Experimental bounds on induced vacuum magnetic birefringence can be used to improve present photon-photon scattering limits in the electronvolt energy range. Measurements with the PVLAS apparatus (E. Zavattini {\it et al.}, Phys. Rev. D {\bf77} (2008) 032006) at both λ=1064 nm and 532 nm lead to bounds on the parameter {\it Ae}, describing non linear effects in QED, of Ae(1064)<6.6⋅10−21 T−2 @ 1064 nm and Ae(532)<6.3⋅10−21 T−2 @ 532 nm, respectively, at 95% confidence level, compared to the predicted value of Ae=1.32⋅10−24 T−2. The total photon-photon scattering cross section may also be expressed in terms of Ae, setting bounds for unpolarized light of σγγ(1064)<4.6⋅10−62 m2 and σγγ(532)<2.7⋅10−60 m2. Compared to the expected QED scattering cross section these results are a factor of ≃2⋅107 higher and represent an improvement of a factor about 500 on previous bounds based on ellipticity measurements and of a factor of about 1010 on bounds based on direct stimulated scattering measurements.
@article{arxiv.0805.3036,
title = {Limits on Low Energy Photon-Photon Scattering from an Experiment on Magnetic Vacuum Birefringence},
author = {M. Bregant and G. Cantatore and S. Carusotto and R. Cimino and F. Della Valle and G. Di Domenico and U. Gastaldi and M. Karuza and V. Lozza and E. Milotti and E. Polacco and G. Raiteri and G. Ruoso and E. Zavattini and G. Zavattini},
journal= {arXiv preprint arXiv:0805.3036},
year = {2008}
}