Dark Matter or Regular Matter in Neutron Stars? How to tell the difference from the coalescence of compact objects

Understand

The mirror twin Higgs model is a candidate for (strongly-interacting) complex dark matter, which mirrors SM interactions with heavier quark masses.

• A consequence of this model are mirror neutron stars -- exotic stars made entirely of mirror matter, which are significantly smaller than neutron stars and electromagnetically dark.
• This makes mergers of two mirror neutron stars detectable and distinguishable in gravitational wave observations, but can we observationally distinguish between regular neutron stars and those that may contain some mirror matter? This is the question we study in this paper, focusing on two possible realizations of mirror matter coupled to standard model matter within a compact object: (i) mirror matter captured by a neutron star and (ii) mirror neutron star-neutron star coalescences.
• Regarding (i), we find that (non-rotating) mirror-matter-admixed neutron stars no longer have a single mass-radius sequence, but rather exist in a two-dimensional mass-radius plane.