Magnetic Moment of Constituent Fermions in Strongly Interacting Matter

TL;DR

This paper explores how constituent fermions in strongly interacting matter develop a macroscopic magnetic moment in high-density, chiral symmetry-breaking phases, potentially explaining the origin of magnetars.

Contribution

It demonstrates the generation of a macroscopic magnetization in a high-density, chiral symmetry-broken phase, linking microscopic fermion properties to astrophysical magnetic fields.

Findings

Magnetization arises in the high-density, spin-polarized phase.

Magnetization increases as the fermion mass VEV decreases.

High magnetic fields could destabilize the dense matter state, relevant for neutron stars.

Abstract

We investigate the magnetic moment operator for constituent fermion masses for chirally symmetric theories. Constituent fermion masses are generated through a yukawa interaction of the fermion with a scalar (or /and psuedoscalar) field via the vacuum expectation value (VEV) of the scalar (or and psuedoscalar) field. We especially consider the high baryon density $\pi_0$ condensed phase, in which chiral symmetry is spontaneously broken, with space varying expectation values of the $ \sigma$ and $\pi_0$ fields. This phase has a spin polarized fermi sea as the ground state. We show that there is indeed generated a macroscopic magnetization in this phase, contrary to what one would have found, if one just used a primitive phenomenological magnetic moment formula for explicit/ current fermion masses. Furthermore, this analysis reveals that the magnetization of this state goes up as the VEV, that determines the 'mass', comes down with increasing baryon density. The consequent high magnetic field that is generated will destabilize this state at a threshold density. This is important in the context of neutron stars, as such a high density state may be responsible for very high magnetic fields in the dense core of neutron stars. This could potentially be the origin of magnetars - the stars with the largest magnetic fields in the universe.