# Permanent mean spin source of the chiral magnetic effect in neutron stars

## TL;DR

This paper extends the AMHD framework to include mean spin effects in neutron star cores, showing how it can explain the growth of magnetic fields up to 10^18 G in old neutron stars, relevant for understanding magnetar fields.

## Contribution

It introduces a generalized AMHD model incorporating mean spin effects, providing a mechanism for magnetic field amplification in neutron stars.

## Key findings

- Magnetic fields can grow up to 10^18 G in old neutron stars.
- The model explains magnetic field evolution consistent with observed magnetar fields.
- Growth occurs during the neutrino cooling era, neglecting turbulence and assuming rigid rotation.

## Abstract

We suggest the generalization of the Anomalous Magneto-Hydro-Dynamics (AMHD) in the chiral plasma of a neutron star (NS) accounting for the mean spin in the ultrarelativistic degenerate electron gas within the magnetized NS core as a continuing source of the chiral magnetic effect. Using the mean field dynamo model generalized in AMHD, one can obtain the growth of a seed magnetic field up to $10^{18}\,\text{G}$ for an old non-superfluid NS at its neutrino cooling era $t < 10^6\,\text{yr}$, while neglecting any matter turbulence within its core and assuming the rigid NS rotation. The application of the suggested approach to the evolution of magnetic fields observed in magnetars, $B\sim 10^{15}\,\text{G}$, should be self-consistent with all approximations used in the suggested laminar dynamo, at least, up to the jumps of growing fields.