New PVLAS model independent limit for the axion coupling to $\gamma\gamma$ for axion masses above 1meV

TL;DR

The PVLAS experiment set a new model-independent upper limit on axion-photon coupling for axion masses above 1 meV by measuring vacuum magnetic birefringence, with no ellipticity signal detected after extensive data collection.

Contribution

This work provides the first model-independent constraint on axion-photon coupling for masses above 1 meV using vacuum birefringence measurements.

Findings

No ellipticity signal detected within noise limits.

Established the best model-independent upper limit on axion-photon coupling for masses >1 meV.

Measured vacuum magnetic birefringence consistent with QED predictions.

Abstract

During 2014 the PVLAS experiment has started data taking with a new apparatus installed at the INFN Section of Ferrara, Italy. The main target of the experiment is the observation of magnetic birefringence of vacuum. According to QED, the ellipticity generated by the magnetic birefringence of vacuum in the experimental apparatus is expected to be $\psi^{\rm(QED)} \approx 5\times10^{-11}$. No ellipticity signal is present so far with a noise floor $\psi^{\rm(noise)} \approx 2.5\times10^{-9}$ after 210 hours of data taking. The resulting ellipticity limit provides the best model independent upper limit on the coupling of axions to $\gamma\gamma$ for axion masses above $10^{-3}$eV.