Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Derivation of a Vacuum Refractive Index in a Stringy Space-Time Foam
  Model   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.

22
The categories of this paper are: chao-dyn
10
The categories of this paper are: q-bio
35
The categories of this paper are: mtrl-th
37
The categories of this paper are: supr-con
2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
28
The categories of this paper are: alg-geom
1
The categories of this paper are: cs
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol
32
The categories of this paper are: atom-ph