Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Lorentz violation induced vacuum birefringence and its astrophysical
  consequences   In the electromagnetism of loop quantum gravity, two helicities of a photon
have different phase velocities and group velocities, termed as "vacuum
birefringence". Two novel phenomenons, "peak doubling" and "de-polarization",
are expected to appear for a linearly polarized light from astrophysical
sources. We show that the criteria to observe these two phenomenons are the
same. Further, from recently observed $\gamma$-ray polarization from Cygnus
X-1, we obtain an upper limit $\sim 8.7\times10^{-12}$ for Lorentz-violating
parameter $\chi$, which is the most firm constraint from well-known systems. We
also suggest to analyze possible existence of "peak doubling" through Fermi LAT
GRBs.

29
The categories of this paper are: funct-an
32
The categories of this paper are: atom-ph
34
The categories of this paper are: chem-ph
33
The categories of this paper are: plasm-ph
2
The categories of this paper are: math
4
The categories of this paper are: cond-mat
26
The categories of this paper are: bayes-an
9
The categories of this paper are: nlin
13
The categories of this paper are: quant-ph
20
The categories of this paper are: acc-phys
28
The categories of this paper are: alg-geom
5
The categories of this paper are: gr-qc
17
The categories of this paper are: q-fin
11
The categories of this paper are: hep-lat
15
The categories of this paper are: nucl-ex
22
The categories of this paper are: chao-dyn