Anomaly induced effects in a magnetic field

TL;DR

This paper explores a modified electrodynamics model with a light massive vector field coupled via Chern-Simons terms, predicting observable effects in magnetic field experiments similar to axion-like particles, while avoiding certain astrophysical bounds.

Contribution

It introduces a new electrodynamics modification involving a light massive vector field with Chern-Simons coupling, providing a framework compatible with experimental searches and avoiding stellar and CMB bounds.

Findings

Predicts observable effects in magnetic field experiments similar to axion-like particles.

Proposes a microscopic origin involving gauge anomaly cancellation with millicharged fermions.

Avoids stellar and CMB bounds, allowing for positive experimental detection.

Abstract

We consider a modification of electrodynamics by an additional light massive vector field, interacting with the photon via Chern-Simons-like coupling. This theory predicts observable effects for the experiments studying the propagation of light in an external magnetic field, very similar to those, predicted by theories of axion and axion-like particles. We discuss a possible microscopic origin of this theory from a theory with non-trivial gauge anomaly cancellation between massive and light particles (including, for example, millicharged fermions). Due to the conservation of the gauge current, the production of the new vector field is suppressed at high energies. As a result, this theory can avoid both stellar bounds (which exist for axions) and the bounds from CMB considered recently, allowing for positive results in experiments like ALPS, LIPPS, OSQAR, PVLAS-2, BMV, Q&A, etc.