Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Interpreting the Recent Upper Limit on the Gravitational Wave Background
  from the Parkes Pulsar Timing Array   We provide comments on the article by Shannon et al. (Sep 2015) entitled
"Gravitational waves from binary supermassive black holes missing in pulsar
observations". The purpose of this letter is to address several misconceptions
of the public and other scientists regarding the conclusions of that work.

16
The categories of this paper are: stat
19
The categories of this paper are: eess
1
The categories of this paper are: cs
4
The categories of this paper are: cond-mat
13
The categories of this paper are: quant-ph
9
The categories of this paper are: nlin
27
The categories of this paper are: comp-gas
7
The categories of this paper are: hep-th
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
32
The categories of this paper are: atom-ph
28
The categories of this paper are: alg-geom
20
The categories of this paper are: acc-phys
15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
29
The categories of this paper are: funct-an