Strange Quark Stars as Probe of Dark Matter

Abstract: We demonstrate that the observation of old strange quark stars (SQSs) can set important limits on the scattering cross sections $\sigma_q$ between the light quarks and the non-interacting scalar dark matter (DM). By analyzing a set of 1403 of solitary pulsarlike compact stars in the Milky Way, we find the old solitary pulsar PSR J1801-0857D can set the most stringent upper limits on $\sigma_q$ or the DM-proton scattering cross sections $\sigma_p$. By converting $\sigma_q$ into $\sigma_p$ based on effective operator analyses, we show the resulting $\sigma_p$ limit by assuming PSR J1801-0857D to be a SQS could be comparable with that of the current direct detection experiments but much weaker (by several orders of magnitude) than that obtained by assuming PSR J1801-0857D to be a neutron star (NS), which requires an extremely small $\sigma_p$ far beyond the limits of direct detection experiments. Our findings imply that the old pulsars are favored to be SQSs rather than NSs if the scalar DM were observed by future terrestrial experiments.