Neutrino many-body flavor evolution: the full Hamiltonian

TL;DR

This paper investigates neutrino flavor evolution using a full quantum many-body Hamiltonian, including non-forward scattering, revealing faster flavor changes and thermalization in small neutrino systems.

Contribution

It introduces a comprehensive quantum many-body framework with full Hamiltonian including non-forward terms, advancing understanding of neutrino flavor dynamics.

Findings

Non-forward scattering accelerates flavor evolution.

Small systems show thermalization of flavor and momentum.

Results align with microcanonical ensemble predictions.

Abstract

We study neutrino flavor evolution in the quantum many-body approach using the full neutrino-neutrino Hamiltonian, including the usually neglected terms that mediate non-forward scattering processes. Working in the occupation number representation with plane waves as single-particle states, we explore the time evolution of simple initial states with up to $N=10$ neutrinos. We discuss the time evolution of the Loschmidt echo, one body flavor and kinetic observables, and the one-body entanglement entropy. For the small systems considered, we observe `thermalization' of both flavor and momentum degrees of freedom on comparable time scales, with results converging towards expectation values computed within a microcanonical ensemble. We also observe that the inclusion of non-forward processes generates a faster flavor evolution compared to the one induced by the truncated (forward) Hamiltonian.