Lower bound for the neutrino magnetic moment from kick velocities induced at the birth of neutron stars

TL;DR

This paper proposes that neutrino chirality flips in neutron star cores can cause anisotropic neutrino escape, leading to neutron star kicks, and establishes bounds on the neutrino magnetic moment based on this mechanism.

Contribution

It introduces a novel mechanism linking neutrino magnetic moments to neutron star kicks, with bounds derived from astrophysical observations and theoretical modeling.

Findings

Neutrino magnetic moment must be at least 4.7 x 10^{-15} μ_B for efficient kick production.

Derived neutrino magnetic moment range consistent with SN 1987A data: 4.7 x 10^{-15} to (0.1-0.4) x 10^{-11} μ_B.

Predicted kick velocities match observed neutron star velocities within realistic magnetic field ranges.

Abstract

We show that the neutrino chirality flip, that can take place in the core of a neutron star at birth, is an efficient process to allow neutrinos to anisotropically escape, thus providing a to induce the neutron star kick velocities. The process is not subject to the {\it no-go theorem} since although the flip from left- to right-handed neutrinos happens at equilibrium, the reverse process does not take place given that right-handed neutrinos do not interact with matter and therefore detailed balance is lost. For simplicity, we model the neutron star core as being made of strange quark matter. We find that the process is efficient when the neutrino magnetic moment is not smaller than $4.7 \times 10^{-15}\mu_B$, where $\mu_B$ is the Bohr magneton. When this lower bound is combined with the most stringent upper bound, that uses the luminosity data obtained from the analysis of SN 1987A, our results set a range for the neutrino magnetic moment given by $4.7 \times 10^{-15} \leq \mu_\nu/\mu_B \leq (0.1 - 0.4)\times 10^{-11}$. The obtained kick velocities for natal conditions are consistent with the observed ones and span the correct range of radii for typical magnetic field intensities.