Topologically induced local P and CP violation in QCD x QED

TL;DR

This paper explores how topological solutions in QCD and QED can induce local P and CP violation effects, such as the chiral magnetic effect, especially in intense electromagnetic fields, with potential experimental observability.

Contribution

It demonstrates how local parity-violating phenomena in QCD can be modeled using Maxwell-Chern-Simons electrodynamics and relates these effects to experimental observations like charge asymmetry in heavy ion collisions.

Findings

Topological charge fluctuations influence hadron properties.

Local P and CP violation can be described by axion electrodynamics.

Experimental evidence of charge asymmetry supports theoretical predictions.

Abstract

The existence of topological solutions and axial anomaly open a possibility of P and CP violation in QCD. For a reason that has not yet been established conclusively, this possibility is not realized in strong interactions - the experimental data indicate that a global P and CP violation in QCD is absent. Nevertheless, the fluctuations of topological charge in QCD vacuum, although not observable directly, are expected to play an important role in the breaking of $U_A(1)$ symmetry and in the mass spectrum and other properties of hadrons. Moreover, in the presence of very intense external electromagnetic fields topological solutions of QCD can induce local P- and CP-odd effects in the $SU_c(3)\times U_{em}(1)$ gauge theory that can be observed in experiment directly. Here I show how 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. Very recently, STAR Collaboration presented an observation of the electric charge asymmetry with respect to reaction plane in relativistic heavy ion collisions at RHIC.