Effects of Mirror Dark Matter on Neutron-Star Structure and Tidal Deformability

Mirror dark matter (MDM) can modify neutron-star structure and tidal response through gravitational coupling. In this work, we construct an ordinary-matter equation of state (EOS) by comparing hadronic matter described by the relativistic mean-field NL3$\omega\rho$ model, and quark matter in the framework of the Nambu--Jona-Lasinio (NJL) model. The stable branch is determined through a Maxwell construction, which serves to connect distinct phases of matter. For the parameter sets considered here, $m_u=5.2~{\rm MeV}$ is the lowest light current-quark mass in the scanned range that satisfies the $2M_\odot$ maximum-mass requirement, while $m_u>5.2~{\rm MeV}$ all yield stable neutron-star configurations without a resolved macroscopic quark core. The small-radius inferences for PSR J0437--4715 and XTE J1814--338, together with the tidal-deformability constraint from GW170817, are sensitive to the dark-matter mass fraction $f_D$. The commonly used GW170817 interval $70\lesssim\Lambda_{1.4}\lesssim580$ corresponds approximately to $0.12\lesssim f_D\lesssim0.88$ in the present model. These results indicate that, even without a macroscopic quark core, MDM can provide an important mechanism for reducing the visible radius and modifying the tidal response of neutron stars.