Gravitino Dark Matter and Cosmological Constraints

The gravitino is a promising candidate for cold dark matter. We study cosmological constraints on scenarios in which the gravitino is the lightest supersymmetric particle and a charged slepton the next-to-lightest supersymmetric particle (NLSP). We obtain new results for the hadronic nucleosynthesis bounds by computing the 4-body decay of the NLSP slepton into the gravitino, the associated lepton, and a quark-antiquark pair. The bounds from the observed dark matter density are refined by taking into account gravitinos from both late NLSP decays and thermal scattering in the early Universe. We examine the present free-streaming velocity of gravitino dark matter and the limits from observations and simulations of cosmic structures. Assuming that the NLSP sleptons freeze out with a thermal abundance before their decay, we derive new bounds on the slepton and gravitino masses. The implications of the constraints for cosmology and collider phenomenology are discussed and the potential insights from future experiments are outlined. We propose a set of benchmark scenarios with gravitino dark matter and long-lived charged NLSP sleptons and describe prospects for the Large Hadron Collider and the International Linear Collider.Comment: 51 pages, 20 figures, revised version matches published version (results unchanged, JHEP style used, figures replaced with new high-quality figures, typos corrected, references added

Axino dark matter from thermal production

The axino is a promising candidate for dark matter in the Universe. It is electrically and color neutral, very weakly interacting, and could be - as assumed in this study - the lightest supersymmetric particle, which is stable for unbroken R-parity. In supersymmetric extensions of the standard model, in which the strong CP problem is solved via the Peccei-Quinn mechanism, the axino arises naturally as the fermionic superpartner of the axion. We compute the thermal production rate of axinos in supersymmetric QCD. Using hard thermal loop resummation, we obtain a finite result in a gauge-invariant way, which takes into account Debye screening in the hot quark-gluon-squark-gluino plasma. The relic axino abundance from thermal scatterings after inflation is evaluated. We find that thermally produced axinos could provide the dominant part of cold dark matter, for example, for an axino mass of 100 keV and a reheating temperature of 10^6 GeV.Comment: 33 pages, 7 figures, 1 table, erratum adde

A note on the primordial abundance of stau NLSPs

In scenarios with a gravitino LSP, there exist strong BBN constraints on the abundance of a possible stau NLSP. We find that in settings with substantial left-right mixing of the stau mass eigenstates these constraints can be evaded even for very long-lived staus.Comment: 17 pages, 5 figures, discussion on vacuum stability adde

Supergravity at colliders

We consider supersymmetric theories where the gravitino is the lightest superparticle (LSP). Assuming that the long-lived next-to-lightest superparticle (NSP) is a charged slepton, we investigate two complementary ways to prove the existence of supergravity in nature. The first is based on the NSP lifetime which in supergravity depends only on the Planck scale and the NSP and gravitino masses. With the gravitino mass inferred from kinematics, the measurement of the NSP lifetime will test an unequivocal prediction of supergravity. The second way makes use of the 3-body NSP decay. The angular and energy distributions and the polarizations of the final state photon and lepton carry the information on the spin of the gravitino and on its couplings to matter and radiation. © 2004 Elsevier B.V. All rights reserved