The PVLAS experiment has built an apparatus to measure rotations and ellipticities induced by a transverse magnetic field onto linearly polarized laser light.Available results can be interpreted as observation of an unexpectedly large rotation effect between 10-7 and 4 10-7rad. If this rotation is due to the existence of a light spin zero boson of mass m and coupling to two photons 1/M, the ball-park values of the boson mass parameters are m=1meV and M=10+6GeV.
Comment: 8 pages, 3 figures, paper presented at the XXXXth Rencontres de Moriond, Electroweak interactions and unified theories, La Thuile, Aosta Valley, Italy, March 5-12 2005