Cosmological constraints on the gravitino LSP scenario with a sneutrino NLSP

We study the scenario where a sneutrino is the next to lightest supersymmetric particle (NLSP) which decays into a gravitino and standard model particles. The daughter particles such as neutrinos and quarks cause electromagnetic and hadronic showers and affect big-bang nucleosynthesis. It is found that, despite a small branching ratio, four-body processes including quarks in the final state give the most stringent constraint on the sneutrino abundance for gravitino mass of 1–100 GeV. Pion production by high-energy neutrinos is important when the sneutrinos decay at $\sim 1\sec$. We also discuss the thermal leptogenesis in the sneutrino NLSP scenario.