24 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
Bethe-Salpeterova i Dyson-Schwingerova jednadžba i Wilsonova petlja u QCD, učinkovit operator mase i qq¯ spektar
We briefly discuss the quark-antiquark Bethe-Salpeter equation and the quark Dyson-Schwinger equation derived in preceding papers. We also consider the qq¯ quadratic mass operator M2 = (w1 + w2) 2 + U obtained by a three-dimensional reduction of the BS equation and the related approximate centre-of-mass Hamiltonian or linear-mass-operator HCM ≡ M = w1 + w2 + V + .... We review previous results on the spectrum and the Regge trajectories obtained by an approximate diagonalization of HCM and report new results similarly obtained for the original M2 . We show that in both cases we succeed to reproduce fairly well the entire meson spectrum in the cases in which the numerical calculations were actually practicable and with the exception of the light pseudoscalar states (related to the chiral symmetry problematic). A small rearrangement of the parameters and the use of a running coupling constant is necessary in the M2 case.Kratko se raspravlja Bethe-Salpeterova jednadžba za sustav kvark-antikvark i Dyson-Schwingerova jednadžba za kvarkove koje su ranije izvedene, qq¯ kvadratični operator mase M2 = (w1 + w2) 2 + U koji je izveden iz BS jednadžbe te približna Hamiltonova funkcija za centar mase odnosno linearni operator mase HCM ≡ M = w1 + w2 + V + .... Izlažu se raniji ishodi računa za spektar mezona i Reggeove putanje koji su dobiveni približnom dijagonalizacijom HCM, te navode novi ishodi koji su slično postignuti za izvorni M2 . Pokazuje se kako se u oba slučaja prilično dobro postiže cjelokupan spektar mezona za slučajeve kada su numerički računi provedivi i uz isključenje lakih pseudoskalarnih stanja (povezanih s problematikom kiralne simetrije). U slučaju M2 potrebna su mala podešavanja parametara i jedna stalnica vezanja
Bound state approach to the QCD coupling at low energy scales
We exploit theoretical results on the meson spectrum within the framework of
a Bethe-Salpeter (BS) formalism adjusted for QCD, in order to extract an
``experimental'' coupling \alpha_s^{exp}(Q^2) below 1 GeV by comparison with
the data. Our results for \alpha_s^{exp}(Q^2) exhibit a good agreement with the
infrared safe Analytic Perturbation Theory (APT) coupling from 1 GeV down to
200 MeV. 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 low energy phenomena.Comment: Revised version, to appear on Physical Review Letters. 7 pages, 2
figures, Revte