Gravitino Decay in High Scale Supersymmetry with R-parity Violation

TL;DR

This paper investigates how R-parity violation affects gravitino decay in high scale supersymmetry, deriving bounds on the violation parameter and predicting potential neutrino signals detectable by IceCube.

Contribution

It provides new bounds on R-parity violation in high scale SUSY with EeV gravitino dark matter, linking decay channels to neutrino observables.

Findings

Gravitino lifetime constrains R-parity violation to below 50 keV.

Decay channels produce EeV neutrinos detectable by IceCube.

Potential for mono-chromatic neutrino flux at EeV energies.

Abstract

We consider the effects of R-parity violation due to the inclusion of a bilinear $\mu^\prime L H_u$ superpotential term in high scale supersymmetric models with an EeV scale gravitino as dark matter. Although the typical phenomenological limits on this coupling (e.g. due to lepton number violation and the preservation of the baryon asymmetry) are relaxed when the supersymmetric mass spectrum is assumed to be heavy (in excess of the inflationary scale of $3 \times 10^{13}$ GeV), the requirement that the gravitino be sufficiently long-lived so as to account for the observed dark matter density, leads to a relatively strong bound on $\mu^\prime \lesssim 20$ GeV. The dominant decay channels for the longitudinal component of the gravitino are $Z \nu, W^\pm l^\mp$, and $h\nu$. To avoid an excess neutrino signal in IceCube, our limit on $\mu'$ is then strengthened to $\mu' \lesssim 50$ keV. When the bound is saturated, we find that there is a potentially detectable flux of mono-chromatic neutrinos with EeV energies.