Abstract
In this work, we explore the ``degenerate gravitino'' scenario where the mass difference between the gravitino and the lightest MSSM particle is much smallerthan the gravitino mass itself. In this case, the energy released in the decay of thenext to lightest sypersymmetric particle (NLSP) is reduced. Consequently the cosmological and astrophysical constraints on the gravitino abundance, and hence on the reheating temperature, become softer than in the usual case. On the other hand, such small mass splittings generically imply a much longer lifetime for the NLSP. We find that, in the constrained MSSM (CMSSM), for neutralino LSP or NLSP, reheating temperatures compatible with thermal leptogenesis are reached for small splittings of order 10−2 GeV. While for stau NLSP, temperatures of TRH ≃ 4 × 109GeV can be obtained even for splittings of order of tens of GeVs. This ``degenerate gravitino'' scenario offers a possible way out to the gravitino problem for thermal leptogenesis in supersymmetric theories.
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