Ultra high energy photons as probes of Lorentz symmetry violations in stringy space-time foam models

TL;DR

This paper challenges the use of gamma-ray time delays to test quantum gravity models, showing that stringy space-time foam models predict excessive ultra-high energy photons, leading to stronger constraints than time delay observations.

Contribution

It demonstrates that stringy space-time foam models are inconsistent with observed ultra-high energy cosmic ray fluxes, providing tighter constraints than those from gamma-ray time delay measurements.

Findings

Stringy space-time foam models predict too many ultra-high energy photons.

Constraints from cosmic ray fluxes are stronger than those from time delay observations.

Quantum gravity effects are too small to explain observed gamma-ray time delays.

Abstract

The time delays between gamma-rays of different energies from extragalactic sources have often been used to probe quantum gravity models in which Lorentz symmetry is violated. It has been claimed that these time delays can be explained by or at least put the strongest available constraints on quantum gravity scenarios that cannot be cast within an effective field theory framework, such as the space-time foam, D-brane model. Here we show that this model would predict too many photons in the ultra-high energy cosmic ray flux to be consistent with observations. The resulting constraints on the space-time foam model are much stronger than limits from time delays and allow for Lorentz violations effects way too small for explaining the observed time delays.