Implementation of Monte Carlo Transport in the General Relativistic SpEC Code

Neutrino transport and neutrino-matter interactions are known to play an important role in the evolution of neutron star mergers, their post-merger remnants. Neutrinos cool remnants, drive winds, deposit energy low-density polar regions where relativistic jets may eventually form. also modify composition ejected material, impacting outcome nucleosynthesis merger outflows properties optical/infrared transients that they power (kilonovae). So far, simulations have largely relied on approximate treatments neutrinos (leakage, moments) simplify equations radiation a way makes more affordable, but introduces unquantifiable errors results. To improve these methods, we recently published first simulation mergers using low-cost Monte-Carlo algorithm for neutrino transport. Our code limits costs optically thick by placing hard ceiling value absorption opacity fluid, yet all approximations made within designed vanish limit infinite numerical resolution. We provide here in-depth description this algorithm, its implementation SpEC code, expected impact our regions. argue latter is subdominant source error at accuracy reached current simulations, currently included code. tests most features