Light Speed Variation in a String Theory Model for Space-Time Foam

TL;DR

This paper explores a string theory model predicting quantum-gravity-induced light speed variations, connecting theoretical predictions with gamma-ray burst observations and deriving constraints from recent high-energy photon data.

Contribution

It introduces a supersymmetric string model for space-time foam that predicts observable light speed fluctuations and derives related quantum-gravity parameters, linking theory with experimental data.

Findings

Gamma-ray burst photon delays support the model.

Derived the effective quantum-gravity mass.

Constraints from high-energy photon observations are consistent.

Abstract

We revisit a supersymmetric string model for space-time foam, in which bosonic open-string states, such as photons, can possess quantum-gravity-induced velocity fluctuations in vacuum. We argue that the suggestion of light speed variation with lower bound from gamma-ray burst photon time delays can serve as a support for this string-inspired framework, through connecting the experimental finding with model predictions. We also derive the value of the effective quantum-gravity mass in this framework, and give a qualitative study on the model-dependent coefficients. Constraints from birefringent effects and/or photon decays, including the novel $\gamma$-decay constraint obtained here from the latest Tibet AS$\gamma$ near-PeV photon, are also found to be consistent with predictions in such a quantum-gravity scheme. Future observation that can testify further the theory is suggested.