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We critically reexamine the formalism for treating the leading-twist contributions from the two-gluon Fock components occurring in hard processes that involve eta and eta' mesons and establish a consistent set of conventions for the definition of the gluon distribution amplitudes, the anomalous dimensions as well as the projector of a two-gluon state onto an eta or eta' state. We calculate the eta, eta'--photon transition form factor to order alpha_s and show the cancellation of the collinear and UV singularities explicitly. An estimate of the lowest Gegenbauer coefficients of the gluon and quark distribution amplitudes is obtained from a fit to the eta, eta'--photon transition form factor data. In order to elucidate the role of the two-gluon Fock component further, we analyze electroproduction of eta, eta' mesons and the g*g* eta (eta') vertex., 20 pages(revtex4 two-column format), 14 figures; a typo corrected; version published in Phys. Rev. D

We calculate the transition form factors that occur in heavy $\Lambda$-type baryon semileptonic decays as e.g. in $\Lambda_{b} \to \Lambda_{c}^{+} + l^{-} + \bar{\nu}_{l} $. We use Bauer-Stech-Wirbel type infinite momentum frame wave functions for the heavy $\Lambda$-type baryons which we assume to consist of a heavy quark and a light spin-isospin zero diquark system. The form factors at $ q^{2} = 0 $ are calculated from the overlap integrals of the initial and final $\Lambda$-type baryon states. To leading order in the heavy mass scale the structure of the form factors agrees with the HQET predictions including the normalization at zero recoil. The leading order $\omega$-dependence of the form factors is extracted by scaling arguments. By comparing the model form factors with the HQET predictions at ${\cal O}(1/m_{Q})$ we obtain a consistent set of model form factors up to ${\cal O}(1/m_{Q})$. With our preferred choice of parameter values we find that the contribution of the non-leading form factor is practically negligible. We use our form factor predictions to compute rates, spectra and various asymmetry parameters for the semi-leptonic decay $\Lambda_{b} \to \Lambda_{c}^{+} + l^{-} + \bar{\nu}_{l} $., Comment: 24 pages, LaTeX, 6 figures are included in PostScript format. Final version of paper to appear in Phys.Rev.D

22 pp. (1997). doi:10.3204/PUBDB-2017-09921, We calculate the transition form factors that occur in heavy Λ-type baryon semileptonic decays such as, e.g., in Λb→Λ+c+l−+ν¯l. We use Bauer-Stech-Wirbel-type infinite momentum frame wave functions for the heavy Λ-type baryons which we assume to consist of a heavy quark and a light spin-isospin zero diquark system. The form factors at q2=0 are calculated from the overlap integrals of the initial and final Λ-type baryon states. To leading order in the heavy mass scale the structure of the form factors agrees with the HQET predictions including the normalization at zero recoil. The leading order ω dependence of the form factors is extracted by scaling arguments. By comparing the model form factors with the HQET predictions at O(1/mQ) we obtain a consistent set of model form factors up to O(1/mQ). With our preferred choice of parameter values we find that the contribution of the nonleading form factor is practically negligible. We use our form factor predictions to compute rates, spectra, and various asymmetry parameters for the semileptonic decay Λb→Λ+c+l−+ν¯l.

The reactions gamma p -> K+ Lambda and gamma p -> K* Lambda are analyzed within perturbative QCD, allowing for diquarks as quasi-elementary constituents of baryons. The diquark-model parameters and the quark-diquark distribution amplitudes of proton and Lambda are taken from previous investigations of electromagnetic baryon form factors and Compton-scattering off protons. Unpolarized differential cross sections and polarization observables are computed for different choices of the K and K* distribution amplitudes. The asymptotic form of the K distribution amplitude (proportional to x1 x2) is found to provide a satisfactory description of the K photoproduction data., 32 pages, 7 figures available as tared, compressed and uuencoded PS-files