$\nu\texttt{bhlight}$: Radiation GRMHD for Neutrino-Driven Accretion Flows.

The 2017 detection of the in-spiral and merger of two neutron stars was a landmark discovery in astrophysics. We now know that such mergers are central engines of short gamma ray bursts and sites of r-process nucleosynthesis, where the heaviest elements in our universe are formed. In the coming years, we expect many more such mergers. Modeling such systems presents a significant computational challenge along with the observational one. To meet this challenge, we present $\nu\texttt{bhlight}$, a scheme for solving general relativistic magnetohydrodynamics with energy-dependent neutrino transport in full (3+1)-dimensions, facilitated by Monte Carlo methods. We present a suite of tests demonstrating the accuracy, efficacy, and necessity of our scheme. We demonstrate the potential of our scheme by running a sample calculation in a domain of interest---the dynamics and composition of the accretion disk formed by a binary neutron star merger.