Pion quasiparticles in isospin medium from holography

TL;DR

This paper investigates pion quasiparticles in hot, dense isospin media using holographic models, revealing how their masses and widths depend on temperature and isospin chemical potential, and identifying the superfluid phase transition.

Contribution

It provides a holographic analysis of pion quasiparticle properties in isospin medium, including mass splitting and phase transition behavior, which is a novel application of AdS/QCD models.

Findings

Screening masses increase with temperature.

Charged pion screening masses decrease with isospin chemical potential.

The charged pion becomes massless at the superfluid transition.

Abstract

The properties of the pion quasiparticle in hot and dense isospin medium, including the temperature and isospin chemical potential dependence of their screening mass, pole mass and thermal width, as well as their relationships with the pion superfluid phase transition, are investigated in the framework of two-flavor ($N_{f}=2$) soft-wall AdS/QCD models. We extract the screening mass of the pion from the pole of the spatial two-point Retarded correlation function. We find that the screening masses of both neutral and charged pions increase monotonously with the increasing of temperature. However, the isospin chemical potential $\mu_{I}$ would depress the screening masses of the charged pions, $m_{\pi^{\pm},\rm{scr}}$. With the increasing of $\mu_{I}$, $m_{\pi^{\pm},\rm{scr}}$ monotonically decrease to zero on the boundary between the normal phase and the pion superfluid phase, while the screening mass of the neutral pion, $m_{\pi^0,\rm{scr}}$, remains almost unchanged. The pole mass $m_{\rm{pole}}$ and thermal width $\Gamma$ of the pion are extracted from the pole of temporal two-point Retarded correlation function, i.e., the corresponding quasi-normal frequencies, $\omega=m_{\rm{pole}}-i\Gamma/2$. The results show that the pole masses of the three modes ($\pi^0, \pi^+, \pi^-$) are splitting at finite $\mu_{I}$. The thermal widths of the three modes monotonically increase with temperature. Furthermore, the pole mass of $\pi^+$ decreases almost linearly with the increasing of $\mu_{I}$ and reaches zero at $\mu_{I}=\mu_{I}^c$, It means that $\pi^+$ becomes a massless Goldstone boson of the pion superfluid phase transition.