Superlight neutralino as a dark matter particle candidate

Abstract

We address the question of how light the lightest supersymmetric particle neutralino can be to be a reliable cold dark matter (CDM) particle candidate. To this end we perform a combined analysis of the parameter space of the minimal supersymmetric standard model (MSSM) taking into account cosmological and accelerator constraints including those from the radiative b\ensuremath{\rightarrow}s\ensuremath{\gamma} decay. Appropriate grand unification (GUT) scenarios are considered. We find that the relaxation of gaugino mass unification is sufficient to obtain a phenomenologically and cosmologically viable solution of the MSSM with a neutralino as light as 3 GeV. We find good prospects for the direct detection of these superlight CDM neutralinos via elastic scattering off various nuclei in the forthcoming experiments with low-threshold DM detectors. In a certain sense, these experiments can probe the gaugino mass unification giving constraints on the possible GUT scenarios within the MSSM.