# Exact solution of multi-angle quantum many-body collective neutrino flavor oscillations

## TL;DR

This paper provides an exact many-body quantum solution for multi-angle neutrino flavor oscillations, revealing collective effects and flavor equilibration not captured by mean field approximations, with implications for astrophysical phenomena.

## Contribution

It introduces an exact quantum many-body approach to neutrino flavor oscillations considering multi-angle interactions, surpassing traditional mean field methods.

## Key findings

- Exact multi-angle neutrino interactions show collective oscillations.
- Mean field methods fail to capture flavor equilibration in certain cases.
- Entanglement entropy indicates significant quantum correlations.

## Abstract

I study the flavor evolution of a dense neutrino gas by considering vacuum contributions, matter effects and neutrino self-interactions. Assuming a system of two flavors in a uniform matter background, the time evolution of the many-body system in discretized momentum space is computed. The multi-angle neutrino-neutrino interactions are treated exactly and compared to both the single-angle approximation and mean field calculations. %The time unit chosen is $\mu_0^{-1}=(\frac{G_F}{2\sqrt{2}V})^{-1}$. The mono-energetic two neutrino beam scenario is solved analytically. I proceed to solve flavor oscillations for mono-energetic cubic lattices and quadratic lattices of two energy levels. In addition I study various configurations of twelve, sixteen, and twenty neutrinos. I find that when all neutrinos are initially of the same flavor, all methods agree. When both flavors are present, I find collective oscillations and flavor equilibration develop in the many body treatment but not in the mean field method. This difference persists in dense matter with tiny mixing angle and it can be ascribed to non-negligible flavor polarization correlations being present. Entanglement entropy is significant in all such cases. The relevance for supernovae or neutron stars mergers is contingent upon the value of the normalization volume $V$ and the large $N$ dependence of the timescale associated with oscillations. In future work, I intend to study this dependence using larger lattices and also include anti-neutrinos.