Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Astrophysical limits on quantum gravity motivated birefringence   We obtain observational upper bounds on a class of quantum gravity related
birefringence effects, by analyzing the presence of linear polarization in the
optical and ultraviolet spectrum of some distant sources. In the notation of
Gambini and Pullin we find $\chi < 10^{-3}$.

35
The categories of this paper are: mtrl-th
9
The categories of this paper are: nlin
8
The categories of this paper are: hep-ex
6
The categories of this paper are: astro-ph
29
The categories of this paper are: funct-an
13
The categories of this paper are: quant-ph
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
0
The categories of this paper are: hep-ph
7
The categories of this paper are: hep-th
27
The categories of this paper are: comp-gas
16
The categories of this paper are: stat
14
The categories of this paper are: math-ph
10
The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat
26
The categories of this paper are: bayes-an