Influence of muons, pions, and trapped neutrinos on neutron star mergers

The merger of two neutron stars probes dense matter in a hot, neutrino-trapped regime. In this work, we investigate how fully accounting for pions ($\ensuremath{\pi}$), muons ($\ensuremath{\mu}$), and muon-type neutrinos (${\ensuremath{\nu}}_{\ensuremath{\mu}}$) in the trapped regime may affect the outcome of the merger. By performing fully general-relativistic hydrodynamics simulations of merging neutron stars with equations of state to which we systematically add those different particle species, we aim to provide a detailed assessment of the impact of muons and pions on the merger and postmerger phases. In particular, we investigate the merger thermodynamics, mass ejection, and gravitational wave emission. Our findings are consistent with previous expectations, that the inclusion of such microphysical degrees of freedom and finite temperature corrections leads to frequency shifts on the order of 100--200 Hz in the postmerger gravitational wave signal, relative to a fiducial cold nucleonic equation-of-state model.