Out-of-equilibrium chiral magnetic effect from chiral kinetic theory

Yin Jiang,Jinfeng Liao,Shuzhe Shi,Pengfei Zhuang,Anping Huang

doi:10.1016/j.physletb.2017.12.025

Abstract

Recently there has been significant interest in the macroscopic manifestation of chiral anomaly in many-body systems of chiral fermions. A notable example is the Chiral Magnetic Effect (CME). Enthusiastic efforts have been made to search for the CME in the quark-gluon plasma created in heavy ion collisions. A crucial challenge is that the extremely strong magnetic field in such collisions may last only for a brief moment and the CME current may have to occur at so early a stage that the quark-gluon matter is still far from thermal equilibrium. This thus requires modeling of the CME in an out-of-equilibrium setting. With the recently developed theoretical tool of chiral kinetic theory, we make a first phenomenological study of the CME-induced charge separation during the pre-thermal stage in heavy ion collisions. The effect is found to be very sensitive to the time dependence of the magnetic field and also influenced by the initial quark momentum spectrum as well as the relaxation time of the system evolution toward thermal equilibrium. Within the present approach, such pre-thermal charge separation is found to be modest.

Highlights

Spin-1 2 fermions that are massless are unique in that the axial symmetry in their classical description gets broken in quantized theory, a fundamental feature known as the chiral anomaly [1,2]
We introduce a quantity R Q = N Q /Ntotal defined as a ratio of the total number of net charge on the x − y plane at time τ = 0.2 fm/c
The R Q monotonically grows with time in all cases, reflecting the accumulation of charge separation from continuous Chiral Magnetic Effect (CME) transport

Summary

Introduction

1 2 fermions that are massless (or approximately so) are unique in that the axial symmetry in their classical description gets broken in quantized theory, a fundamental feature known as the chiral anomaly [1,2]. Examples of such chiral fermions include e.g. light quarks/leptons in the Standard Model of Particle Physics or emergent quantum states of electrons in the so-called Dirac and. Enthusiastic efforts have been made to search for manifestation of these effects in two known types of chiral matter, the quark-gluon plasma (QGP) produced in heavy ion collisions [14,15,16,17] as well as the Dirac and Weyl semimetals [18,19,20,21].

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