Anisotropic pressure in dense neutron matter under the presence of a strong magnetic field

TL;DR

This paper investigates how extremely strong magnetic fields cause anisotropic pressure in dense neutron matter, leading to instability at high fields, with implications for magnetar core physics.

Contribution

It provides a detailed analysis of pressure anisotropy and instability thresholds in neutron matter under ultra-strong magnetic fields using Skyrme effective forces.

Findings

Pressure anisotropy becomes significant above 10^{18} G.

Longitudinal pressure vanishes at critical fields 10^{18}-10^{19} G.

Different Skyrme forces affect the thresholds and behavior of neutron matter.

Abstract

Dense neutron matter with recently developed BSk19 and BSk21 Skyrme effective forces is considered in magnetic fields up to $10^{20}$ G at zero temperature. The breaking of the rotational symmetry by the magnetic field leads to the differentiation between the pressures along and perpendicular to the field direction which becomes significant in the fields $H>H_{th}\sim10^{18}$ G. The longitudinal pressure vanishes in the critical field $10^{18}<H_c\lesssim10^{19}$ G, resulting in the longitudinal instability of neutron matter. For the Skyrme force fitted to the stiffer underlying equation of state (BSk21 vs. BSk19) the threshold $H_{th}$ and critical $H_c$ magnetic fields become larger. The longitudinal and transverse pressures as well as the anisotropic equation of state of neutron matter are determined under the conditions relevant for the cores of magnetars.