arXiv subjects

Anson Kost

Publications and source records attributed to Anson Kost.

5 recordsLinked to original sources

arXiv2026

Neutrino flavor-wave transport: Numerical tests and theoretical challenges

Neutrino quantum kinetics is computationally intractable in the neutrino-dense arenas of core-collapse supernovae and neutron star mergers. Flavor-wave (or flavomon) transport is an emerging approach to this problem in which small-scale flavor inhomogeneities are treated as quasiparticles with properties determined by the local mean background. We present the first numerical calculations of flavor-wave transport under slow driving. Our results show some quantitative successes but also underscore the theoretical challenges that need to be overcome. Two issues are particularly concerning. (1) Nonlinear wave-wave coupling may be important. (2) Degeneracies and small energy gaps are responsible for significant nonadiabatic transitions. Future work will need to address these points if flavor-wave transport is to be viable in settings of astrophysical interest. Other topics examined include flavor-wave parallel transport and flavor-space symmetry breaking.

hep-ph↗

arXiv2026

Dispersion Relations of Collective Flavor Excitations in Dense Neutrino Media

We apply the Landau damping theory to collective flavor excitations in dense neutrino media. We demonstrate explicitly that the (meta-)stable modes of the collective flavor excitations in a physical dense neutrino gas are indeed weakly damped. We show that there should in general exist infinitely many collective flavor excitation modes most of which are damped. In a neutrino gas with one or more zero crossings in the distribution of the difference of the (neutrino) lepton numbers (DLNs), the least damped resonant modes and the (originally) metastable modes at certain wave numbers can suffer from inverse Landau damping and thus become unstable. We also introduce the concept of convoluted DLN distributions which can be used to understand the physical origin of the slow and fast flavor instabilities in dense neutrino media in core-collapse supernovae and neutron star mergers.

hep-ph↗

arXiv2025

Once-in-a-lifetime encounter models for neutrino media II: Quasi-steady states and miscidynamic flavor evolution

We extended the once-in-a-lifetime encounter (OILE) model to stochastic interactions among neutrinos. As in the original OILE model, the new model reproduces the mean-field behavior of a dense neutrino gas for time $t\lesssim (\mu\gamma)^{-1}$, where $\mu$ measures the strength of the mean-field neutrino self-interaction potential and is proportional to the neutrino density, and the dimensionless "impact parameter" $\gamma$ is a measure of the change in the flavor quantum state of a neutrino during interaction with another neutrino when the wave packets of the two neutrinos overlap. As in the mean-field case, the OILE model with random neutrino velocities experiences kinetic flavor decoherence as the flavor quantum states of the neutrinos diverge from each other. Unlike the mean-field case, however, the OILE model has a "collision term" due to the quantum entanglement among neutrinos. For $\gamma\ll1$, this incoherent effect can drive the neutrinos into a quasi-steady state that is similar to the collective precession mode in a homogeneous and isotropic neutrino gas in the mean-field approximation. Subsequently, the collision term drives the neutrino gas adiabatically through different quasi-steady states and eventually to flavor equilibration. This process is an example of miscidynamic flavor evolution, with the mixing equilibria being the quasi-steady precession states.

hep-ph↗

arXiv2025

Local-equilibrium theory of neutrino oscillations

Miscidynamics describes coarse-grained neutrino transport under the assumption that flavor mixing is in local equilibrium. Here we introduce the concept of turbulent flavor-wave viscosity and develop techniques for including it in miscidynamics. This extension of the theory is necessary when neutrinos develop weak flavor instabilities as a result of astrophysical driving. The flavor-wave dispersion relation is obtained using a new and more general form of linear analysis, which does not require small flavor coherence. Flavor-wave transport is then approximated using wave kinetics and geometric optics. We hypothesize that the dynamical emergence of local oscillation invariants restricts the extent of flavor thermalization. In this view, flavor evolution is sculpted by both entropy-increasing and order-promoting factors.

hep-ph↗

arXiv2024

Once-in-a-lifetime encounter models for neutrino media: From coherent oscillations to flavor equilibration

Collective neutrino oscillations are typically studied using the lowest-order quantum kinetic equation, also known as the mean-field approximation. However, some recent quantum many-body simulations suggest that quantum entanglement among neutrinos may be important and may result in flavor equilibration of the neutrino gas. In this work, we develop new quantum models for neutrino gases in which any pair of neutrinos can interact at most once in their lifetimes. A key parameter of our models is $γ=μΔz$, where $μ$ is the neutrino coupling strength, which is proportional to the neutrino density, and $Δz$ is the duration over which a pair of neutrinos can interact each time. Our models reduce to the mean-field approach in the limit $γ\to0$ and achieve flavor equilibration in time $t \gg (γμ)^{-1}$. These models demonstrate the emergence of coherent flavor oscillations from the particle perspective and may help elucidate the role of quantum entanglement in collective neutrino oscillations.

hep-ph↗