Strange quark mass turns magnetic domain walls into multi-winding flux tubes

TL;DR

This paper investigates how the strange quark mass influences magnetic flux tubes in dense quark matter, revealing a cascade of multi-winding flux tubes with unique structures that could appear in the QCD phase diagram under magnetic fields.

Contribution

It introduces the effect of finite strange quark mass on magnetic flux tubes in dense quark matter, extending previous models that neglected this mass.

Findings

Multi-winding flux tubes form as remnants of magnetic domain walls with increasing strange quark mass.

Flux tubes with winding numbers >1 can survive up to 20% of the quark chemical potential.

Unconventional ring-like magnetic field structures are observed in these flux tubes.

Abstract

Dense quark matter is expected to behave as a type-II superconductor at strong coupling. It was previously shown that if the strange quark mass $m_s$ is neglected, magnetic domain walls in the so-called 2SC phase are the energetically preferred magnetic defects in a certain parameter region. Computing the flux tube profiles and associated free energies within a Ginzburg-Landau approach, we find a cascade of multi-winding flux tubes as "remnants" of the domain wall when $m_s$ is increased. These flux tubes exhibit an unconventional ring-like structure of the magnetic field. We show that flux tubes with winding numbers larger than one survive for values of $m_s$ up to about 20% of the quark chemical potential. This makes them unlikely to play a significant role in compact stars, but they may appear in the QCD phase diagram in the presence of an external magnetic field.