Chern-Simons current and local parity violation in hot QCD matter

TL;DR

This paper discusses how topological fluctuations in hot QCD matter, under intense magnetic fields, can lead to observable local P and CP violations, notably through the chiral magnetic effect in heavy ion collisions.

Contribution

It introduces a framework using Maxwell-Chern-Simons electrodynamics to describe local parity violations in hot QCD matter induced by topological fluctuations and magnetic fields.

Findings

Evidence of charge separation in heavy ion collisions from STAR Collaboration.

Theoretical link between topological fluctuations and observable P/CP violation.

Proposal of Maxwell-Chern-Simons theory as an effective description.

Abstract

Non-Abelian gauge theories "live" in a space-time with non-trivial topology that can be characterized by an odd-dimensional Chern-Simons form. In QCD, Chern-Simons form is induced by the chiral anomaly and the presence of topological solutions; it opens a possibility for the breaking of P and CP invariances in strong interactions ("the strong CP problem"). While there is apparently no global P and CP violation in QCD, here I argue that topological fluctuations in hot quark-gluon matter can become directly observable in the presence of a very intense external magnetic field by inducing local P- and CP- odd effects. These phenomena can be described by using the Maxwell-Chern-Simons electrodynamics as an effective theory. Local P and CP violation in hot QCD matter can be observed in experiment through the "chiral magnetic effect" - the separation of electric charge along the axis of magnetic field that is created by the colliding relativistic ions. There is a recent evidence for the electric charge separation relative to the reaction plane of heavy ion collisions from the STAR Collaboration at RHIC.