On the Feasibility of a Stop NLSP in Gravitino Dark Matter Scenarios

We analyze the possibility that the lighter stop t̃1 could be the next-to-lightest supersymmetric particle (NLSP) in models where the gravitino is the lightest supersymmetric particle (LSP). We do not find any possibility for a stop NLSP in the constrained MSSM with universal input soft supersymmetry-breaking masses at the GUT scale (CMSSM), but do find small allowed regions in models with non-universal Higgs masses (NUHM). We discuss the cosmological evolution of stop hadrons. Most t̃1qq ‘sbaryons’ and the corresponding ‘antisbaryons’ annihilate with conventional antibaryons and baryons into t̃1q̄ ‘mesinos’ and the corresponding ‘antimesinos’, respectively, shortly after the quark-hadron transition in the early Universe, and most mesinos and antimesinos subsequently annihilate. As a result, insufficient metastable charged stop hadrons survive to alter Big Bang nucleosynthesis. CERN-PH-TH/2007-003 January 2007 ∗ On sabbatical leave at: Facultad de Ciencias, Universidad de Colima, México.