Instanton Effects in the Decay of Scalar Mesons

We show that instanton effects may play a crucial role in the decay of scalar mesons into two pseudoscalars. Particularly the branching ratios of two meson decays of the $f_0(1500)$, which is considered as a glue-ball candidate, are then compatible with an ordinary $q \bar{q}$-structure of this resonance and a small positive SU(3) mixing angle, close to a result recently calculated with the same instanton-induced force.Comment: 9 pages, uuencoded latex including two figure

Analysis of the instantaneous Bethe-Salpeter equation for qqˉq\bar{q}-bound-states

We investigate the structure of the instantaneous Bethe-Salpeter equation for $q\bar{q}$-bound states in the general case of unequal quark masses and develop a numerical scheme for the calculation of mass spectra and Bethe-Salpeter amplitudes. In order to appreciate the merits of the various competing models beyond the reproduction of the mass spectra we present explicit formulas to calculate electroweak decays. The results for an explicit quark model will be compared to experimental data in a subsequent paperComment: 11 pages, RevTeX, TK-93-1

A Bethe-Salpeter model for light mesons: spectra and decays

The spectra and electroweak decay properties of light mesons are analyzed within the framework of the instantaneous Bethe-Salpeter equation. The interaction kernel comprises alternative spin-structures for a parameterization of confinement and a residual quark-antiquark interaction based on instanton effects. It is shown that only with a vector confinement the parameters can be chosen such as to yield an excellent description of the light pseudoscalar and vector mesons including weak and two photon decays. However it is found that it is not possible to reconcile this with the Regge behavior of higher lying meson states with the same parameter set.Comment: 12 pages, RevTeX, TK-93-1

Scalar Mesons in a Relativistic Quark Model with Instanton-Induced Forces

In a relativistic quark model with linear confinement and an instanton-induced interaction which solves the $\eta$-$\eta'$ puzzle, scalar mesons are found as almost pure SU(3) flavor states. This suggests a new interpretation of the scalar nonet: We propose that the recently discovered $f_0(1500)$ is not a glueball but the scalar (mainly)--octet meson for which the $K\bar{K}$ decay mode is suppressed. The mainly--singlet state is tentatively identified with the $f_0(980)$. The isovector and isodoublet states correspond to the $a_0(1450)$ and $K^{\ast}(1430)$, respectively.Comment: 10 pages including 2 uuencoded figures, RevTe

Study of the process e+e−→π+π−π0e^+e^- \to \pi^+\pi^-\pi^0 in the energy region s\sqrt[]{s} from 0.98 to 1.38 GeV.}

The cross section of the process $e^+e^-\to \pi^+\pi^-\pi^0$ was measured in the Spherical Neutral Detector experiment at the VEPP-2M collider in the energy region $\sqrt[]{s} = 980 \div 1380$ MeV. The measured cross section, together with the $e^+e^-\to \pi^+\pi^-\pi^0$ and $\omega\pi^+\pi^-$ cross sections obtained in other experiments, was analyzed in the framework of the generalized vector meson dominance model. It was found that the experimental data can be described by a sum of $\omega$, $\phi$ mesons and two $\omega^\prime$ and $\omega^{\prime\prime}$ resonances contributions, with masses $m_{\omega^\prime}\sim 1490$,$m_{\omega^{\prime\prime}}\sim 1790$ MeV and widths $\Gamma_{\omega^\prime}\sim 1210$, $\Gamma_{\omega^{\prime\prime}}\sim 560$ MeV. The analysis of the $\pi^+\pi^-$ invariant mass spectra in the energy region $\sqrt[]{s}$ from 1100 to 1380 MeV has shown that for their descriptionone should take into account the $e^+e^-\to\omega\pi^0\to\pi^+\pi^-\pi^0$ mechanism also. The phase between the amplitudes corresponding to the $e^+e^-\to\omega\pi$ and $e^+e^-\to\rho\pi$ intermediate states was measured for the first time. The value of the phase is close to zero and depends on energy.Comment: 29 pages REVTEX and 17 figures, accepted for publication in Physical Review

MANY-PARTICLE MANY-HOLE EXCITATIONS AND THE RETARDATION OF MAGNETIC DIPOLE AND GT TRANSITION-STRENGTHS

Les effets de structure nucléaire et subnucléaire sur les modes de spin dans les noyaux sont discutés sur trois exemples : la distribution d'intensité Gamow-Teller dans le 90Zr, l'opérateur M1 effectif, et le cas du 48Ca.Three examples of the role of nuclear and subnuclear structure effects in spin-flip modes in nuclei is discussed viz. The GT strength distribution in 90Zr, an effective M1 operator and a discussion of 48Ca

Central and noncentral components of the preedom-wildenthal interaction

The influence of the various components of the Preedom-Wildenthal interaction - viz., central, tensor, spin-orbit (LS) and antisymmetric spin-orbit (ALS) - on properties of A = 20,21 nuclei is investigated. The effects of the LS and ALS components on the one hand and of the central and tensor components on the other hand are found to be very similar. It turns out to be possible to remove the ALS component in favour of an enhanced LS component without spoiling the agreement with experiment

Central and noncentral components of the preedom-wildenthal interaction

The influence of the various components of the Preedom-Wildenthal interaction - viz., central, tensor, spin-orbit (LS) and antisymmetric spin-orbit (ALS) - on properties of A = 20,21 nuclei is investigated. The effects of the LS and ALS components on the one hand and of the central and tensor components on the other hand are found to be very similar. It turns out to be possible to remove the ALS component in favour of an enhanced LS component without spoiling the agreement with experiment