Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Time Delays of Strings in D-particle Backgrounds and Vacuum Refractive
  Indices   Using standard techniques in string/D-brane scattering amplitude
computations, we evaluate the scattering of open strings off D-particles in
brane world scenarios. The D-particles are viewed as D3 branes wrapped up
around three cycles, and their embedding in brane worlds constitutes a case of
intersecting branes, among which strings are stretched, representing various
types of excitations of the Standard Model (SM) particles in the low-energy
limit. Our analysis, reveals interesting and novel selection rules for the
resulting causal time delays, proportional to the energy of the incident matter
state, from the processes of splitting, capture and re-emission of the latter
by the D-particles. In particular, we show that there are relatively large time
delays only for excitations that belong to the Cartan subalgebra of the SM
gauge group, which notably includes photons. We discuss the possible relevance
of these results to the models of space time foam predicting a non-trivial
vacuum refractive index for photons and the associated cosmic \gamma-ray
phenomenology. In particular, we demonstrate how low-string-scale models can be
falsified already in this context, by current astrophysical observations of
cosmic photons, and how such observations serve as a way to discriminate low-
from high-string scale models.

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The categories of this paper are: econ
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The categories of this paper are: cond-mat
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The categories of this paper are: q-bio
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-lat
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The categories of this paper are: supr-con
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The categories of this paper are: math-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: q-alg
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The categories of this paper are: solv-int
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-ex
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The categories of this paper are: chao-dyn
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The categories of this paper are: acc-phys
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The categories of this paper are: nlin
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The categories of this paper are: quant-ph