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, delta m, must satisfy delta m/m((chi) over tilde)similar to a few % or less for coannihilation to occur, where m((chi) over tilde) is the neutralino mass. We calculate the stau lifetime from the decay modes (tau) over tilde ->(chi) over tilde tau, (chi) over tilde nu(tau)pi, and (chi) over tilde nu(tau)mu(e)nu(mu(e)) and discuss its dependence on various parameters. We find that the lifetime is in the range 10(-22)-10(16) sec for 10(-2) <= delta m <= 10 GeV. We also discuss the connection with lepton flavor violation if there is mixing between sleptons.