Neutron Stars with a Stable, Light Supersymmetric Baryon

If a light gluino exists, the lightest gluino-containing baryon, the ${\rm S}^0$, is a possible candidate for self-interacting dark matter. In this scenario, the simplest explanation for the observed ratio $\Omega_{dm}/\Omega_b \approx 6-10$ is that $m_{S^0} \sim 900 $MeVc$^{-2}$; this is not at present excluded by particle physics. Such an ${\rm S}^0$ could be present in neutron stars, with hyperon formation serving as an intermediate stage. We calculate equilibrium compositions and equation of state for high density matter with ${\rm S}^0$, and find that for a wide range of parameters the properties of neutron stars with the ${\rm S}^0$ are consistent with observations. In particular, the maximum mass of a nonrotating star is $1.7-1.8 M_\odot$, and the presence of the ${\rm S}^0$ is helpful in reconciling observed cooling rates with hyperon formation.