# Neutrino spin oscillations in external fields in curved spacetime

## TL;DR

This paper investigates how neutrino spins oscillate in curved spacetime influenced by matter, electromagnetic, and gravitational fields, deriving equations and demonstrating potential resonance effects with astrophysical implications.

## Contribution

The authors derive a quasiclassical spin evolution equation for neutrinos in curved spacetime and analyze spin oscillations under combined external fields, including gravitational waves.

## Key findings

- Neutrino spin oscillations can exhibit parametric resonance in external fields.
- Derived an effective Schrödinger equation for neutrino spin dynamics.
- Numerical solutions suggest resonance effects at realistic astrophysical parameters.

## Abstract

We study spin oscillations of massive Dirac neutrinos in background matter, electromagnetic and gravitational fields. First, using the Dirac equation for a neutrino interacting with the external fields in curved spacetime, we rederive the quasiclassical equation for the neutrino spin evolution, which was proposed previously basing on principles of the general covariance. Then, we apply this result for the description of neutrino spin oscillations in nonmoving and unpolarized matter under the influence of a constant transverse magnetic field and a gravitational wave. We derive the effective Schr\"odinger equation for neutrino oscillations in these external fields and solve it numerically. Choosing realistic parameters of external fields, we show that the parametric resonance can take place in spin oscillations of low energy neutrinos. Some astrophysical applications are briefly discussed.