Long life stau in the minimal supersymmetric standard model

Abstract

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, $\ensuremath{\delta}m$, must satisfy $\ensuremath{\delta}m/{m}_{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}\ensuremath{\sim}$ a few % or less for coannihilation to occur, where ${m}_{\stackrel{\texttildelow{}}{\ensuremath{\chi}}}$ is the neutralino mass. We calculate the stau lifetime from the decay modes $\stackrel{\texttildelow{}}{\ensuremath{\tau}}\ensuremath{\rightarrow}\stackrel{\texttildelow{}}{\ensuremath{\chi}}\ensuremath{\tau}$, $\stackrel{\texttildelow{}}{\ensuremath{\chi}}{\ensuremath{\nu}}_{\ensuremath{\tau}}\ensuremath{\pi}$, and $\stackrel{\texttildelow{}}{\ensuremath{\chi}}{\ensuremath{\nu}}_{\ensuremath{\tau}}\ensuremath{\mu}(e){\ensuremath{\nu}}_{\ensuremath{\mu}(e)}$ and discuss its dependence on various parameters. We find that the lifetime is in the range ${10}^{\ensuremath{-}22}--{10}^{16}\text{ }\text{ }\mathrm{sec}$ for ${10}^{\ensuremath{-}2}\ensuremath{\le}\ensuremath{\delta}m\ensuremath{\le}10\text{ }\text{ }\mathrm{GeV}$. We also discuss the connection with lepton flavor violation if there is mixing between sleptons.