Modulino Dark Matter and the INTEGRAL 511 keV Line

Abstract: In this paper we present a simple extension of the minimal supersymmetric standard model [MSSM] which "naturally" produces the INTEGRAL photon signal. The model can be embedded in an SU(5) grand unified theory [GUT] with gauge mediated SUSY breaking. The new ingredients are the addition of several MSSM singlets/moduli. While the masses of the singlets are at the weak scale, their mass splittings are suppressed by chiral symmetry breaking and naturally lie around an MeV. The decay of the heavier modulino to the lighter one with the associated production of electron - positron pairs explains the INTEGRAL signal. Finally, the detection of diffuse gamma rays from internal bremsstrahlung in the galactic halo would be a suggestive indication of dark matter decays associated with the 511 keV line, and is an unambiguous additional prediction of this model.