Comments on Ultra-High-Energy Photons and D-Foam models

Understand

We revisit the constraints that the non-observation of ultra-high-energy photons due to the GZK cutoff can impose on models of Lorentz violation in photon propagation, following recent work by Maccione, Liberati and Sigl [arXiv:1003.5468] that carries further an earlier analysis by the present authors (Phys.

• Rev.
• D 63,12402 (2001), [hep-th/0012216]).
• We argue that the GZK cutoff constraint is naturally evaded in the D-brane model of space-time foam presented recently by the present authors (Phys.