Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Light mesons and infrared behavior of the running coupling constant in
  QCD   A previous method for handling bound states in QCD is briefly revisited.
Taking advantage of the Feynman-Schwinger representation for the iterated quark
propagator in an external field, it is possible to give closed representations
for certain appropriate (second order) two point and four point Green
functions, H^(2)(x-y) and H^(4)(x_1,x_2,y_1,y_2), as path integrals on quark
world lines. Then, starting from reasonable assumptions on the Wilson line
correlators, a Bethe-Salpeter equation for H^(4) and a Dyson-Schwinger equation
for H^(2) can be obtained, which are consistent with the Goldstone theorem in
the chiral limit. Such equations are too complicate to be solved directly.
However, a reduced Salpeter equation can be derived which is tractable and has
been applied to a calculation of the meson spectrum. The results are in general
good agreement with the data, but with the important exceptions of the light
pseudo scalars (that are related to the breaking of the chiral symmetry). In
this scenario two important improvements can be introduced: a) the fixed
coupling constant can be replaced by a running coupling constant
\alpha_{s}(Q^2) appropriately modified in the infrared region; b) the fixed
mass in the reduced equation can be replaced for light quarks by an effective
mass depending on the momentum of the particle, as suggested by the form of the
DS equation. Then even the light pseudo scalar mesons can be made to agree with
to their experimental value.

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The categories of this paper are: physics
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The categories of this paper are: math
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-lat
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The categories of this paper are: gr-qc
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The categories of this paper are: q-fin
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The categories of this paper are: hep-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: eess
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The categories of this paper are: patt-sol
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The categories of this paper are: chem-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: econ
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The categories of this paper are: adap-org
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The categories of this paper are: supr-con