Is gravitino still a warm dark matter candidate?

TL;DR

This paper assesses whether gravitinos can still be considered viable warm dark matter candidates by analyzing phase space density constraints and cosmological parameters, with implications for upcoming collider experiments.

Contribution

It provides a detailed phase space density analysis showing conditions under which gravitinos can be warm dark matter, considering cosmological and particle physics parameters.

Findings

Gravitinos with 1-15 keV mass can account for dark matter density.

Low reheat temperature (T_R  10 TeV) is necessary for viability.

LHC experiments can test the superparticle mass assumptions.

Abstract

We make use of the phase space density approach to discuss gravitino as a warm dark matter candidate. Barring fine tuning between the reheat temperature in the Universe and superparticle masses, we find that \emph{warm} gravitinos have both appropriate total mass density, Omega_{\tilde G} = \Omega_{DM} \simeq 0.2, and suitable primordial phase space density at low momenta provided that their mass is in the range 1 keV \lesssim \mg \lesssim 15 keV, the reheat temperature in the Universe is low, T_R \lesssim 10 TeV, and masses of some of the superparticles are sufficiently small, M \lesssim 350 GeV. The latter property implies that the gravitino warm dark matter scenario will be either ruled out or supported by the LHC experiments.