Nonequilibrium Dynamics of the Chiral Quark Condensate under a Strong Magnetic Field

TL;DR

This paper investigates how strong magnetic fields influence the nonequilibrium evolution of the quark condensate in QCD, using a linear sigma model and Langevin dynamics to reveal increased damping and fluctuations relevant for heavy-ion collisions and cosmology.

Contribution

It introduces a nonequilibrium quantum field theory approach to model the quark condensate dynamics under magnetic fields, highlighting the impact on dissipation and fluctuations during QCD transitions.

Findings

Magnetic fields increase the damping coefficient of the condensate.

Enhanced damping leads to greater fluctuations and longer evolution times.

The formalism can be extended to other order parameters and systems.

Abstract

Strong magnetic fields impact quantum-chromodynamics (QCD) properties in several situations; examples include the early universe, magnetars, and heavy-ion collisions. These examples share a common trait: time evolution. A prominent QCD property impacted by a strong magnetic field is the quark condensate, an approximate order parameter of the QCD transition between a high-temperature quark-gluon phase and a low-temperature hadronic phase. We use the linear sigma model with quarks to address the quark condensate time evolution under a strong magnetic field. We use the closed time path formalism of nonequilibrium quantum field theory to integrate out the quarks and obtain a mean-field Langevin equation for the condensate. The Langevin equation features dissipation and noise kernels controlled by a damping coefficient. We compute the damping coefficient for magnetic field and temperature values achieved in peripheral relativistic heavy-ion collisions and solve the Langevin equation for a temperature quench scenario. The magnetic field changes the dissipation and noise pattern by increasing the damping coefficient compared to the zero-field case. An increased damping coefficient increases fluctuations and time scales controlling condensate's short-time evolution, a feature that can impact hadron formation at the QCD transition. The formalism developed here can be extended to include other order parameters, hydrodynamic modes, and system's expansion to address magnetic field effects in complex settings as heavy-ion collisions, the early universe, and magnetars.