59 research outputs found
Infrared behavior of the running coupling constant and quarkonium spectrum
We study the effect of the infrared behavior of the running coupling constant
on the quark-antiquark spectrum.Comment: 3 pages. 1 figure, talk given at the 5th International Conference
"Quark Confinement and the Hadron Spectrum", September 10-14, 2002. Gargnano
sul Garda (BS) Ital
B_{c} meson and the light-heavy quarkonium spectrum
We compute the c \bar{b} spectrum from a first principle Salpeter equation
obtained in a preceding paper. For comparison we report also the heavy-light
quarkonium spectrum and the hyperfine separations previously presented only in
a graphical form. Notice that all results are parameter free.Comment: 7 pages. Minor changes; references added. Accepted for publication on
Phys. Rev.
Running coupling constant and masses in QCD, the meson spectrum
In line with some previous works, we study in this paper the meson spectrum
in the framework of a second order quark-antiquark Bethe-Salpeter formalism
which includes confinement. An analytic one loop running coupling constant
alpha_s(Q), as proposed by Shirkov and Sovlovtsov, is used in the calculations.
As for the quark masses, the case of a purely phenomenological running mass for
the light quarks in terms of the c. m. momentum is further investigated.
Alternatively a more fundamental expression m_P(Q) is introduced for light and
strange quarks, combining renormalization group and analyticity requirements
with an approximate solution of the Dyson-Schwinger equation. The use of such
running coupling constant and masses turns out to be essential for a correct
reproduction of the the light pseudoscalar mesons.Comment: 10 pages, 2 figures, conference: Quark Confinement and the Hadron
Spectrum VI, Villasimius, Cagliari, Ital
QCD coupling below 1 GeV from quarkonium spectrum
In this paper we extend the work synthetically presented in Ref.[1] and give
theoretical details and complete tables of numerical results. We exploit
calculations within a Bethe-Salpeter (BS) formalism adjusted for QCD, in order
to extract an ``experimental'' strong coupling \alpha_s^{exp}(Q^2) below 1 GeV
by comparison with the meson spectrum. The BS potential follows from a proper
ansatz on the Wilson loop to encode confinement and is the sum of a
one-gluon-exchange and a confinement terms. Besides, the common perturbative
strong coupling is replaced by the ghost-free expression \alpha_E(Q^2)
according to the prescription of Analytic Perturbation Theory (APT). The
agreement of \alpha_s^{exp}(Q^2) with the APT coupling \alpha_E(Q^2) turns out
to be reasonable from 1 GeV down to the 200 MeV scale, thus confirming
quantitatively the validity of the APT prescription. Below this scale, the
experimental points could give a hint on the vanishing of \alpha_s(Q^2) as Q
approaches zero. This infrared behaviour would be consistent with some lattice
results and a ``massive'' generalization of the APT approach. As a main result,
we claim that the combined BS-APT theoretical scheme provides us with a rather
satisfactory correlated understanding of very high and rather low energy
phenomena from few hundreds MeV to few hundreds GeV.Comment: Preliminary revision. Typos corrected, comments and references adde
Regge trajectories and quarkonium spectrum from a first principle Salpeter equation
We compute the heavy-heavy, light-light and light-heavy quarkonium spectrum
starting from a first principle Salpeter equation obtained in a preceding
paper. We neglect spin-orbit structures and exclude from our treatment the
light pseudoscalar states which in principle would require the use of the full
Bethe-Salpeter equation due to the chiral symmetry breaking problem. For the
rest we find an overall good agreement with the experimental data. In
particular for the light-light case we find straight Regge trajectories with
the right slope and intercepts. The strong coupling constant , the
string tension occurring in the potential and the heavy quark masses
are taken from the heavy quarkonium semirelativistic fit with only a small
rearrangement. The light quark masses are set equal to baricentral value of the
current quark masses as reported by the particle data group. For what concerns
the light-light and the light-heavy systems the calculation is essentially
parameter free.Comment: 18 pages, 3 figures, revtex.st
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