Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Two-Photon Decays of Mesons in a Relativistic Quark Model   We present a relativistic calculation of two-photon decays for heavy and
light mesons in the framework of the Salpeter equation for quark-antiquark
states. The meson-photon-photon vertex is computed by reconstructing the
Bethe-Salpeter vertex function and evaluating the four-dimensional Feynman
diagram with off-shell quark amplitudes. The two-photon width for light and
heavy quarkonia up to spin equal six are calculated with different parameter
sets taken from the literature thus giving a complete overview on the mesonic
two-photon physics. We find that relativistic effects including the negative
energy components of the wave function are important for any two-photon width -
even for heavy quarkonia - yielding a remarkable agreement with available data.

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The categories of this paper are: chao-dyn
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The categories of this paper are: patt-sol
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The categories of this paper are: nucl-ex
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The categories of this paper are: eess
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The categories of this paper are: econ
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The categories of this paper are: stat
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The categories of this paper are: hep-th
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The categories of this paper are: q-alg
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The categories of this paper are: plasm-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: gr-qc
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The categories of this paper are: funct-an
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The categories of this paper are: alg-geom
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The categories of this paper are: chem-ph
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The categories of this paper are: q-bio
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The categories of this paper are: ao-sci