@article{deaton_o'connor_zhu_bohn_jesse_foucart_duez_mclaughlin_2018, title={Elastic scattering in general relativistic ray tracing for neutrinos}, volume={98}, ISSN={["2470-0029"]}, DOI={10.1103/PhysRevD.98.103014}, abstractNote={We present a covariant ray tracing algorithm for computing high-resolution neutrino distributions in general relativistic numerical spacetimes with hydrodynamical sources. Our formulation treats the very important effect of elastic scattering of neutrinos off of nuclei and nucleons (changing the neutrino's direction but not energy) by incorporating estimates of the background neutrino fields. Background fields provide information about the spectra and intensities of the neutrinos scattered into each ray. These background fields may be taken from a low-order moment simulation or be ignored, in which case the method reduces to a standard state-of-the-art ray tracing formulation. The method handles radiation in regimes spanning optically thick to optically thin. We test the new code, highlight its strengths and weaknesses, and apply it to a simulation of a neutron star merger to compute neutrino fluxes and spectra, and to demonstrate a neutrino flavor oscillation calculation. In that environment, we find qualitatively different fluxes, spectra, and oscillation behaviors when elastic scattering is included.}, number={10}, journal={PHYSICAL REVIEW D}, author={Deaton, M. Brett and O'Connor, Evan and Zhu, Y. L. and Bohn, Andy and Jesse, Jerred and Foucart, Francois and Duez, Matthew D. and McLaughlin, G. C.}, year={2018}, month={Nov} }
 @article{nouri_duez_foucart_deaton_haas_haddadi_kidder_ott_pfeiffer_scheel_et al._2018, title={Evolution of the magnetized, neutrino-cooled accretion disk in the aftermath of a black hole-neutron star binary merger}, volume={97}, ISSN={["2470-0029"]}, DOI={10.1103/physrevd.97.083014}, abstractNote={Black hole--torus systems from compact binary mergers are possible engines for gamma-ray bursts (GRBs). During the early evolution of the postmerger remnant, the state of the torus is determined by a combination of neutrino cooling and magnetically driven heating processes, so realistic models must include both effects. In this paper, we study the postmerger evolution of a magnetized black hole--neutron star binary system using the Spectral Einstein Code (SpEC) from an initial postmerger state provided by previous numerical relativity simulations. We use a finite-temperature nuclear equation of state and incorporate neutrino effects in a leakage approximation. To achieve the needed accuracy, we introduce improvements to SpEC's implementation of general-relativistic magnetohydrodynamics (MHD), including the use of cubed-sphere multipatch grids and an improved method for dealing with supersonic accretion flows where primitive variable recovery is difficult. We find that a seed magnetic field triggers a sustained source of heating, but its thermal effects are largely cancelled by the accretion and spreading of the torus from MHD-related angular momentum transport. The neutrino luminosity peaks at the start of the simulation, and then drops significantly over the first 20 ms but in roughly the same way for magnetized and nonmagnetized disks. The heating rate and disk's luminosity decrease much more slowly thereafter. These features of the evolution are insensitive to grid structure and resolution, formulation of the MHD equations, and seed field strength, although turbulent effects are not fully converged.}, number={8}, journal={PHYSICAL REVIEW D}, author={Nouri, Fatemeh Hossein and Duez, Matthew D. and Foucart, Francois and Deaton, M. Brett and Haas, Roland and Haddadi, Milad and Kidder, Lawrence E. and Ott, Christian D. and Pfeiffer, Harald P. and Scheel, Mark A. and et al.}, year={2018}, month={Apr} }