Topologically induced local P and CP violation in hot QCD

TL;DR

This paper discusses how topological fluctuations in hot QCD can induce observable local P and CP violation effects, such as charge separation in heavy ion collisions, described by effective axion electrodynamics.

Contribution

It proposes that intense magnetic fields in hot QCD matter can lead to observable local P and CP violation effects, linking topological fluctuations to experimental signatures.

Findings

Evidence of charge separation observed in heavy ion collisions.

Topological fluctuations can induce local P and CP violation effects.

Effective description using Maxwell-Chern-Simons theory.

Abstract

Very stringent experimental bounds exist on the amount of P and CP violation in strong interactions. Nevertheless, the presence of non-Abelian topological solutions and the axial anomaly make the issue of CP invariance in QCD non-trivial ("the strong CP problem"). Even in the absence of a global P and CP violation the fluctuations of topological charge in the QCD vacuum are expected to play an important role in the breaking of chiral symmetry, and in the mass spectrum and other properties of hadrons. Here I argue that topological fluctuations in hot QCD matter can become directly observable in the presence of a very intense external magnetic field by inducing local P- and CP- odd effects. These local parity-violating phenomena can be described by using the Maxwell-Chern-Simons, or axion, 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.