Investigating the influence of the full-kinematics treatment for charged-current processes in binary neutron star mergers

RESUMO

Weak interactions are fundamental in the merger of binary neutron stars (BNS). They provide cooling, change the composition of matter outflows, and can lead to significant secular outflows through neutrino-driven winds. Hence, the inclusion of neutrino transport has become standard in numerical-relativity simulations of mergers involving neutron stars. In more detail, the interactions of neutrinos with matter in a truncated two-moments scheme (M1) are described through interaction rates, calculated from a set of standard interactions. Among those are charged-current reactions, for which the elastic approximation is commonly assumed. More sophisticated alternatives are provided by, e.g., the publicly available NuLib library, or rates computed within a full kinematics approach. In this work, we compare merger simulations of a BNS systems employing each of these three prescriptions for the computation of charged-current weak rates, included in the M1 equations with an implicit-explicit time integrator. We find that the elastic approximation slightly overestimates the dynamical ejecta mass, while underestimating the amount of high electron fraction material therein. Additionally, it overestimates the neutrino luminosities at early times. The effects of full kinematics in comparison to the NuLib rates appear negligible within the uncertainties of the simulation data. Similarly, the post-merger gravitational-wave spectra for the three prescriptions were found to be indistinguishable within the numerical uncertainties. Nucleosynthetic yields, computed with a nuclear network, are broadly consistent, except in the atomic mass range $A\in[90,125]$ where the elastic approximation shows larger abundances. Finally, the different interaction rates seem to affect the remnant disk properties, hinting at the importance of more accurate interaction rates for simulations spanning secular timescales.