Speaker
Description
Bulk viscosity in neutron stars plays an important role in the dynamics of binary neutron star mergers by damping density oscillations in the post-merger remnant. In this talk, I will review the computation of bulk viscosity in the warm, dense, neutrino-transparent cores of neutron stars for two possible compositions: nuclear matter and quark matter. For the nuclear matter equation of state (EoS), we employ relativistic density functional models with two representative parametrizations, DDME2 and NL3, which differ in the presence of the direct Urca threshold. For quark matter, we use the SU(3) Nambu–Jona-Lasinio (NJL) model extended by vector interactions and the ’t Hooft determinant term.
I will discuss the relevant weak-interaction processes in both nuclear and quark matter that give rise to bulk viscosity under merger conditions. I will then outline the derivation of the corresponding bulk viscosity coefficients and discuss the associated damping rates of density oscillations in binary neutron star mergers. Finally, I will address how bulk-viscous dynamics, potentially encoded in future observational data, may provide a probe of the microscopic composition and equation of state of neutron star interiors, including signatures associated with the onset of the direct Urca processes.