Enhanced electroweak penguin amplitude in B-->VV decays

We discuss a novel electromagnetic penguin contribution to the transverse helicity amplitudes in B decays to two vector mesons, which is enhanced by two powers of mB/Lambda relative to the standard penguin amplitudes. This leads to unique polarization signatures in penguin-dominated decay modes such as B-->rho K* similar to polarization effects in the radiative decay B-->K*gamma, and offers new opportunities to probe the magnitude and chirality of flavour-changing neutral current couplings to photons.Comment: 4 pages, 1 figur

Non-perturbative effects in semi-leptonic B_c decays

We discuss the impact of the soft degrees of freedom inside the B_c meson on its rate in the semi-leptonic decay B_c -> X l nu_l where X denotes light hadrons below the D^0 threshold. In particular we identify contributions involving soft hadrons which are non-vanishing in the limit of massless leptons. These contributions become relevant for a measurement of the purely leptonic B_c decay rate, which due to helicity suppression involves a factor m_l^2 and thus is much smaller than the contributions involving soft hadrons.Comment: LaTeX, 22 pages, 1 figur

Two body non-leptonic Λb\Lambda_b decays in quark model with factorization ansatz

The two body non-leptonic $\Lambda_b$ decays are analyzed in factorization approximation, using quark model, $\xi = 1 / N_c$ as a free parameter. It is shown that the experimental branching ratio for $\Lambda_b \longrightarrow \Lambda {J/\psi}$ restricts $\xi$ and this ratio can be understood for a value of $\xi$ which lies in the range $0 \leq \xi \leq 0.5$ suggested by two body B meson decays. The branching ratios for $\Lambda_b \longrightarrow \Lambda_{c} D^*_s(D_s)$ are predicted to be larger than the previous estimates. Finally it is pointed that CKM-Wolfenstein parameter $\rho^2 + \eta^2$, where $\eta$ is CP phase, can be determined from the ratio of widths of $\Lambda_b \longrightarrow \Lambda \bar{D}$ and $\Lambda_b \longrightarrow \Lambda {J/\psi}$ or that of $\Lambda_b \longrightarrow p D_s$ and $\Lambda_b \longrightarrow \Lambda_c D_s$ independent of the parameter $\xi$.Comment: 18 pages, latex, 1 figure available on request, please send any questions or comments to [email protected]

Sequential Flavour Symmetry Breaking

The gauge sector of the Standard Model (SM) exhibits a flavour symmetry which allows for independent unitary transformations of the fermion multiplets. In the SM the flavour symmetry is broken by the Yukawa couplings to the Higgs boson, and the resulting fermion masses and mixing angles show a pronounced hierarchy. In this work we connect the observed hierarchy to a sequence of intermediate effective theories, where the flavour symmetries are broken in a step-wise fashion by vacuum expectation values of suitably constructed spurion fields. We identify the possible scenarios in the quark sector and discuss some implications of this approach.Comment: 22 pages latex, no figure

B-Meson Distribution Amplitudes of Geometric Twist vs. Dynamical Twist

Two- and three-particle distribution amplitudes of heavy pseudoscalar mesons of well-defined geometric twist are introduced. They are obtained from appropriately parametrized vacuum-to-meson matrix elements by applying those twist projectors which determine the enclosed light-cone operators of definite geometric twist and, in addition, observing the heavy quark constraint. Comparing these distribution amplitudes with the conventional ones of dynamical twist we derive relations between them, partially being of Wandzura-Wilczek type; also sum rules of Burkhardt-Cottingham type are derived.The derivation is performed for the (double) Mellin moments and then re-summed to the non-local distribution amplitudes. Furthermore, a parametrization of vacuum-to-meson matrix elements for non-local operators off the light-cone in terms of distribution amplitudes accompanying independent kinematical structures is derived.Comment: 18 pages, Latex 2e, no figure

Wopper, Version 1.1: A Monte Carlo Event Generator for Four Fermion Production at LEP-II and Beyond

We report on the status of the Monte Carlo event generator WOPPER. Version 1.1 of WOPPER describes four fermion production at LEP-II and beyond with leading logarithmic radiative corrections in the double W pole approximation. These approximations are appropriate for almost all practical purposes, but the inclusion of these finite width effects and radiative corrections is nevertheless indispensable for LEP-II physics.Comment: 6 pages LaTeX (Elsevier proceedings style) with 7 PostScript figures, (Contribution to the Teupitz Workshop 1994), IKDA 94/

Interferon γ and lymphotoxin or tumor necrosis factor act synergistically to induce macrophage killing of tumor cells and schistosomula of schistosoma mansoni

Macrophages play a crucial role in the defense against tumors and parasites. Activation of tumoricidal and microbicidal effector mechanisms requires stimulation of macrophages with macrophage-activating factors (MAF). One such MAF is interferon γ (IFN-γ). In some assays, substantial activity of IFN-γ on murine macrophages, however, is only observed in synergy with lipopolysaccharide (LPS) or other cytokines (1). In addition, certain cytokines have been shown to induce monocyte or macrophage activation in the absence of IFN-γ (2-5). We previously described lymphokines in the supernatant of a murine T cell clone that synergized with IFN-γ in the induction of tumoricidal and schistosomulicidal murine macrophages (1). We called this lymphokine(s) macrophage cytotoxicityinducing factor 2 (MCIF2)(1). A candidate for MCIF2 was lymphotoxin (LT), because the T cell clone supernatant contained high amounts of LT. LT is functionally homologous and structurally related to the macrophage product tumor necrosis factor (TNF). Therefore, we tested whether recombinant (r) LT or rTNF can function as MAF. We report here that rLT or rTNF synergize with rIFN-γ in the induction of tumoricidal and schistosomulicidal murine macrophages

Higher Order Power Corrections in Inclusive B Decays

We discuss order 1/m_b^4 and 1/m_b^5 corrections in inclusive semileptonic decay of a $B$ meson. We identify relevant hadronic matrix elements of dimension seven and eight and estimate them using the ground-state saturation approximation. Within this approach the effects on the integrated rate and on kinematic moments are estimated. The overall relative shift in V_{cb} turns out about +0.4% as applied to the existing fits. Similar estimates are presented for B -> X_s+\gamma decays.Comment: 30 pages, 16 figure