Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quantum gravitational optics: Effective Raychaudhuri equation   Vacuum polarization in QED in a background gravitational field induces
interactions which {\it effectively} modify the classical picture of light
rays, as the null geodesics of spacetime. These interactions violate the strong
equivalence principle and affect the propagation of light leading to
superluminal photon velocities. Taking into account the QED vacuum
polarization, we study the propagation of a bundle of rays in a background
gravitational field. To do so we consider the perturbative deformation of
Raychaudhuri equation through the influence of vacuum polarization on photon
propagation. We analyze the contribution of the above interactions to the
optical scalars namely, shear, vorticity and expansion using the Newman-Penrose
formalism.

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The categories of this paper are: plasm-ph
23
The categories of this paper are: solv-int
29
The categories of this paper are: funct-an
8
The categories of this paper are: hep-ex
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
21
The categories of this paper are: adap-org
3
The categories of this paper are: physics
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
18
The categories of this paper are: econ