Critical behaviour in QCD at finite isovector chemical potential

TL;DR

This paper investigates the critical behavior of Quantum Chromodynamics (QCD) at finite isovector chemical potential, revealing meson massless modes and symmetry breaking phenomena near the critical point at zero temperature.

Contribution

It provides the first detailed analysis of meson mass behavior and symmetry breaking in QCD at finite isovector chemical potential and zero temperature.

Findings

Charged pseudoscalar meson becomes massless at critical point

Charged pion condensation breaks O(4) symmetry

Quark number susceptibility rises near critical point

Abstract

We report an investigation of criticality in QCD at finite isovector chemical potential, mu_3, and at zero temperature. At the critical point, mu_3^c = m_pi, we find that an uncharged scalar and pseudoscalar and a charged pseudoscalar meson become massless within the resolution of our measurement. The effective long distance theory therefore breaks O(4) symmetry by charged pion condensation. This results in a rising quark number susceptibility. The baryon remains massive, as indicated by a vanishing baryon number susceptibility.