Anti GZK for Photons?

The Greisen-Zatsepin-Kuzmin cutoff tells us that charged particles don't make it through the Cosmic Microwave Background (CMB) photon radiation. High energy protons just hit low energy photons and voilà, we lose them. Nevertheless there are indications that high energy photons fare better; the CMB seems to be more transparent to them.

I don't understand this, because long ago, I studied Sakurai's Vector Meson Dominance (VMD) Model , at the energies then available, early 70s, it was doing fine. The model used the Lorentz character of photons and vector mesons to study processes with either of them with a unified approach. All one had to do was to factor out the different strengths of electromagnetic and hadron forces.

The results presented in the New Scientist article above, put this into question at high enough energies.

Phenomenologically though, one can definitely break Lorentz invariance; this being an old game for physicists, and see what happens.

Giovanni Amelino-Camelia et al. do just that in:

Threshold anomalies in Horava-Lifshitz-type theories

Once this breakdown is allowed, even Poincaré symmetry is broken, one can start to make sense on the High Energy Gamma Rays Transparent Universe (awful acronym I'm sure nobody will use, HEGRTU).

Maybe this phrase will be more memorable. Anti GZK for Photons. (AGZKP, I doubt it).

What I mean by that, is that protons are not allowed at high energies, but photons are. This is really unaesthetic, and unfair, but if true; the LAGO collaboration of which I am a member, may have a shot at  fifteen minutes of fame.

LAGO, an upshot from AUGER, will benefit from this asymmetry, and both collaborations would be famous. One for showing that GZK is there for protons, and the other for showing that it is not there for photons. No wonder we didn't think of that before, that will be really ugly. It will prove that the heavens are really much less than perfect.

Sayonara, Plato!