Coherence and oscillations of cosmic neutrinos

TL;DR

This paper investigates how cosmic neutrinos lose coherence and how their spectrum broadens due to magnetic fields and interactions, affecting their oscillation behavior over cosmological distances.

Contribution

It provides a detailed analysis of neutrino wavepacket evolution in various astrophysical environments, highlighting the dominant role of magnetic fields in coherence loss.

Findings

Magnetic fields >10 Gauss cause neutrino coherence loss over cosmic distances.

High magnetic fields (>10^9 Gauss) and PeV energies lead to spectral broadening.

Coherent broadening can significantly modify the neutrino energy spectrum.

Abstract

For cosmic neutrinos we study the conditions and the effects of the coherence loss as well as coherent broadening of the spectrum. We evaluate the width of the neutrino wavepacket produced by charged particles under various circumstances: in an interaction-free environment, in a radiation-dominated medium (typical of the sources of the gamma ray bursts) and in the presence of a magnetic field. The effect of the magnetic field on the wavepacket size appears to be more important than the scattering. If the magnetic field at the source is larger than $\sim$10 Gauss, the coherence of neutrinos will be lost while traveling over cosmological distances. Various applications of these results have been considered. We find that for large magnetic fields ($B> 10^9$ Gauss) and high energies ($E_\nu>{\rm PeV}$), "coherent broadening" can modify the energy spectrum of neutrinos. In the coherent case, averaging out the oscillatory terms of the probabilities does not induce any statistical uncertainty beyond what expected in the absence of these terms. A deviation from the standard quantum mechanics that preserves average energy and unitarity cannot alter the picture.