Pseudoscalar-photon Interactions, Axions, Non-Minimal Extensions, and Their Empirical Constraints from Observations

TL;DR

This paper reviews the theoretical background and current experimental and observational constraints on pseudoscalar-photon interactions, focusing on axions' role in solving the strong CP problem, dark matter, and their cosmological implications.

Contribution

It provides an update on optical experiments, astrophysical constraints, and theoretical models of non-minimal interactions involving axions and photons.

Findings

Current optical experiments set bounds on pseudoscalar-photon coupling.

Astrophysical observations constrain cosmic polarization rotation.

Theoretical models explore non-minimal gravitational and electromagnetic interactions.

Abstract

Pseudoscalar-photon interactions were proposed in the study of the relations among equivalence principles. The interaction of pseudoscalar axion with gluons was proposed as a way to solve the strong CP problem. Subsequent proposal of axion as a dark matter candidate has been a focus of search. Motivation from superstring theories add to its importance. After a brief introduction and historical review, we present (i) the current status of our optical experiment using high-finesse Fabry-Perot resonant cavity - Q & A experiment - to detect pseudoscalar-photon interactions, (ii) the constraints on pseudoscalar-photon interactions from astrophysical and cosmological observations on cosmic polarization rotation, and (iii) theoretical models of non-minimal interactions of gravitational, electromagnetic and pseudoscalar (axion) fields, and their relevance to cosmology.