Gravitino dark matter and cosmological constraints

Abstract

The gravitino is a promising cold dark matter candidate. We study cosmological constraintson scenarios in which the gravitino is the lightest supersymmetric particle and a chargedslepton the next-to-lightest supersymmetric particle (NLSP). We obtain new results for thehadronic nucleosynthesis bounds by computing the four-body decay of the NLSP sleptoninto the gravitino, the associated lepton, and a quark–antiquark pair. The bounds fromthe observed dark matter density are refined by taking into account gravitinosfrom both late NLSP decays and thermal scattering in the early Universe. Weexamine the present free-streaming velocity of gravitino dark matter and the limitsfrom observations and simulations of cosmic structures. Assuming that the NLSPsleptons freeze out with a thermal abundance before their decay, we derive newbounds on the slepton and gravitino masses. The implications of the constraints forcosmology and collider phenomenology are discussed and the potential insightsfrom future experiments are outlined. We propose a set of benchmark scenarioswith gravitino dark matter and long-lived charged NLSP sleptons and describeprospects for the Large Hadron Collider and the International Linear Collider.