Constraining bosonic asymmetric dark matter with neutron star mass-radius measurements

Abstract

Neutron stars can accumulate asymmetric dark matter (ADM) in their interiors, which affects the neutron star's measurable properties and makes compact objects prime targets to search for ADM. In this work, we use Bayesian inference to explore potential neutron star mass-radius measurements, from current and future x-ray telescopes, to constrain the bosonic ADM parameters for the case where bosonic ADM has accumulated in the neutron star interior. We find that the current uncertainties in the baryonic equation of state do not allow for constraints on the ADM parameter space to be made. However, we also find that ADM cannot be excluded and the inclusion of bosonic ADM in neutron star cores relaxes the constraints on the baryonic equation of state space. If the baryonic equation of state were more tightly constrained independent of ADM, we find that statements about the ADM parameter space could be made. In particular, we find that the high bosonic ADM particle mass ($m_\chi$) and low effective self-interaction strength ($g_\chi/m_\phi)$ regime is disfavored due to the observationally and theoretically motivated constraint that neutron stars must have at least a mass of $1 \, \mathrm{M_\odot}$. However, within the remaining parameter space, $m_\chi$ and $g_\chi/m_\phi$ are individually unconstrained. On the other hand, the ADM mass-fraction, i.e., the fraction of ADM mass inside the neutron star, can be constrained by such neutron star measurements.