New decay modes of gravitino dark matter

Abstract

We consider the three-body decays of gravitino dark matter in supersymmetric scenarios with bilinear $R$-parity violation. In particular, gravitino decays into $\ensuremath{\ell}{W}^{*}$ ($\ensuremath{\ell}f{\overline{f}}^{\ensuremath{'}}$) and $\ensuremath{\nu}{Z}^{*}$ ($\ensuremath{\nu}f\overline{f}$) are examined for gravitino masses below ${M}_{W}$. After computing the gravitino decay rates into these three-body final states and studying their dependence on supersymmetric parameters, we find that these new decay modes are often more important than the two-body decay, into a photon and a neutrino, considered in previous works. Consequently, the gravitino lifetime and its branching ratios are substantially modified, with important implications for the indirect detection of gravitino dark matter.