Have Cherenkov telescopes detected a new light boson?
  Recent observations by H.E.S.S. and MAGIC strongly suggest that the Universe
is more transparent to very-high-energy gamma rays than previously thought. We
show that this fact can be reconciled with standard blazar emission models
provided that photon oscillations into a very light Axion-Like Particle occur
in extragalactic magnetic fields. A quantitative estimate of this effect indeed
explains the observed data and in particular the spectrum of blazar 3C279.
