Limits on quantum gravity effects from Swift short gamma-ray bursts

TL;DR

This paper uses observations of short gamma-ray bursts to set new limits on quantum gravity effects, specifically testing Lorentz invariance violation by analyzing photon arrival times.

Contribution

It provides a more robust and improved constraint on the quantum gravity energy scale using a sample of short GRBs, reducing uncertainties from intrinsic source delays.

Findings

Limit on E_QG > 1.5 x 10^16 GeV

Short GRBs are ideal for LIV tests due to lack of intrinsic spectral lag

Results improve upon previous constraints from long GRBs

Abstract

The delay in the arrival times between high and low energy photons from cosmic sources can be used to test the violation of the Lorentz invariance (LIV), predicted by some quantum gravity theories, and to constrain its characteristic energy scale ${\rm E_{QG}}$ that is of the order of the Planck energy. Gamma-ray bursts (GRBs) and blazars are ideal for this purpose thanks to their broad spectral energy distribution and cosmological distances: at first order approximation, the constraints on ${\rm E_{QG}}$ are proportional to the photon energy separation and the distance of the source. However, the LIV tiny contribution to the total time delay can be dominated by intrinsic delays related to the physics of the sources: long GRBs typically show a delay between high and low energy photons related to their spectral evolution (spectral lag). Short GRBs have null intrinsic spectral lags and are therefore an ideal tool to measure any LIV effect. We considered a sample of $15$ short GRBs with known redshift observed by Swift and we estimate a limit on ${\rm E_{QG}}\gtrsim 1.5\times 10^{16}$ GeV. Our estimate represents an improvement with respect to the limit obtained with a larger (double) sample of long GRBs and is more robust than the estimates on single events because it accounts for the intrinsic delay in a statistical sense.