Neutrino Oscillations, Entanglement and Coherence: A Quantum Field Theory Study In Real Time

TL;DR

This paper investigates neutrino oscillations and entanglement using quantum field theory in real time, revealing finite-time effects, the limitations of the S-matrix approach, and conditions for factorization in long-baseline experiments.

Contribution

It introduces a real-time quantum field theory framework for neutrino oscillations, accounting for entanglement and finite-time corrections, and clarifies the applicability of the S-matrix in long-baseline experiments.

Findings

Finite-time corrections can be significant in long-baseline experiments.

Entanglement with charged leptons affects neutrino detection modeling.

Decay rates do not oscillate due to interference of mass eigenstates.

Abstract

The dynamics of neutrino mixing and oscillations are studied directly in finite real time in a model that effectively describes charged current weak interactions. Finite time corrections to the S-matrix result for the appearance and disappearance probabilities are obtained. It is observed that these effects may be of the same order of the S-matrix result in long-baseline appearance experiments. We argue that fundamentally, the S-matrix is ill-suited to describe long-baseline events due to the fact that the neutrino is produced in an entangled state with the charged lepton, which can be disentangled by the measurement of the charged lepton near the production site. The appearance and disappearance far-detection process is described from the time evolution of this disentangled "collapsed" state, allowing us to establish the conditions under which factorization of detection rates emerges in long-baseline experiments. We also study the time evolution of the reduced density matrix and show explicitly how oscillations are manifest in the off-diagonal terms, i.e., coherences, as a result of a finite time analysis. Lastly, we study a model for the "GSI anomaly" obtaining the time evolution of the population of parent and daughter particles directly in real time. We confirm that the decay rate of parent and growth rate of daughters do NOT feature oscillatory behavior from interference of mass eigenstates.