PVLAS results on laser production of axion-like dark matter candidate particles

Microscopic processes in the quantum vacuum, such as photon-photon scattering and the Primakoff effect, where light, neutral, scalar/pseudoscalar particles are produced from a two-photon vertex, could give rise, in the presence of an external magnetic field, to macroscopically observable optical phenomena, such as vacuum birefringence and dichroism. Such particles are candidate constituents of the Cold Dark Matter. The PVLAS collaboration is operating a high-sensitivity (similar to 10(-7) 1/root Hz) optical ellipsometer capable of detecting very small changes in the light polarisation state induced by a strong transverse magnetic field on a linearly polarised laser beam. This ellipsometer is capable of measuring vacuum birefringences and dichroisms, in an independent way, down to levels below 10(-8) rad, for about one hour of data taking time. Preliminary results, involving the observation of candidate signals in vacuum, will be discussed