Neutrino production states in oscillation phenomena - are they pure or mixed?

TL;DR

This paper examines whether neutrino production states are pure or mixed, considering effects like Lorentz transformations and beyond Standard Model interactions, to clarify their quantum state nature in oscillation phenomena.

Contribution

It analyzes the purity or mixture of neutrino states considering relativistic effects, helicity states, and extended Standard Model parameters, providing new insights into neutrino quantum states.

Findings

Neutrino states can be mixed depending on energy and interaction parameters.

Wigner spin rotation affects the neutrino state description in different frames.

Subdominant helicity states and multiple mixing matrices influence neutrino state purity.

Abstract

General quantum mechanical states of neutrinos produced by mechanisms outside the Standard Model are discussed. The neutrino state is described by the Maki-Nakagawa-Sakata-Pontecorvo unitary mixing matrix only in the case of relativistic neutrinos and Standard Model left-handed charge current interaction. The problem of Wigner spin rotation caused by Lorentz transformation from the rest production frame to the laboratory frame is considered. Moreover, the mixture of the neutrino states as a function of their energy and parameters from the extension of the Standard Model are investigated. Two sources of mixture, the appearance of subdominant helicity states, and mass mixing with several different mixing matrices are studied.