  We show that photons with energies above the GZK cutoff can reach us from
very distant sources if they mix with light axions in extragalactic magnetic
fields. The effect which enables this is the conversion of photons into axions,
which are sufficiently weakly coupled to travel large distances unimpeded.
These axions then convert back into high energy photons close to the Earth. We
show that photon-axion mixing facilitates the survival of super-GZK photons
most efficiently with a photon-axion coupling scale of order 10^11 GeV, which
is in the same range as the scale for the photon-axion mixing explanation for
the dimming of supernovae without cosmic acceleration. We discuss possible
observational consequences of this effect.
