Spacetime foam, CPT anomaly, and photon propagation

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  • 2 December 2003
Abstract
The CPT anomaly of chiral gauge theories has been established previously for multiply connected spacetime manifolds M of the type R^3 x S^1, where the noncontractible loops can be said to wrap around the whole universe. In this paper, we show that the CPT anomaly also occurs for manifolds where the noncontractible loops can be arbitrarily small. Our basic calculation is performed for a noncompact manifold with a single "puncture," namely M = R^2 x (R^2 {0}). A hypothetical spacetime foam might have many such punctures. Assuming the multiply connected structure of the foam to be time independent, we present a simple model for photon propagation, which generalizes the single-puncture result. This model leads to a modified dispersion law of the photon. Observations of high-energy photons (gamma-rays) from explosive extragalactic events can then be used to place an upper bound on the typical length scale of these frozen-in punctures.

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