Another look at synchronized neutrino oscillations

TL;DR

This paper investigates how decoherence impacts synchronized neutrino oscillations in dense, isotropic neutrino gases, developing an exact formalism and conservation law to analyze late-time behavior and wave packet effects.

Contribution

It introduces an exact formalism and conservation law for analyzing decoherence effects on synchronized neutrino oscillations in dense neutrino backgrounds.

Findings

Identifies an exact conservation law in the neutrino system.

Develops analytical methods to study late-time decoherence effects.

Provides interpretation of decoherence via neutrino wave packet separation.

Abstract

In dense neutrino backgrounds present in supernovae and in the early Universe neutrino oscillations may exhibit complex collective phenomena, such as synchronized oscillations, bipolar oscillations and spectral splits and swaps. We consider in detail possible decoherence effects on the simplest of these phenomena -- synchronized neutrino oscillations that can occur in a uniform and isotropic neutrino gas. We develop an exact formalism of spectral moments of the flavour spin vectors describing such a system and then apply it to find analytical approaches that allow one to study decoherence effects on its late-time evolution. This turns out to be possible in part due to the existence of the (previously unknown) exact conservation law satisfied by the quantities describing the considered neutrino system. Interpretation of the decoherence effects in terms of neutrino wave packet separation is also given, both in the adiabatic and non-adiabatic regimes of neutrino flavour evolution.