Limits on low energy photon-photon scattering from an experiment on magnetic vacuum birefringence

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 Polarizzazione del Vuoto con Laser apparatus [ E. Zavattini et al. Phys. Rev. D 77 032006 (2008)] at both λ=1064 and 532 nm lead to bounds on the parameter Ae, describing nonlinear 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.