@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"]}, 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"]}, DOI={10.3847/1538-4357/ad13f2}, abstractNote={
 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} }
 @article{grohs_balantekin_2023, title={Implications on cosmology from Dirac neutrino magnetic moments}, volume={107}, ISSN={["2470-0029"]}, DOI={10.1103/PhysRevD.107.123502}, abstractNote={The mechanism for generating neutrino masses remains a puzzle in particle physics. If neutrino masses follow from a Dirac mass term, then neutrino states exist with opposite chirality compared to their weakly-interacting counterparts. These inactive states do not interact with their active counterparts at measurable scales in the standard model. However, the existence of these states can have implications for cosmology as they contribute to the radiation energy density at early times, and the matter energy density at late times. How Dirac neutrinos may populate thermal states via an anomalous magnetic moment operator is the focus of this work. A class of models where all neutrinos have a magnetic moment independent of flavor or chirality is considered. Subsequently, the cross sections for neutrinos scattering on background plasma particles are calculated so that the relic inactive neutrino energy is derived as a function of plasma temperature. To do so, one needs cross sections for scattering on all electrically charged standard-model particles. Therefore, the scattering cross section between a neutrino and $W$-boson via the magnetic moment vertex is derived. Current measurements put a constraint on the size of the neutrino magnetic moment from the cosmological parameter $N_{\rm eff}$ and light-element primordial abundances. Finally, how the extra Dirac states contribute to the matter energy density at late times is investigated by examining neutrino free-streaming.}, number={12}, journal={PHYSICAL REVIEW D}, author={Grohs, E. and Balantekin, A. B.}, year={2023}, month={Jun} }
 @article{grohs_richers_couch_foucart_kneller_mclaughlin_2023, title={Neutrino fast flavor instability in three dimensions for a neutron star merger}, volume={846}, ISSN={["1873-2445"]}, DOI={10.1016/j.physletb.2023.138210}, abstractNote={The flavor evolution of neutrinos in core collapse supernovae and neutron star mergers is a critically important unsolved problem in astrophysics. Following the electron flavor evolution of the neutrino system is essential for calculating the thermodynamics of compact objects as well as the chemical elements they produce. Accurately accounting for flavor transformation in these environments is challenging for a number of reasons, including the large number of neutrinos involved, the small spatial scale of the oscillation, and the nonlinearity of the system. We take a step in addressing these issues by presenting a method which describes the neutrino fields in terms of angular moments. We apply our moment method to neutron star merger conditions and show it simulates fast flavor neutrino transformation in a region where this phenomenon is expected to occur. By comparing with particle-in-cell calculations we show that the moment method is able to capture the three phases of growth, saturation, and decoherence, and correctly predicts the lengthscale of the fastest growing fluctuations in the neutrino field.}, journal={PHYSICS LETTERS B}, author={Grohs, Evan and Richers, Sherwood and Couch, Sean M. and Foucart, Francois and Kneller, James P. and McLaughlin, G. C.}, year={2023}, month={Nov} }
 @article{berryman_blinov_brdar_brinckmann_bustamante_cyr-racine_das_gouvea_denton_dev_et al._2023, title={Neutrino self-interactions: A white paper}, volume={42}, ISSN={["2212-6864"]}, DOI={10.1016/j.dark.2023.101267}, abstractNote={Neutrinos are the Standard Model (SM) particles which we understand the least, often due to how weakly they interact with the other SM particles. Beyond this, very little is known about interactions among the neutrinos, i.e., their self-interactions. The SM predicts neutrino self-interactions at a level beyond any current experimental capabilities, leaving open the possibility for beyond-the-SM interactions across many energy scales. In this white paper, we review the current knowledge of neutrino self-interactions from a vast array of probes, from cosmology, to astrophysics, to the laboratory. We also discuss theoretical motivations for such self-interactions, including neutrino masses and possible connections to dark matter. Looking forward, we discuss the capabilities of searches in the next generation and beyond, highlighting the possibility of future discovery of this beyond-the-SM physics.}, journal={PHYSICS OF THE DARK UNIVERSE}, author={Berryman, Jeffrey M. and Blinov, Nikita and Brdar, Vedran and Brinckmann, Thejs and Bustamante, Mauricio and Cyr-Racine, Francis-Yan and Das, Anirban and Gouvea, Andre and Denton, Peter B. and Dev, P. S. Bhupal and et al.}, year={2023}, month={Dec} }
 @article{gerbino_grohs_lattanzi_abazajian_blinov_brinckmann_chen_djurcic_du_escudero_et al._2023, title={Synergy between cosmological and laboratory searches in neutrino physics}, volume={42}, ISSN={["2212-6864"]}, DOI={10.1016/j.dark.2023.101333}, abstractNote={The intersection of the cosmic and neutrino frontiers is a rich field where much discovery space still remains. Neutrinos play a pivotal role in the hot big bang cosmology, influencing the dynamics of the universe over numerous decades in cosmological history. Recent studies have made tremendous progress in understanding some properties of cosmological neutrinos, primarily their energy density. Upcoming cosmological probes will measure the energy density of relativistic particles with higher precision, but could also start probing other properties of the neutrino spectra. When convolved with results from terrestrial experiments, cosmology can become even more acute at probing new physics related to neutrinos or even Beyond the Standard Model (BSM). Any discordance between laboratory and cosmological data sets may reveal new BSM physics and/or suggest alternative models of cosmology. We give examples of the intersection between terrestrial and cosmological probes in the neutrino sector, and briefly discuss the possibilities of what different laboratory experiments may see in conjunction with cosmological observatories.}, journal={PHYSICS OF THE DARK UNIVERSE}, author={Gerbino, Martina and Grohs, Evan and Lattanzi, Massimiliano and Abazajian, Kevork N. and Blinov, Nikita and Brinckmann, Thejs and Chen, Mu-Chun and Djurcic, Zelimir and Du, Peizhi and Escudero, Miguel and et al.}, year={2023}, month={Dec} }
 @article{myers_cooper_warren_kneller_mclaughlin_richers_grohs_frohlich_2022, title={Neutrino flavor mixing with moments}, volume={105}, ISSN={["2470-0029"]}, url={https://doi.org/10.1103/PhysRevD.105.123036}, DOI={10.1103/PhysRevD.105.123036}, abstractNote={The successful transition from core-collapse supernova simulations using classical neutrino transport to simulations using quantum neutrino transport will require the development of methods for calculating neutrino flavor transformations that mitigate the computational expense. One potential approach is the use of angular moments of the neutrino field, which has the added appeal that there already exist simulation codes which make use of moments for classical neutrino transport. Evolution equations for quantum moments based on the quantum kinetic equations can be straightforwardly generalized from the evolution of classical moments based on the Boltzmann equation. We present an efficient implementation of neutrino transformation using quantum angular moments in the free streaming, spherically symmetric bulb model. We compare the results against analytic solutions and the results from more exact multi-angle neutrino flavor evolution calculations. We find that our moment-based methods employing scalar closures predict, with good accuracy, the onset of collective flavor transformations seen in the multi-angle results. However in some situations they overestimate the coherence of neutrinos traveling along different trajectories. More sophisticated quantum closures may improve the agreement between the inexpensive moment-based methods and the multi-angle approach.}, number={12}, journal={PHYSICAL REVIEW D}, author={Myers, McKenzie and Cooper, Theo and Warren, MacKenzie and Kneller, Jim and McLaughlin, Gail and Richers, Sherwood and Grohs, Evan and Frohlich, Carla}, year={2022}, month={Jun} }