Semileptonic decays of heavy mesons

The semileptonic and leptonic decays of heavy mesons are studied as a phenomenological application and exploration of a heavy-quark limit of Dyson-Schwinger equations. The single form factor, $\xi(w)$, which characterises the semileptonic decay in this limit, is calculated and compares well with recent experimental extractions. We obtain a lower bound of 1/3 on the slope-parameter $\rho^2 \equiv -\xi^\prime(1)$, which, in calculations with realistic input, is exceeded by a great deal: agreement with experimental data requiring $\rho^2 \sim 1.2 - 1.6$. The flavour and momentum dependence of the light-quark propagators has observable consequences.Comment: 11 pages, LaTeX, epsfig.sty, elsart.st

Leptonic and semileptonic decays of heavy mesons

A heavy-quark limit of the Dyson-Schwinger equations is introduced and used in an exploratory study of leptonic and semileptonic decays of heavy mesons. The application of this framework to heavy-to-light semileptonic decays, which require a good knowledge of light-quark propagation characteristics and light-meson bound state amplitudes, is illustrated.Comment: 4 pages, 2 figures, Contribution to the IVth International Workshop on Progress in Heavy Quark Physics, 20-22 Sept. 1997, Rostoc

Electroproduction of Charmonia off Protons and Nuclei

Elastic virtual photoproduction of charmonia on nucleons is calculated in a parameter free way with the light-cone dipole formalism and the same input: factorization in impact parameters, light-cone wave functions for the photons and the charmonia, and the universal phenomenological dipole cross section which is fitted to other data. The charmonium wave functions are calculated with four known realistic potentials, and two models for the dipole cross section are tested. Very good agreement with data for the cross section of charmonium electroproduction is found in a wide range of $s$ and $Q^2$. Using the ingredients from those calculations we calculate also exclusive electroproduction of charmonia off nuclei. Here new effects become important, (i) color filtering of the $c\bar c$ pair on its trajectory through nuclear matter, (ii) dependence on the finite lifetime of the $c\bar c$ fluctuation (coherence length) and (iii) gluon shadowing in a nucleus compared to the one in a nucleon. Total coherent and incoherent cross sections for C, Cu and Pb as functions of $s$ are presented. The results can be tested with future electron-nucleus colliders or in the peripheral collisions of relativistic heavy ions.Comment: Talk at 2-nd International Workshop on Hadron Physics, 25-29 September 2002, Coimbra, Portugal. To appear in the Workshop Proceedings (will be published by the American Institute of Physics

Radiative Tau Decays with One Pseudoscalar Meson

We have calculated the decay $\tau \rightarrow \nu \pi(K) \gamma$. We present the photon energy spectrum, the meson-photon invariant mass spectrum and the integrated rate as a function of a photon energy cut or an invariant mass cut. Both the internal bremsstrahlung and the structure dependent radiation have been taken into account. To this aim we have parametrized the form factors $F_V$ and $F_A$, which determine the structure dependent radiation. Observables especially suited for the measurement of the structure dependent form factors are found and implications on the width of the $a_1$ discussed.Comment: p.20, TTP93-1, LaTe

Self-consistent Approach to Off-Shell Transport

The properties of two forms of the gradient expanded Kadanoff--Baym equations, i.e. the Kadanoff--Baym and Botermans-Malfliet forms, suitable to describe the transport dynamics of particles and resonances with broad spectral widths, are discussed in context of conservation laws, the definition of a kinetic entropy and the possibility of numerical realization. Recent results on exact conservations of charge and energy-momentum within Kadanoff-Baym form of quantum kinetics based on local coupling schemes are extended to two cases relevant in many applications. These concern the interaction via a finite range potential, and, relevant in nuclear and hadron physics, e.g. for the pion--nucleon interaction, the case of derivative coupling.Comment: 35 pages, submitted to issue of Phys. Atom. Nucl. dedicated to S.T. Belyaev on the occasion of his 80th birthday. Few references are adde