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.