Astrophysical constraints on dark-matter $Q$-balls in the presence of baryon-violating operators

Abstract

Supersymmetric extensions of the standard model predict the existence of non-topological solitons, $Q$-balls. Assuming the standard cosmological history preceded by inflation, $Q$-balls can form in the early universe and can make up the dark matter. The relatively large masses of such dark-matter particles imply a low number density, making direct detection very challenging. The strongest limits come from the existence of neutron stars because, if a baryonic $Q$-ball is captured by a neutron star, the $Q$-ball can absorb the baryon number releasing energy and eventually destroying a neutron star. However, in the presence of baryon number violating higher-dimension operators, the growth of a $Q$-ball inside a neutron star is hampered once the $Q$-ball reaches a certain size. We re-examine the limits and identify some classes of higher-dimensional operators for which supersymmetric $Q$-balls can account for dark matter. The present limits leave a wide range of parameters available for dark matter in the form of supersymmetric $Q$-balls.