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, $δm$, must satisfy $δm/m_{\tildeχ} \sim$ a few % or less for coannihilation to occur, where $m_{\tildeχ}$ is the neutralino mass. We calculate the stau lifetime from the decay modes $\tildeτ\to \tildeχτ$, $\tildeχν_τπ$, and $\tildeχν_τμ(e)ν_{μ(e)}$ and discuss its dependence on various parameters. We find that the lifetime is in the range $10^{-22}$--$10^{16}$ sec for $10^{-2} \le δm \le 10$ GeV. We also discuss the connection with lepton flavor violation if there is mixing between sleptons.