Predicting electromagnetic signals from binary neutron star mergers is a multi-scale, multi-physics problem. The only multi-messenger event detected so far from this type of system, GW170817, confirmed the basic physical picture of NS mergers, but the origin of its early blue emission and the nature of the GRB engine remains under debate. Moreover, throughout the next decade, more multi-messenger events will be observed, and thus better theoretical models will be crucial to interpret and identify them.
In this talk, I will present new GRMHD simulations of NS mergers which include neutrino transport and nuclear equations of state. I will first show a detailed analysis of the dynamical ejecta and its r-process nucleosynthesis obtained from these simulations. Based on these results and using new semi-analytical models, I will give a comprehensive picture of the electromagnetic signatures associated with the dynamical phase, namely, the free neutron precursor and the kilonova afterglow. Finally, I will show preliminary results on post-merger physics, where both magnetic fields and neutrinos become crucial to understanding the evolution and outflows from the system.