Revisiting light propagation over (loop) quantum Universe

TL;DR

This paper investigates electromagnetic wave propagation in a quantum cosmological setting, demonstrating that loop quantum effects do not cause superluminal speeds and instead suppress dispersion modifications at low energies.

Contribution

It provides a systematic analysis showing that loop quantum cosmology aligns with general relativity at low energies and reduces dispersion relation modifications compared to geometrodynamics.

Findings

Electromagnetic waves follow general relativity predictions at low energies.

Loop quantum effects suppress dispersion relation modifications.

No superluminal propagation observed in the model.

Abstract

One of the principal aspects through which the effects of quantum gravity are hoped to manifest is the possible modification of the dispersion relation for electromagnetic (e-m) waves. By combining (i) the symmetry reduced approaches to spacetime quantization, including loop quantum cosmology or geometrodynamics framework, and (ii) the (extension of the) Born-Oppenheimer approximation of interacting fields, one can build a reliable though still quasi-phenomenological model for a description of propagation of the e-m radiation over a cosmological spacetime. The past works employing such approach indicated a pathological behavior - superluminal propagation at low energies. We reexamine the approach via systematic studies (using indicated method) of e-m wave propagation over a flat quantum Friedmann-Lemaitre-Robertson-Walker Universe using a synthesis of analytical and numerical methods. It turns out, that (i) the e-m wave propagation agrees with the one predicted by general relativity in the low energy limit, and (ii) loop quantum effects actually suppress the modifications to the dispersion relation in comparison with those predicted, where the geometry is quantized via geometrodynamics.