Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Meson Spectrum in a Covariant Quark Model   Within the framework of the instantaneous Bethe-Salpeter equation, we present
a detailed analysis of light meson spectra with respect to various
parameterizations of confinement in Dirac space. Assuming a linearly rising
quark-antiquark potential, we investigate two different spinorial forms (Dirac
structures), namely ${1/2}(\Id\otimes\Id - \gamma^0\otimes\gamma^0)$ as well as
the $U_A(1)$-invariant combination ${1/2}(\Id\otimes\Id -
\gamma^5\otimes\gamma^5 - \gamma^\mu\otimes\gamma_\mu)$, both providing a good
description of the ground state Regge trajectories up to highest observed
angular momenta. Whereas the first structure is slightly prefered concerning
numerous meson decay properties (see \cite{pap41}), we find the
$U_A(1)$-invariant force to be much more appropriate for the description of a
multitude of higher mass resonances discovered in the data of the {\sc Crystal
Barrel} collaboration during the last few years. Furthermore, this confinement
structure has the remarkable feature to yield a linear dependence of masses on
their radial excitation number. For many experimental resonances such a
trajectory-like behaviour was observed by Anisovich {\it et al.} We can confirm
that almost the same slope occurs for all trajectories. Adding the
$U_A(1)$-breaking instanton induced 't Hooft interaction we can compute the
pseudoscalar mass splittings with both Dirac structures and for the scalar
mesons a natural mechanism of flavour mixing is achieved. [...]

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The categories of this paper are: astro-ph
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The categories of this paper are: eess
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The categories of this paper are: mtrl-th
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The categories of this paper are: adap-org
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The categories of this paper are: hep-th
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The categories of this paper are: stat
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The categories of this paper are: alg-geom
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The categories of this paper are: funct-an
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The categories of this paper are: ao-sci
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The categories of this paper are: bayes-an
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The categories of this paper are: nucl-ex
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The categories of this paper are: nucl-th
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The categories of this paper are: cond-mat
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-lat