Talk detail

Participant	Roncadelli, Marco
Institution	INFN - Pavia - Italy - Via A. Bassi 6 - Pavia - - Italy

Session	HE1	Accepted		Order	Time
Talk	Oral abstract	Title	Enhanced transparency of the Universe in the 100 GeV - 1000 TeV band
Coauthors
Abstract	Axion-like particles (ALPs) are attracting growing interest since they are predicted by many extensions of the standard model, and in particular of superstrings and superbranes. Moreover, for suitable values of the parameters they give rise to very interesting astrophysical effects. Consider a far-away blazar emitting in the VHE band. Because photon-ALP oscillations occur in the presence of an extragalactic magnetic field B ≃ (0.1 − 1) nG, the photon acquires a split personality: it travels sometimes like a true photon and sometimes like an ALP. In the former case it undergoes EBL absorption but in the latter case is does not, and so the optical depth gets reduced with respect to the prediction of conventional physics. But since the photon survival probability is Pγ→γ = exp(−τ), even a small decrease of τ implies a large increase of Pγ→γ, which indeed means an enhanced photon transparency in the VHE band.
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