  We study the photon axion mixing in the presence of large extra dimensions.
The eigenvalues and eigenstates of the mixing matrix are analyzed and we
establish the resonance condition for the total conversion of a high energy
photon into a Kaluza-Klein (KK) axion state. This resonant transition, a photon
transformed into a KK axion travelling freely through the bulk and converting
back into a photon, may provide a plausible explanation for the transparency of
the universe to energetic photons. If the brane we live in is curved, then
there are shortcuts through the bulk, which the axion can take. Within our
model, the photons having the appropriate resonance energy are using the
axionic shortcut and arrive earlier compared to the photons which follow the
geodesic on the brane. We suggest that such axionic shortcuts are at the root
of the dispersion of time arrival of photons observed by the MAGIC telescope.
We indicate also the cosmological significance of the existence of axionic
shortcuts for the photon.
