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

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 $\alpha_s$, the string tension $\sigma$ 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

Analytic perturbation theory versus 1/N expansion in the Gross-Neveu model

The 1/N expansion can be successfully used to calculate the Green functions of the two-dimensional O(2N) Gross - Neveu model. In parallel, the methods of analytic perturbation theory are also applied. Comparing the results of these two calculations at leading order, we report on the surprising agreement between them.Comment: Latex, 3 figures, 4 page