Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Naturally light invisible axion in models with large local discrete
  symmetries   We show that by introducing appropriate local $Z_N(N\geq13)$ symmetries in
electroweak models it is possible to implement an automatic Peccei-Quinn
symmetry keeping at the same time the axion protected against gravitational
effects. Although we consider here only an extension of the standard model and
a particular 3-3-1 model, the strategy can be used in any kind of electroweak
model. An interesting feature of this 3-3-1 model is that if: {\it i)} we add
right-handed neutrinos, {\it ii)} the conservation of the total lepton number,
and {\it iii)} a $Z_2$ symmetry, the $Z_{13}$ and the chiral Peccei-Quinn
$U(1)_{\rm PQ}$ are both accidental symmetries in the sense that they are not
imposed on the Lagrangian but they are just the consequence of the particle
content of the model, its gauge invariance, renormalizability and Lorentz
invariance. In addition, this model has no domain wall problem.

15
The categories of this paper are: nucl-ex
36
The categories of this paper are: cmp-lg
31
The categories of this paper are: ao-sci
10
The categories of this paper are: q-bio
22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
26
The categories of this paper are: bayes-an
4
The categories of this paper are: cond-mat
8
The categories of this paper are: hep-ex
18
The categories of this paper are: econ
12
The categories of this paper are: nucl-th
3
The categories of this paper are: physics
27
The categories of this paper are: comp-gas
2
The categories of this paper are: math
13
The categories of this paper are: quant-ph
1
The categories of this paper are: cs