Implementation of Monte-Carlo radiation transport for the treatment of neutrinos in the SpEC merger code

Neutrino radiation transport plays an important role in the simulation of compact binary mergers involving neutron stars. Neutrinos are the main source of cooling of the post-merger remnant. Additionally, neutrino-matter interactions in the matter ejected during and after merger are crucial in determining the properties of the UV/optical/infrared transients following many neutron star mergers, as well as the outcome of nucleosynthesis in the ejecta. Properly evolving Boltzmann's equations for radiation transport remains however a difficult technical challenge. In this talk, I will review a significant step towards performing full transport in merger simulations: the implementation in the SpEC code of a Monte-Carlo algorithm. I will discuss the overall structure of a Monte-Carlo transport code, its advantages in the merger context, as well as the approximations that still have to be performed in order to keep simulations computationally affordable.