Wess-Zumino-Witten action and photons from the Chiral Magnetic Effect

TL;DR

This paper revisits the Chiral Magnetic Effect using the chiral Lagrangian, showing its connection to the Wess-Zumino-Witten action and discussing potential photon production mechanisms related to CME.

Contribution

It demonstrates that the CME's electric-current formula derives from the Wess-Zumino-Witten action and explores photon production via the reverse CME in inhomogeneous magnetic fields.

Findings

CME current formula linked to Wess-Zumino-Witten contact term

Photon production via reverse CME can be comparable to thermal photons

CME as a signature of local parity violation, not deconfinement

Abstract

We revisit the Chiral Magnetic Effect (CME) using the chiral Lagrangian. We demonstrate that the electric-current formula of the CME is derived immediately from the contact part of the Wess-Zumino-Witten action. This implies that the CME could be, if observed, a signature for the local parity violation, but a direct evidence for neither quark deconfinement nor chiral restoration. We also discuss the reverse Chiral Magnetic Primakoff Effect, i.e. the real photon production through the vertex associated with the CME, which is kinematically possible for space-time inhomogeneous configurations of magnetic fields and the strong theta angle. We make a qualitative estimate for the photon yield to find that it comparable to the thermal photon.