Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: CP violation in QCD   Among the parameters of QCD is one that results in CP violation when
non-vanishing. This is closely related to possible quark mass terms. It is
conventionally interpreted in terms of gauge field topology or alternatively in
terms of phases in the quark masses. There is no experimental evidence for this
parameter having a non-zero value, a puzzle for theories involving unification.

7
The categories of this paper are: hep-th
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
29
The categories of this paper are: funct-an
26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
4
The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci
25
The categories of this paper are: patt-sol
5
The categories of this paper are: gr-qc
27
The categories of this paper are: comp-gas
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
6
The categories of this paper are: astro-ph