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Abstract

Binary neutron star mergers play an important role in nuclear astrophysics:
their gravitational wave and electromagnetic signals carry information about
the equation of state of cold matter above nuclear saturation density, and they
may be one of the main sources of r-process elements in the Universe.
Neutrino-matter interactions during and after merger impact the properties of
these electromagnetic signals, and the relative abundances of the produced
r-process elements. Existing merger simulations are however limited in their
ability to realistically model neutrino transport and neutrino-matter
interactions. Here, we perform a comparison of the impact of the use of
state-of-the art two-moment or Monte-Carlo transport schemes on the outcome of
merger simulations, for a single binary neutron star system with a short-lived
neutron star remnant ($(5-10)\,{\rm ms}$). We also investigate the use of
different reaction rates in the simulations. While the best transport schemes
generally agree well on the qualitative impact of neutrinos on the system,
differences in the behavior of the high-density regions can significantly
impact the collapse time and the properties of the hot tidal arms in this
metastable merger remnant. The chosen interaction rates, transport algorithm,
as well as recent improvements by Radice et al to the two-moment algorithms can
all contribute to changes at the $(10-30)\%$ level in the global properties of
the merger remnant and outflows. The limitations of previous moment schemes
fixed by Radice et al also appear sufficient to explain the large difference
that we observed in the production of heavy-lepton neutrinos in a previous
comparison of Monte-Carlo and moment schemes in the context of a low mass
binary neutron star system.