Constraining self-interacting fermionic dark matter in admixed neutron stars using multimessenger astronomy

Understand

We investigate the structure of admixed neutron stars with a regular hadronic component and a fraction of fermionic self-interacting dark matter.

• Using two limiting equations of state for the dense baryonic interior, constructed from piecewise generalised polytropes, and an asymmetric self-interacting fermionic dark component, we analyse different scenarios of admixed neutron stars depending on the mass of dark fermions $m_\chi$, interaction mediators $m_\phi$, and self-interacting strengths $g$.
• We find that the contribution of dark matter to the masses and radii of neutron stars leads to tension with mass estimates of the pulsar J0453+1559, the least massive neutron star, and with the constraints coming from the GW170817 event.
• We discuss the possibilities of constraining dark matter model parameters $g$ and $y \equiv m_\chi/m_\phi$, using current existing knowledge on neutron star estimations of mass, radius, and tidal deformability, along with the accepted cosmological dark matter freeze-out values and self-interaction cross-section to mass ratio, $\sigma_\mathrm{SI}/m_\chi$, fitted to explain Bullet, Abell, and dwarf galaxy cluster dynamics.