Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Solution of the Strong CP problem in the low energy effective Standard
  Model   We consider the low energy effective chiral theory of QCD mesons and the
electroweak Goldstone bosons. In this effective theory the pion sector
contributes to the gauge boson masses and the Yukawa couplings of the fermions.
Consequently the Yukawa sector of quarks and leptons can have a $SU(2)_L\times
U(1)_Y\times U(1)_A$ global symmetry even with nonvanishing fermion masses. The
extra chiral $U(1)_A$ symmetry can be used to rotate the CP violating $\bar
\theta G\tilde G $ term away which therefore makes no contribution to low
energy CP violating effects like the neutron electric dipole momment. The
Goldstone mode associated with this $U(1)_A$ symmetry may be identified with
the $SU(2)$ singlet meson $\eta_0$.

17
The categories of this paper are: q-fin
10
The categories of this paper are: q-bio
22
The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
14
The categories of this paper are: math-ph
4
The categories of this paper are: cond-mat
11
The categories of this paper are: hep-lat
13
The categories of this paper are: quant-ph
19
The categories of this paper are: eess
31
The categories of this paper are: ao-sci
3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an