A Novel Solution to the Gravitino Problem

TL;DR

This paper proposes a new approach within string theory to address the gravitino overproduction problem in the early universe, using a brane-world scenario with non-linear supergravity.

Contribution

It introduces a novel mechanism involving anti-D3-branes and nilpotent superfields to evade the gravitino problem in supersymmetric cosmology.

Findings

Two distinct solutions to the gravitino problem are proposed.

The approach leads to different particle physics phenomenologies.

The model aligns with known dark matter density constraints.

Abstract

In a general phenomenological model with local supersymmetry, the amount of massive gravitinos produced in early universe tends to violate the known dark matter density bound by many orders of magnitude. In the brane world scenario in Type IIB string theory, we propose a novel way to evade this problem. There, the standard model of strong and electroweak interactions live inside the anti-${\rm D3}$-branes ($\overline{\rm D3}$-branes) that span the 3 large spatial dimensions. Here, the "potential" Goldstino to be absorbed by the gravitino (to become massive) is the fermion component of the open string nilpotent superfield $X$ (i.e., $X^2=0$) which is present only inside the $\overline{\rm D3}$-branes. This non-linear supergravity scenario offers 2 ways to solve the gravitino problem, with very different particle physics phenomenologies.