Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A perturbative approach to the eta_c-gamma transition form factor   The eta_c-gamma transition form factor is calculated within a perturbative
approach. For the eta_c-meson, a wave function of the Bauer-Stech-Wirbel type
is used where the two free parameters, namely the decay constant f(eta_c) and
the transverse size of the wave function, are related to the Fock state
probability and the width for the two-photon decay Gamma[eta_c -> gamma gamma].
The Q^2 dependence of the eta_c-gamma transition form factor is well
determined.

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The categories of this paper are: hep-th
29
The categories of this paper are: funct-an
11
The categories of this paper are: hep-lat
26
The categories of this paper are: bayes-an
28
The categories of this paper are: alg-geom
5
The categories of this paper are: gr-qc
18
The categories of this paper are: econ
30
The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: chao-dyn
3
The categories of this paper are: physics
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
31
The categories of this paper are: ao-sci
1
The categories of this paper are: cs