Exploring the axion potential and axion walls in dense quark matter
B. X. Zhang, David Alvarez-Castillo, A. G. Grunfeld, Marco Ruggieri
Abstract
We study the axion of quantum chromodynamics in hot and/or dense quark matter, within a Nambu-Jona-Lasinio-like model that includes the coupling of the axion to quarks. First, we compute the effects of the chiral crossover on the axion mass and self-coupling at finite temperature and baryon density, implementing local electrical neutrality and $\ensuremath{\beta}$-equilibrium. We find that the low energy properties of axion are very sensitive to the phase transition of quantum chromodynamics, in particular, when the bulk quark matter is close to criticality. Then, for the first time in the literature we compute the axion potential at finite quark chemical potential and study the axion domain walls in bulk quark matter. We find that the energy barrier between two adjacent vacuum states decrease in the chirally restored phase: this results in a lower surface tension of the walls. Finally, we comment on the possibility of production of walls in dense quark matter.