Bound-state effects on light-element abundances in gravitino dark matter scenarios

Abstract

If the gravitino is the lightest supersymmetric particle and the long-lived next-to-lightest sparticle (NSP) is the stau, the charged partner of the tau lepton, it may be metastable and form bound states with several nuclei. These bound states may affect the cosmological abundances of 6 Li and 7 Li by enhancing nuclear rates that would otherwise be strongly suppressed. We consider the effects of these enhanced rates on the final abundances produced in Big-Bang nucleosynthesis (BBN), including injections of both electromagnetic and hadronic energy during and after BBN. We calculate the dominant two-and three-body decays of both neutralino and stau NSPs, and model the electromagnetic and hadronic decay products using the PYTHIA event generator and a cascade equation. Generically, the introduction of bound states drives light element abundances further from their observed values; however, for small regions of parameter space bound state effects can bring lithium abundances in particular in better accord with observations. We show that in regions where the stau is the NSP with a lifetime longer than 10 3 − 10 4 s, the abundances of 6 Li and 7 Li are far in excess of those allowed by observations. For shorter lifetimes of order 1000 s, we comment on the possibility in minimal supersymmetric and supergravity models that stau decays could reduce the 7 Li abundance from standard BBN values while at the same time enhancing the 6 Li abundance.

Probing the reheating temperature at colliders and with primordial nucleosynthesis

“…It is the region to the right of the respective line that is disfavored by 6 Li/H| CBBN exceeding the limit inferred from observations. Only the constraint from the primordial D abundance on hadronic energy release [4,6] in l 1 decays [20,21,22] can be more severe than the CBBN constraints [7,15,23,43,44,46]. 10 In Figs.…”

“…In the considered gravitino LSP scenarios, this bound applies directly to the lifetime of the l 1 NLSP [7,15,23,42,43,44,45,46,47,48]: τ e l1 5 × 10 3 s. 2 This implies m e G 0.1 m e l1 in the colliderfriendly mass range of m e l1 1 TeV. Accordingly, the region 0.1 m e l1 m e G < m e l1 , in which the kinematical m e G determination appears feasible, seems to be excluded by BBN constraints [44].…”

Structure of dark matter halos in warm dark matter models and in models with long-lived charged massive particles

“…For example, the stau can be the next lightest supersymmetric particle (NLSP) when the gravitino is the LSP (Buchmüller et al 2006). It is well-known that CHAMPs could affect the big bang nucleosynthesis (BBN) reaction rates and thus change the abundance of light elements (Pospelov 2007;Kohri & Takayama 2007;Kaplinghat & Rajaraman 2006;Cyburt et al 2006;Steffen 2007;Hamaguchi et al 2007;Kawasaki et al 2007;Jedamzik 2008a,b;Jittoh et al 2011). Several authors (Sigurdson & Kamionkowski 2004;Kohri & Takahashi 2010) suggest the possibility that CHAMPs with a lifetime about 1 yr can act effectively as WDM through acoustic oscillations in the thermal background.…”

Thermal relic abundances of long-lived staus

“…Indeed, to decide on the cosmological viability of a SUSY model, one has to confront the associated Y e τ values with those constraints. In particular, for gravitino LSP scenarios with unbroken R-parity, restrictive cosmological constraints and implications thereof have been derived [48,39,40,41,57,42,32,93,36] often under the assumption that Y e τ can be described by (1.1). However, while (1.1) is quite reliable for τ 1 ≃ τ R [37,38,40,52], we have shown in the previous sections that Y e τ (for a given m e τ 1 ) can be about than two orders of magnitude smaller than (1.1).…”

“…(iii) The τ e τ 1 limit can point to a CMSSM mass spectrum which will be difficult to probe at the Large Hadron Collider (LHC) [48,40,41,42]. Indeed, the τ e τ 1 limit can be relaxed only with a significant reduction of (1.1) which has been presented explicitly so far only for non-standard cosmological scenarios with a very low value of T R [49] or with late-time entropy production after τ 1 decoupling and before BBN [40,50].…”