Probing Models of Quantum Space-Time Foam

TL;DR

This paper explores how quantum fluctuations at the Planck scale, modeled via string theory and D-brane recoil, could cause observable effects like energy-dependent light speed variations, testable through astrophysical observations.

Contribution

It introduces a string-inspired model of space-time foam incorporating D-brane recoil effects, predicting energy-dependent metric perturbations and potential observational signatures.

Findings

D-brane recoil induces an energy-dependent refractive index in vacuum.

Astrophysical sources like GRBs can test space-time foam effects.

The model suggests possible cosmological vacuum energy dynamics.

Abstract

We review the possibility that quantum fluctuations in the structure of space-time at the Planck scale might be subject to experimental probes. We study the effects of space-time foam in an approach inspired by string theory, in which solitonic D-brane excitations are taken into account when considering the ground state. We model the properties of this medium by analyzing the recoil of a D particle which is induced by the scattering of a closed-string state. We find that this recoil causes an energy-dependent perturbation of the background metric, which in turn induces an energy-dependent refractive index in vacuo, and stochastic fluctuations of the light cone. We show how distant astrophysical sources such as Gamma-Ray Bursters (GRBs) may be used to test this possibility, making an illustrative analysis of GRBs whose redshifts have been measured. Within this framework, we also discuss the propagation of massive particles and the possible appearance of cosmological vacuum energy that relaxes towards zero. We also discuss D-brane recoil in models with `large' extra dimensions.