We present new results of a relativistic quark model based on the Bethe-Salpeter equation in its instantaneous approximation. Assuming a linearly rising confinement potential with an appropriate spinorial structure in Dirac space and adopting a residual interaction based on instanton effects, we can compute masses of the light mesons up to highest observed angular momenta with a natural solution of the UA(1) problem. The calculated ground states masses and the radial excitations describe the experimental results well. In this paper, we will also discuss our results concerning numerous meson decay properties. For processes like π + /K + → e + νeγ and 0 − → γγ at various photon virtualities, we find a good agreement with experimental data. We will also comment on the form factors of the K 3 decay and on the decay constants of the π, K and η mesons. For the sake of completeness, we will furthermore present the electromagnetic form factors of the charged π and K mesons as well as a comparison of the radiative meson decay widths with the most recent experimental data.

Within the framework of the instantaneous Bethe-Salpeter equation, we present a detailed analysis of light meson spectra with respect to various parameterizations of confinement in Dirac space. Assuming a linearly rising quark-antiquark potential, we investigate two different spinorial forms (Dirac structures), namely 1 2 (1 I⊗1 I−γ 0 ⊗γ 0 ) as well as the UA(1)-invariant combination 1 2 (1 I⊗1 I−γ 5 ⊗ γ 5 − γ µ ⊗ γµ), both providing a good description of the ground state Regge trajectories up to highest observed angular momenta. Whereas the first structure is slightly prefered concerning numerous meson decay properties (see [41]), we find the UA(1)-invariant force to be much more appropriate for the description of a multitude of higher mass resonances discovered in the data of the Crystal Barrel collaboration during the last few years. Furthermore, this confinement structure has the remarkable feature to yield a linear dependence of masses on their radial excitation number. For many experimental resonances such a trajectory-like behaviour was observed by Anisovich et al. We can confirm that almost the same slope occurs for all trajectories. Adding the UA(1)-breaking instanton induced 't Hooft interaction we can compute the pseudoscalar mass splittings with both Dirac structures and for the scalar mesons a natural mechanism of flavour mixing is achieved. In the scalar sector, the two models provide completely different ground state and excitation masses, thus leading to different assignments of possibleqq states in this region. The scalar meson masses calculated with the structure 1 2 (1 I ⊗ 1 I − γ 5 ⊗ γ 5 − γ µ ⊗ γµ) are in excellent agreement with the K-matrix poles deduced from experiment by Anisovich and coworkers. *

No abstract

In this paper, we present results on strong two-body decay widths of light qq mesons calculated in a covariant quark model. The model is based on the Bethe-Salpeter equation in its instantaneous approximation and has already been used for computing the complete meson mass spectrum and many electroweak decay observables. Our approach relies on the use of a phenomenological confinement potential with an appropriate spinorial Dirac structure and 't Hooft's instantoninduced interaction as a residual force for pseudoscalar and scalar mesons.The transition matrix element for the decay of one initial meson into two final mesons is evaluated in lowest order by considering conventional decays via quark loops as well as Zweig rule violating instanton-induced decays generated by the six-quark vertex of 't Hooft's interaction; the latter mechanism only contributes if all mesons in the decay have zero total angular momentum. We show that the interference of both decay mechanisms plays an important role in the description of the partial widths of scalar and pseudoscalar mesons. 1 Note that a recent preprint by Barnes et al. (see [39]) also investigates the non-nn meson decays; we comment on this work in section 4.

In this paper we investigate weak decays of heavy mesons in the framework of a covariant quark model, which is based on the Bethe-Salpeter equation in instantaneous approximation. Apart from a phenomenological confinement potential, a residual interaction induced by instantons is adopted. Masses and many decay observables of light mesons have already been described successfully in this model [4,5]. An appropiate extension allows a unified description of light and heavy systems. Using a set of parameters which are fixed by the mass spectra, we evaluate the form factors of semileptonic decays of charmed and bottom mesons. In the heavy quark limit these can be reduced to the Isgur-Wise function, which is calculated. Finally the form factors are used to determine the non-leptonic decay rates of B mesons in the factorization approximation.1 For a similar investigation of weak meson decays in the Bethe Salpeter framework with the One Gluon Exchange see [7].