# Effect of strong magnetic field on competing order parameters in two-flavor dense quark matter

## TL;DR

This study investigates how strong magnetic fields influence the coexistence and phase transitions of chiral and diquark condensates in dense quark matter, revealing magnetic field-induced changes in phase behavior relevant to neutron star physics.

## Contribution

It provides new insights into the magnetic field effects on phase structure in dense quark matter using a two-flavor NJL model, highlighting a transition from crossover to first-order phase change.

## Key findings

- Strong magnetic fields disrupt the mixed phase region.
- Magnetic fields convert smooth crossovers into first-order transitions.
- Enhanced possibility of mixed phases at high density due to magnetic effects.

## Abstract

We study the effect of strong magnetic field on competing chiral and diquark order parameters in a regime of moderately dense quark matter. The inter-dependence of the chiral and diquark condensates through nonperturbative quark mass and strong coupling effects is analyzed in a two-flavor Nambu-Jona-Lasinio (NJL) model. In the weak magnetic field limit, our results agree qualitatively with earlier zero-field studies in the literature that find a critical coupling ratio $G_D/G_S\sim 1.1$ below which chiral or superconducting order parameters appear almost exclusively. Above the critical ratio, there exists a significant mixed broken phase region where both gaps are non-zero. However, a strong magnetic field $B\gtrsim 10^{18}$ G disrupts this mixed broken phase region and changes a smooth crossover found in the weak-field case to a first-order transition for both gaps at almost the same critical density. Our results suggest that in the two-flavor approximation to moderately dense quark matter, strong magnetic field enhances the possibility of a mixed phase at high density, with implications for the structure, energetics and vibrational spectrum of neutron stars.