Light Pseudoscalar Bosons, PVLAS and the Double Pulsar J0737-3039

Light Pseudoscalar Bosons (LPBs) coupled to two photons are predicted by many realistic extensions of the Standard Model and give rise to birefringence and dichroism in a light beam travelling in an external magnetic field. These effects have recently been detected by the PVLAS collaboration, thereby strongly suggesting the existence of a LPB. We provide an astrophysical cross-check for such a claim. Actually, we show that in the double pulsar J0737-3039 photon-LPB conversion can give rise to a characteristic attenuation pattern of the light beam emitted by one of the pulsars when it goes through the magnetosphere of the companion. The effect under consideration shows up in the $\gamma$-ray band and can be detected by the upcoming GLAST mission.