Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Anomalous solutions to the strong CP problem   We present a new mechanism for solving the strong CP problem using a Z2
discrete symmetry and an anomalous U(1) symmetry. A Z2 symmetry is used so that
two gauge groups have the same theta angle. An anomalous U(1) symmetry makes
the difference between the two theta angles physical and the sum unphysical.
Two models are presented where the anomalous symmetry manifests itself in the
IR in different ways. In the first model there are massless bifundamental
quarks, a solution reminiscent of the massless up quark solution. In the IR of
this model, the $\eta'$ boson relaxes the QCD theta angle to the difference
between the two theta angles - in this case zero. In the second model, the
anomalous U(1) symmetry is realized in the IR as a dynamically generated mass
term that has exactly the phase needed to cancel the theta angle. Both of these
models make the extremely concrete prediction that there exist new colored
particles at the TeV scale.

4
The categories of this paper are: cond-mat
21
The categories of this paper are: adap-org
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
22
The categories of this paper are: chao-dyn
32
The categories of this paper are: atom-ph
31
The categories of this paper are: ao-sci
1
The categories of this paper are: cs
11
The categories of this paper are: hep-lat
18
The categories of this paper are: econ
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg