Prospects for constraining quantum gravity dispersion with near term observations

TL;DR

This paper explores the potential of using high-energy photons from gamma ray bursts observed by Fermi to constrain or measure quantum gravity effects on light dispersion, with implications for fundamental physics theories.

Contribution

It assesses the prospects of detecting quantum gravity dispersion effects with current and near-term observations, proposing methods to distinguish such effects from astrophysical sources.

Findings

Fermi has observed eight photons over 100 MeV in 10 months.

Possible bounds on in-vacuo dispersion are discussed based on these observations.

Higher energy photons and neutrinos could reveal quantum gravity effects with delays of days to months.

Abstract

We discuss the prospects for bounding and perhaps even measuring quantum gravity effects on the dispersion of light using the highest energy photons produced in gamma ray bursts measured by the Fermi telescope. These prospects are brigher than might have been expected as in the first 10 months of operation Fermi has reported so far eight events with photons over 100 MeV seen by its Large Area Telescope (LAT). We review features of these events which may bear on Planck scale phenomenology and we discuss the possible implications for the alternative scenarios for in-vacua dispersion coming from breaking or deforming of Poincare invariance. Among these are semi-conservative bounds, which rely on some relatively weak assumptions about the sources, on subluminal and superluminal in-vacuo dispersion. We also propose that it may be possible to look for the arrival of still higher energy photons and neutrinos from GRB's with energies in the range 10^14 - 10^17 eV. In some cases the quantum gravity dispersion effect would predict these arrivals to be delayed or advanced by days to months from the GRB, giving a clean separation of astrophysical source and spacetime propagation effects.