Spin precession and neutrino helicity flip in various spacetimes

TL;DR

This paper derives a general formula for spin precession of neutral particles in stationary, axisymmetric spacetimes and applies it to neutrinos, revealing conditions under which they undergo helicity flips with high probability.

Contribution

It introduces a comprehensive formula for spin precession in various spacetimes and analyzes neutrino helicity flip probabilities, highlighting scenarios with significant high-energy neutrino spin flips.

Findings

Low-energy neutrinos have near-unity spin-flip probability in all studied spacetimes.

High-energy neutrinos generally have negligible spin-flip probability, except in some spacetimes where it reaches unity.

The study provides insights into neutrino behavior in different gravitational backgrounds.

Abstract

We systematically study spin precession of neutral particles freely moving in spacetime. We first derive the formula describing spin precession within a general stationary and axisymmetric spacetime. We then apply our formula to study spin precession of neutral spinning particles moving within various spacetimes that are among the most ubiquitous ones found in the literature. Our results are then used to extract the helicity flip probability for neutrinos propagating in each one of those selected spacetimes. It is found that low-energy neutrinos acquire a spin-flip probability that is as large as unity in all the spacetimes considered here. The remarkable result, however, is that while spin-flip probability for high-energy neutrinos remains insignificant in most of these spacetimes, some of them do allow spin-flip probability to reach unity even for high-energy neutrinos.