Particle Interpretations of the PVLAS Data

Understand

Recently the PVLAS collaboration reported the observation of a rotation of linearly polarized laser light induced by a transverse magnetic field -- a signal being unexpected within standard QED.

• In this review, we emphasize two mechanisms which have been proposed to explain this result: production of a single light neutral spin-zero particle or pair production of light minicharged particles.
• We discuss a class of models, involving, in addition to our familiar ``visible'' photon, further light ``hidden paraphotons'', which mix kinematically with the visible one, and further light paracharged particles.
• In these models, very strong astrophysical and cosmological bounds on the weakly interacting light particles mentioned above can be evaded.