Phases of cold holographic QCD: baryons, pions and rho mesons

TL;DR

This paper advances holographic QCD modeling by incorporating realistic pion mass and rho meson condensation, resulting in a detailed phase diagram of baryonic matter with implications for neutron-star physics.

Contribution

It introduces a more realistic holographic model of isospin-asymmetric baryonic matter, including pion and rho meson condensates, and computes the zero-temperature phase diagram.

Findings

Pion mass increases with baryon density, preventing pion condensation in neutron-star matter.

Baryons are disfavored at low baryon chemical potential even with high isospin chemical potential.

Rho meson condensation occurs at about 9.4 times the pion mass in isospin chemical potential.

Abstract

We improve the holographic description of isospin-asymmetric baryonic matter within the Witten-Sakai-Sugimoto model by accounting for a realistic pion mass, computing the pion condensate dynamically, and including rho meson condensation by allowing the gauge field in the bulk to be anisotropic. This description takes into account the coexistence of baryonic matter with pion and rho meson condensates. Our main result is the zero-temperature phase diagram in the plane of baryon and isospin chemical potentials. We find that the effective pion mass in the baryonic medium increases with baryon density and that, as a consequence, there is no pion condensation in neutron-star matter. Our improved description also predicts that baryons are disfavored at low baryon chemical potentials even for arbitrarily large isospin chemical potential. Instead, rho meson condensation sets in on top of the pion condensate at an isospin chemical potential of about $9.4\, m_\pi$. We further observe a highly non-monotonic phase boundary regarding the disappearance of pion condensation.