Comparison of QG-Induced Dispersion with Standard Physics Effects

TL;DR

This paper compares quantum gravity-induced dispersion effects on gamma-ray propagation with standard physics effects, finding that quantum effects dominate at first order, while standard effects are smaller or have different energy dependencies.

Contribution

It provides a detailed analysis of standard physics effects that could mimic or mask quantum gravity dispersion in gamma-ray observations.

Findings

Quantum gravity effects are larger than standard physics effects at first order.

Standard physics effects are smaller but can be comparable at second order.

Different energy dependencies help distinguish quantum gravity effects from standard physics.

Abstract

One of the predictions of quantum gravity phenomenology is that, in situations where Planck-scale physics and the notion of a quantum spacetime are relevant, field propagation will be described by a modified set of laws. Descriptions of the underlying mechanism differ from model to model, but a general feature is that electromagnetic waves will have non-trivial dispersion relations. A physical phenomenon that offers the possibility of experimentally testing these ideas in the foreseeable future is the propagation of high-energy gamma rays from GRB's at cosmological distances. With the observation of non-standard dispersion relations within experimental reach, it is thus important to find out whether there are competing effects that could either mask or be mistaken for this one. In this letter, we consider possible effects from standard physics, due to electromagnetic interactions, classical as well as quantum, and coupling to classical geometry. Our results indicate that, for currently observed gamma-ray energies and estimates of cosmological parameter values, those effects are much smaller than the quantum gravity one if the latter is first-order in the energy; some corrections are comparable in magnitude with the second-order quantum gravity ones, but they have a very different energy dependence.