Quantum Lightcone Fluctuations in Compactified Spacetimes

TL;DR

This paper investigates how compactified extra spatial dimensions influence light propagation in linearized quantum gravity, revealing small but potentially observable effects on pulse flight times and spectral line widths.

Contribution

It provides a detailed analysis of lightcone fluctuations caused by compactified dimensions, including growth of flight time variations and line narrowing effects.

Findings

Flight time fluctuations grow logarithmically with distance in Kaluza-Klein models.

Compactification causes small spectral line narrowing effects.

Effects are too small for current detection but could test extra dimensions.

Abstract

We treat the effects of compactified spatial dimensions on the propagation of light in the uncompactified directions in the context of linearized quantum gravity. We find that the flight times of pulses can fluctuate due to modification of the graviton vacuum by the compactification. In the case of a five dimensional Kaluza-Klein theory, the mean variation in flight time can grow logarithmically with the flight distance. This effect is in principle observable, but too small to serve as a realistic probe of the existence of extra dimensions. We also examine the effect of the compactification on the widths of spectral lines, and find that there is a small line narrowing effect. This effect is also small for compactification well above the Planck scale, but might serve as a test of the existence of extra dimensions.