Magnetic structure of isospin-asymmetric QCD matter in neutron stars

TL;DR

This study uses lattice simulations to explore how magnetic fields and isospin asymmetry affect QCD matter, revealing diamagnetic behavior and shifts in pion condensation relevant to neutron star cores.

Contribution

It introduces a lattice simulation approach with a Taylor-expansion method to analyze QCD under magnetic fields and isospin chemical potentials, highlighting new effects on pion condensation and magnetic responses.

Findings

Ground state exhibits strong diamagnetism in pion condensation phase.

Magnetic fields shift pion condensation onset to higher chemical potentials.

Magnetic structure of QCD phase diagram sketched in temperature-isospin plane.

Abstract

We study QCD under the influence of background magnetic fields and isospin chemical potentials using lattice simulations. This setup exhibits a sign problem which is circumvented using a Taylor-expansion in the magnetic field. The ground state of the system in the pion condensation phase is found to exhibit a pronounced diamagnetic response. We elaborate on how this diamagnetism may contribute to the pressure balance in the inner core of strongly magnetized neutron stars. In addition we show that the onset of pion condensation shifts to larger chemical potentials due to the enhancement of the charged pion mass for growing magnetic fields. Finally, we sketch the magnetic structure of the QCD phase diagram in the temperature-isospin chemical potential plane.