Dmitri Melikhov

Form-factors of meson decays in the relativistic constituent quark model

A formalism for the relativistic description of hadron decays within the constituent quark model is presented. First, hadron amplitudes of the light-cone constituent quark model, in particular, the weak transition form factors at spacelike momentum transfers, are represented in the form of dispersion integrals over the hadron mass. Second, the form factors at timelike momentum transfers are obtained by performing the analytic continuation from the region {ital q}{sup 2}{le}0. As a result, the transition form factors both in the scattering and the decay regions are expressed through light-cone wave functions of the initial and final hadrons. The technique is applied to the description of the semileptonic decays of pseudoscalar mesons and direct calculation of the transition form factors at {ital q}{sup 2}{approx_gt}0. Meson properties in the heavy quark limit are investigated. {copyright} {ital 1996 The American Physical Society.}

Rare exclusive semileptonic b ---> s transitions in the standard model

We study long-distance effects in rare exclusive semileptonic decays B -> (K, K*) (l+ l-, nu bar{nu}) and analyze dilepton spectra and asymmetries within the framework of the Standard Model. The form factors, describing the meson transition amplitudes of the effective Hamiltonian are calculated within the lattice-constrained dispersion quark model: the form factors are given by dispersion representations through the wave functions of the initial and final mesons, and these wave functions are chosen such that the B -> K* transition form factors agree with the lattice results at large q**2. We calculate branching ratios of semileptonic B -> K, K* transition modes and study the sensitivity of observables to the long-distance contributions. The shape of the forward-backward asymmetry and the longitudinal lepton polarization asymmetry are found to be independent of the long-distance effects and mainly determined by the values of the Wilson coefficients in the Standard Model.

Decay constants of heavy pseudoscalar mesons from QCD sum rules

We revisit the sum-rule extraction of the decay constants of the D, Ds, B and Bs mesons from the two-point correlator of heavy?light pseudoscalar currents. We use the operator product expansion of this correlator expressed in terms of the heavy-quark mass for which the perturbative expansion exhibits a reasonable convergence. Our main emphasis is laid on the control over the uncertainties in the decay constants, related both to the input quantum chromodynamics (QCD) parameters and to the limited intrinsic accuracy of the method of QCD sum rules. This becomes possible due to the application of our procedure of extracting hadron observables that involves as novel feature dual thresholds depending on the Borel parameter. For charmed mesons, we find the decay constants and . For beauty mesons, the decay constants turn out to be extremely sensitive to the precise value of . By requiring our sum-rule estimate to match the average of the lattice results for fB, a very accurate value is extracted, leading to fB = (193.4 ? 12.3(OPE) ? 4.3(syst))?MeV and .

Systematic uncertainties of hadron parameters obtained with QCD sum rules

We study the uncertainties of the determination of the ground-state parameters from Shifman-Vainshtein-Zakharov (SVZ) sum rules, making use of the harmonic-oscillator potential model as an example. In this case, one knows the exact solution for the polarization operator

Decay constants of the charmed vector mesons D⁎ and Ds⁎ from QCD sum rules

\ensuremath{\Pi}(\ensuremath{\mu})

Quark structure of the pion and pion form-factor

, which allows one to obtain both the operator product expansion (OPE) to any order and the spectrum of states. We start with the OPE for

OPE, charm-quark mass, and decay constants of D and Ds mesons from QCD sum rules.

\ensuremath{\Pi}(\ensuremath{\mu})

Accuracy of bound-state form-factors extracted from dispersive sum rules

and analyze the extraction of the square of the ground-state wave function,

Extraction of ground-state decay constant from dispersive sum rules: QCD vs potential models

R\ensuremath{\propto}|{\ensuremath{\Psi}}_{0}(\stackrel{\ensuremath{\rightarrow}}{r}=0){|}^{2}

Can one control systematic errors of QCD sum rule predictions for bound states

, from an SVZ sum rule, setting the mass of the ground state