@article{froustey_richers_grohs_flynn_foucart_kneller_mclaughlin_2024, title={Neutrino fast flavor oscillations with moments: Linear stability analysis and application to neutron star mergers}, volume={109}, ISSN={["2470-0029"]}, url={https://www.osti.gov/biblio/2311835}, DOI={10.1103/PhysRevD.109.043046}, abstractNote={Providing an accurate modeling of neutrino physics in dense astrophysical environments such as binary neutron star mergers presents a challenge for hydrodynamic simulations. Nevertheless, understanding how flavor transformation can occur and affect the dynamics, the mass ejection, and the nucleosynthesis will need to be achieved in the future. Computationally expensive, large-scale simulations frequently evolve the first classical angular moments of the neutrino distributions. By promoting these quantities to matrices in flavor space, we develop a linear stability analysis of fast flavor oscillations using only the first two ``quantum'' moments, which notably requires generalizing the classical closure relations that appropriately truncate the hierarchy of moment equations in order to treat quantum flavor coherence. After showing the efficiency of this method on a well-understood test situation, we perform a systematic search of the occurrence of fast flavor instabilities in a neutron star merger simulation. We discuss the successes and shortcomings of moment linear stability analysis, as this framework provides a time-efficient way to design and study better closure prescriptions in the future.}, number={4}, journal={PHYSICAL REVIEW D}, author={Froustey, Julien and Richers, Sherwood and Grohs, Evan and Flynn, Samuel D. and Foucart, Francois and Kneller, James P. and McLaughlin, Gail C.}, year={2024}, month={Feb} }
 @article{grohs_richers_couch_foucart_froustey_kneller_mclaughlin_2024, title={Two-moment Neutrino Flavor Transformation with Applications to the Fast Flavor Instability in Neutron Star Mergers}, volume={963}, ISSN={["1538-4357"]}, url={https://www.osti.gov/biblio/2310431}, DOI={10.3847/1538-4357/ad13f2}, abstractNote={Abstract
               Multi-messenger astrophysics has produced a wealth of data with much more to come in the future. This enormous data set will reveal new insights into the physics of core-collapse supernovae, neutron star mergers, and many other objects where it is actually possible, if not probable, that new physics is in operation. To tease out different possibilities, we will need to analyze signals from photons, neutrinos, gravitational waves, and chemical elements. This task is made all the more difficult when it is necessary to evolve the neutrino component of the radiation field and associated quantum-mechanical property of flavor in order to model the astrophysical system of interest—a numerical challenge that has not been addressed to this day. In this work, we take a step in this direction by adopting the technique of angular-integrated moments with a truncated tower of dynamical equations and a closure, convolving the flavor-transformation with spatial transport to evolve the neutrino radiation quantum field. We show that moments capture the dynamical features of fast flavor instabilities in a variety of systems, although our technique is by no means a universal blueprint for solving fast flavor transformation. To evaluate the effectiveness of our moment results, we compare to a more precise particle-in-cell method. Based on our results, we propose areas for improvement and application to complementary techniques in the future.}, number={1}, journal={ASTROPHYSICAL JOURNAL}, author={Grohs, Evan and Richers, Sherwood and Couch, Sean M. and Foucart, Francois and Froustey, Julien and Kneller, James P. and McLaughlin, Gail C.}, year={2024}, month={Mar} }