Can the PVLAS particle be compatible with the astrophysical bounds?

The PVLAS collaboration has announced recently the observation dichroism and birefringence of vacuum permeated by a intense magnetic field. Both are typical predictions of the existence of light particles that, as the QCD axion, interact with the electromagnetic field. The strength of the interaction as inferred from the PVLAS measurements is however strongly excluded by astrophysical arguments and axion Helioscopes since these particles, as neutrinos, would be copiously produced in the interior of the Sun. In this Thesis several refined models are presented where the astrophysical bounds are severely relaxed, allowing the PVLAS particle interpretation. All these models involve the existence of further new particles, in particular paraphotons and millicharged particles. Also a model-independent study is performed, showing that the reconciliation of the PVLAS particle interpretation implies new low energy physics, usually accessible to precision experiments. Finally, if the PVLAS particle would be parity even, the strongest exclusion bounds would come, not from astrophysics, but from experiments searching for 5th type forces.