Derivation of a Vacuum Refractive Index in a Stringy Space-Time Foam Model
By John Ellis, N. Mavromatos, D. Nanopoulos. 2008
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Abstract It has been suggested that energetic photons propagating in vacuo should experience a non-trivial refractive index due to the foamy structure of space–time induced by quantum-gravitational fluctuations. The sensitivity of recent astrophysical observations, particularly of AGN Mk501 by the MAGIC Collaboration, approaches the Planck scale for a refractive index depending linearly on the photon energy. We present here a new derivation of this quantum-gravitational vacuum refraction index, based on a stringy analogue of the interaction of a photon with internal degrees of freedom in a conventional medium. We model the space–time foam as a gas of D-particles in the bulk space–time of a higher-dimensional cosmology where the observable Universe is a D3-brane. The interaction of an open string representing a photon with a D-particle stretches and excites the string, which subsequently decays and re-emits the photon with a time delay that increases linearly with the photon energy and is related to stringy uncertainty principles. We relate this derivation to other descriptions of the quantum-gravitational refractive index in vacuo .
Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics, Statistical and Nonlinear Physics
View Paper: https://www.semanticscholar.org/paper/7988119df58739eb439c7ed9abcba1148f25f30d
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- Dark matter and fundamental physics with the Cherenkov Telescope Array (2012, background): “For example there are specific predictions in some toy models [161,162] and a general parameterisation can be provided in the framework of effective field theory [159].”