Flat directions and gravitino production in SUSY models

TL;DR

This paper explores how large vacuum expectation values along flat directions in SUSY models can significantly enhance gravitino production after inflation, potentially conflicting with cosmological constraints unless the flat direction VEV is small.

Contribution

It highlights the impact of flat directions on gravitino production and identifies conditions under which the abundance exceeds cosmological bounds.

Findings

Enhanced gravitino production due to large gaugino masses

Potential conflict with cosmological bounds on gravitino abundance

Requirement for small initial flat direction VEVs to avoid overproduction

Abstract

Flat directions in supersymmetric models can get large vacuum expectation values in the early Universe which leads to a large mass for gauge bosons and gauginos. We point out that this can then result in enhanced gravitino production because the cross-section for the production of the +/- 1/2 helicity states of the gravitino is proportional to the square of the gaugino masses. We consider gravitino production after inflation in such a scenario and find that the abundance in some cases can be much larger than the upper bound on the gravtino abundance from cosmological constraints unless the flat direction field has a very small vacuum expectation value when it commences oscillating.