Gravitino dark matter in the CMSSM and implications for leptogenesis and the LHC

Abstract

In the framework of the CMSSM we study the gravitino as the lightest supersymmetric particle and the dominant component of cold dark matter in the Universe. We include both a thermal contribution to its relic abundance from scatterings in the plasma and a non-thermal one from neutralino or stau decays after freeze-out. In general both contributions can be important, although in different regions of the parameter space. We further include constraints from BBN on electromagnetic and hadronic showers, from the CMB blackbody spectrum and from collider and non-collider SUSY searches. The region where the neutralino is the next-to-lightest superpartner is severely constrained by a conservative bound from excessive electromagnetic showers and probably basically excluded by the bound from hadronic showers, while the stau case remains mostly allowed. In both regions the constraint from CMB is often important or even dominant. In the stau case, for the assumed reasonable ranges of soft SUSY breaking parameters, we find regions where the gravitino abundance is in agreement with the range inferred from CMB studies, provided that, in many cases, a reheating temperature T R is large, T R ∼ 10 9 GeV. On the other side, we find an upper bound T R ∼ < 5 × 10 9 GeV. Less conservative bounds from BBN or an improvement in measuring the CMB spectrum would provide a dramatic squeeze on the whole scenario, in particular it would strongly disfavor the largest values of T R ∼ 10 9 GeV. The regions favored by the gravitino dark matter scenario are very different from standard regions corresponding to the neutralino dark matter, and will be partly probed at the LHC.

Gravitino dark matter and cosmological constraints

“…Therefore, the hadronic nucleosynthesis constraints given in Refs. [21,22,23], which were derived from the simplified estimate of Ref. [21], have to be updated.…”

“…In other words, the hadronic branching ratio was significantly underestimated in Refs. [21,22,23] towards smaller values of mτ , where the photon exchange gives the dominant contribution.…”

“…In addition to the limits from the properties of dark matter, there are also constraints from the observed abundances of the primordial light elements (D, He, Li) [20,21,22,23]. Because of the extremely weak interactions of the gravitino, the NLSP typically has a long lifetime before it decays into the gravitino.…”

“…While most of the existing investigations focus on the effects of electromagnetic energy injection (see [20,30,31] and references therein), the bounds from hadronic energy injection can be much more severe [28,29,32,33,34,35]. In particular, the hadronic constraints strongly restrict the mass spectrum in the bino-like neutralino NLSP case [22,23]. For the slepton NLSP case, the hadronic constraints have also been estimated and found to be much weaker but still significant in much of the parameter space [21,22,23].…”

“…In particular, the hadronic constraints strongly restrict the mass spectrum in the bino-like neutralino NLSP case [22,23]. For the slepton NLSP case, the hadronic constraints have also been estimated and found to be much weaker but still significant in much of the parameter space [21,22,23].…”