Long life stau in the minimal supersymmetric standard model

We study the stau lifetime in a scenario with the LSP taken to be a neutralino and the NLSP being a stau, based on the minimal supersymmetric Standard Model. The mass difference between the LSP and NLSP, δm, must satisfy δm/mχ-tilde∼ a few % or less for coannihilation to occur, where mχ-tilde is the neutralino mass. We calculate the stau lifetime from the decay modes τ-tilde→χ-tildeτ, χ-tildeντπ, and χ-tildeντμ(e)νμ(e) and discuss its dependence on various parameters. We find that the lifetime is in the range 10-22-1016 sec for 10-2≤δm≤10 GeV. We also discuss the connection with lepton flavor violation if there is mixing between sleptons