Conversion of baryonic fermions into squarks in neutron stars from supersymmetric dark matterQ-balls

Abstract

The gauge-mediated model of supersymmetry breaking implies that stable nontopological solitons, $Q$-balls, could form in the early Universe and comprise the dark matter. It is shown that the inclusion of the effects from gravity-mediation set an upper limit on the size of $Q$-balls. When in a dense baryonic environment $Q$-balls grow until reaching this limiting size at which point they fragment into two equal-sized $Q$-balls. This $Q$-splitting process will rapidly destroy a neutron star that absorbs even one $Q$-ball. The new limits on $Q$-ball dark matter require an ultralight gravitino ${m}_{3/2}\ensuremath{\lesssim}\mathrm{keV}$, naturally avoiding the gravitino overclosure problem, and providing the minimal supersymmetric standard model with a dark matter candidate where gravitino dark matter is not viable.