Sphaleron Transition Rates and the Chiral Magnetic Effect

TL;DR

This paper investigates the sphaleron transition rates and their impact on the chiral magnetic effect in high-energy nuclear collisions, comparing weak and strong coupling calculations to understand axial charge relaxation.

Contribution

It provides a comparative analysis of sphaleron rates from weak coupling and AdS/CFT calculations, highlighting differences in relaxation times relevant for the chiral magnetic effect.

Findings

AdS/CFT predicts larger relaxation times than weak coupling calculations.

Weak coupling estimates may be unreliable due to their proximity to thermalization times.

The influence of quark masses on sphaleron rates remains uncertain.

Abstract

The chiral magnetic effect is a novel quantum phenomenon proposed for high-energy nuclear collisions but which has yet to be observed. We quantify the axial charge relaxation time, due to sphalerons, which enters in simulations of this effect. An extrapolation of weak coupling calculations of the sphaleron rate yields rather different relaxation times than strong coupling AdS/CFT calculations. The AdS/CFT relaxation time is the larger one of the two by an order of magnitude, but the weak coupling relaxation time may not be reliable because it is only marginally bigger than the microscopic thermalization time. The role of quark masses has yet to be accurately assessed.