Chiral Magnetic Wave

TL;DR

This paper predicts a new collective excitation called the Chiral Magnetic Wave in relativistic plasmas with chiral fermions, arising from quantum anomalies, and explores its properties through multiple theoretical approaches.

Contribution

It introduces the Chiral Magnetic Wave as a novel gapless excitation in chiral plasmas, derived from anomaly considerations, and analyzes its characteristics using hydrodynamics, reduced models, and holography.

Findings

Existence of the Chiral Magnetic Wave demonstrated

Properties studied via three different theoretical frameworks

Implications for heavy ion collision phenomenology discussed

Abstract

We consider a relativistic plasma containing charged chiral fermions in an external magnetic field, e.g a chirally symmetric quark-gluon plasma created in relativistic heavy ion collisions. We show that triangle anomalies imply the existence of a new type of collective gapless excitation in this system that stems from the coupling between the density waves of the electric and chiral charges; we call it "the Chiral Magnetic Wave" (CMW). The CMW exists even in a neutral plasma, i.e. in the absence of the axial and vector chemical potentials. We demonstrate the existence of CMW and study its properties using three different approaches: i) relativistic magnetohydrodynamics; ii) dimensional reduction to $(1+1)$ Sine-Gordon model, appropriate in a strong magnetic field; and iii) holographic QCD (Sakai-Sugimoto model), appropriate at strong coupling. We also briefly discuss the phenomenological implications of the CMW for heavy ion collisions.