Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: String Junction Model, Cluster Hypothesis, Penta-Quark Baryon and
  Tetra-Quark Meson   Thirty years ago we proposed string junction model of hadrons and examined
structure and reaction of hadrons including exotic ones. Mass $m$ of exotic
hadrons of light quarks is roughly given by $m \sim N_J\cdot m_B$, where $N_J$
is the total number of junctions and $m_B \sim 1$ GeV is the ordinary light
baryon mass. In this paper we introduce "cluster hypothesis" into the model by
which mass of a complex hadron is given by the sum of masses of clusters
composing it. The hypothesis guarantees the established picture that mass
differences of hadrons of the same string junction structure are due to those
of the constituent quarks. A candidate for penta-quark baryon $\Theta$(1530
MeV, $S=+1)$ including a strange anti-quark ${\sb}$ and that for tetra-quark
meson $Z^+$(4430 MeV) recently reported by the Bell collaboration are examined
in parallel. $\Theta $ is considered to have non-strange partners, which are
lighter by the mass difference $\Delta_s$ between strange and non-strange
quarks. Mass of such light penta-quark baryons with $N_J=3$ is expected to be
about 3 GeV. Several parameters of the model are estimated such as mass of
junction of $m_J \sim O(10)$ MeV. While mass of light tetra-quark meson with
$N_J=2$ is expected to be about 2 GeV, $Z^+$(4430 MeV) containing
$(u,c,{\db},{\cb})$ gives a clue to determine some parameters of the model,
e.g., inter-junction string energy $m_{IJ}$.

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The categories of this paper are: math-ph
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The categories of this paper are: q-bio
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The categories of this paper are: econ
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The categories of this paper are: q-alg
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The categories of this paper are: cmp-lg
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The categories of this paper are: plasm-ph
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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: stat
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The categories of this paper are: solv-int
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The categories of this paper are: eess
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The categories of this paper are: q-fin
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The categories of this paper are: gr-qc
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The categories of this paper are: comp-gas
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The categories of this paper are: math
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The categories of this paper are: astro-ph