Brane Cosmology and KK Gravitinos

TL;DR

This paper analyzes the cosmological implications of KK gravitinos in extra-dimensional models, concluding that their production conflicts with Big Bang Nucleosynthesis constraints, thus challenging certain non-standard expansion scenarios.

Contribution

It demonstrates that KK gravitino production is incompatible with non-standard expansion epochs after inflation in models with extra dimensions.

Findings

KK gravitino production violates BBN constraints

Reduced five-dimensional Planck mass must be very small

No viable M_5 value satisfies all cosmological constraints

Abstract

The cosmology of KK gravitinos in models with extra dimensions is considered. The main result is that the production of such KK modes is not compatible with an epoch of non--standard expansion after inflation. This is so because the BBN constraint on the zero mode forces the reduced five dimensional Planck mass $M_5$ down to values much smaller than the usual four dimensional one, but this in turn implies many KK states available for a given temperature. Once these states are taken into account one finds that there is no $M_5$ for which the produced KK gravitinos satisfy BBN and overclosure constraints. This conclusion holds for both flat and warped models in which only gravity propagates in the full spacetime.