Holographic equilibration in confining gauge theories under external magnetic fields

TL;DR

This paper explores how external magnetic fields influence the equilibration process in a holographic model of QCD, revealing complex quasinormal mode behaviors and a critical magnetic field where hydrodynamics fails.

Contribution

It provides the first detailed analysis of quasinormal modes in holographic QCD under magnetic fields, identifying mode crossover phenomena and a critical magnetic field for hydrodynamic breakdown.

Findings

Complex quasinormal mode trajectories depend on magnetic field, temperature, and momentum.

A critical magnetic field $B_c$ exists where hydrodynamics ceases to be valid.

Mode crossover behavior influences the equilibration dynamics.

Abstract

We investigate the effect of external magnetic fields on equilibration in the improved holographic QCD theory in the deconfined phase using the AdS/CFT correspondence. In particular we calculate the quasinormal mode spectra in the corresponding black brane solutions and study their dependence on temperature, momentum and magnetic field, both in the scalar and the shear channels. We find complex patterns in the motion of quasinormal modes on the complex plane, including certain cross overs between the lowest lying modes under varying magnetic field, momentum and temperature. We also discover a critical value of the magnetic field $B_c$ above which the hydrodynamic approximation breaks down, as the imaginary part of the first excited quasi-normal mode in the shear channel becomes smaller than that of the hydro mode.