Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Calculation of axion-photon-photon coupling in string theory   The axion search experiments invite a plausible estimation of the
axion--photon--photon coupling constant $\overline{c}_{a\gamma\gamma}$ in
string models with phenomenologically acceptable visible sectors. We present
the calculation of $\overline{c}_{a\gamma\gamma}$ with an exact Peccei-Quinn
symmetry. In the Huh-Kim-Kyae $\Z_{12-I}$ orbifold compactification, we obtain
$\overline{c}_{a\gamma\gamma} =\frac{8}{3}$ even with a lot of singlets at the
GUT scale, and the low-temperature axion search experiments will probe the QCD
corrected coupling, $ {c}_{a\gamma\gamma} \simeq
\overline{c}_{a\gamma\gamma}-1.98\simeq 0.69$.

34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess
11
The categories of this paper are: hep-lat
20
The categories of this paper are: acc-phys
21
The categories of this paper are: adap-org
5
The categories of this paper are: gr-qc
1
The categories of this paper are: cs
3
The categories of this paper are: physics
18
The categories of this paper are: econ
29
The categories of this paper are: funct-an
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
30
The categories of this paper are: q-alg
12
The categories of this paper are: nucl-th
8
The categories of this paper are: hep-ex