Space-Time Foam may Violate the Principle of Equivalence

TL;DR

This paper explores how quantum gravity-induced space-time foam could lead to violations of Lorentz invariance and the equivalence principle, especially affecting uncharged particles like photons, with implications for quantum gravity phenomenology.

Contribution

It presents two models based on D-particle fluctuations showing potential Lorentz invariance violations for certain energetic particles, highlighting non-universality in particle interactions with space-time foam.

Findings

Photons may violate Lorentz invariance due to space-time foam effects.

Charged particles like electrons remain Lorentz-invariant in these models.

Gluons might violate Lorentz invariance, neutrinos likely do not.

Abstract

The interactions of different particle species with the foamy space-time fluctuations expected in quantum gravity theories may not be universal, in which case different types of energetic particles may violate Lorentz invariance by varying amounts, violating the equivalence principle. We illustrate this possibility in two different models of space-time foam based on D-particle fluctuations in either flat Minkowski space or a stack of intersecting D-branes. Both models suggest that Lorentz invariance could be violated for energetic particles that do not carry conserved charges, such as photons, whereas charged particles such electrons would propagate in a Lorentz-inavariant way. The D-brane model further suggests that gluon propagation might violate Lorentz invariance, but not neutrinos. We argue that these conclusions hold at both the tree (lowest-genus) and loop (higher-genus) levels, and discuss their implications for the phenomenology of quantum gravity.