay occurs later, diluting gravitino abundance

Non-thermal gravitino problem is generally absent in tribrid inflation

Abstract

We investigate non-thermal gravitino production after tribrid inflation in supergravity, which is a variant of supersymmetric hybrid inflation where three fields are involved in the inflationary model and where the inflaton field resides in the matter sector of the theory. In contrast to conventional supersymmetric hybrid inflation, where non-thermal gravitino production imposes severe constraints on the inflationary model, we find that the "non-thermal gravitino problem" is generically absent in models of tribrid inflation, mainly due to two effects: (i) With the inflaton in tribrid inflation (after inflation) being lighter than the waterfall field, the latter has a second decay channel with a much larger rate than for the decay into gravitinos. This reduces the branching ratio for the decay of the waterfall field into gravitinos. (ii) The inflaton generically decays later than the waterfall field, and does not produce gravitinos when it decays. This leads to a dilution of the gravitino population from the decays of the waterfall field. The combination of both effects generically leads to a strongly reduced gravitino production in tribrid inflation.