Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Observation of polarized stochastic gravitational-wave background in
  pulsar-timing-array experiments
28
The categories of this paper are: alg-geom
29
The categories of this paper are: funct-an
18
The categories of this paper are: econ
35
The categories of this paper are: mtrl-th
19
The categories of this paper are: eess
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
34
The categories of this paper are: chem-ph
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol
36
The categories of this paper are: cmp-lg
26
The categories of this paper are: bayes-an
3
The categories of this paper are: physics
1
The categories of this paper are: cs
7
The categories of this paper are: hep-th