372 research outputs found

    Role of gauge invariance in B -> V gamma radiative weak decays

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    The role of gauge invariance in calculating B -> V gamma radiative weak decays is clarified. It is shown that the gauge invariance severely restricts the contributions mediated by the usual weak non-leptonic Hamiltonian dominated by u and c quaks with one photon attachment. Such contributions are found to be almost negligible.Comment: 5 pages, Revtex, no figure

    Hadronic Form Factors: Combining QCD Calculations with Analyticity

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    I discuss recent applications of QCD light-cone sum rules to various form factors of pseudoscalar mesons. In this approach both soft and hard contributions to the form factors are taken into account. Combining QCD calculation with the analyticity of the form factors, one enlarges the region of accessible momentum transfers.Comment: 12 pages, 3 figures, Talk at the Workshop "Shifmania, Crossing the boundaries: Gauge dynamics at strong coupling", May 14-17,2009, Minneapolis, USA; table entry and reference update

    BπνlB \to \pi \ell \nu_l Width and Vub|V_{ub}| from QCD Light-Cone Sum Rules

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    We employ the BπB\to\pi form factors obtained from QCD light-cone sum rules and calculate the BπνlB\to \pi \ell \nu_l width (=e,μ\ell=e,\mu) in units of 1/Vub21/|V_{ub}|^2, integrated over the region of accessible momentum transfers, 0q212.0 GeV20\leq q^2\leq 12.0 ~GeV^2. Using the most recent BABAR-collaboration measurements we extract Vub=(3.500.33+0.38th.±0.11exp.)×103|V_{ub}|=(3.50^{+0.38}_{-0.33}\big|_{th.}\pm 0.11 \big|_{exp.})\times 10^{-3}. The sum rule results for the form factors, taken as an input for a zz-series parameterization, yield the q2q^2-shape in the whole semileptonic region of BπνB\to \pi\ell\nu_\ell. We also present the charged lepton energy spectrum in this decay. Furthermore, the current situation with BτντB\to \tau\nu_\tau is discussed from the QCD point of view. We suggest to use the ratio of the BπτντB\to \pi \tau\nu_\tau and Bπνl (=μ,e)B\to \pi\ell \nu_l ~(\ell =\mu,e) widths as an additional test of Standard Model. The sensitivity of this observable to new physics is illustrated by including a charged Higgs-boson contribution in the semileptonic decay amplitude.Comment: 22 pages, 8 figures; comments added in section 4, version to be published in Phys. Rev.

    Direct CP asymmetry in Dππ+D\to \pi^-\pi^+ and DKK+D\to K^-K^+ in QCD-based approach

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    We present the first QCD-based calculation of hadronic matrix elements with penguin topology determining direct CP-violating asymmetries in D0ππ+D^0\to \pi^-\pi^+ and D0KK+D^0\to K^- K^+ nonleptonic decays. The method is based on the QCD light-cone sum rules and does not rely on any model-inspired amplitude decomposition, instead leaning heavily on quark-hadron duality. We provide a Standard Model estimate of the direct CP-violating asymmetries in both pion and kaon modes and their difference and comment on further improvements of the presented computation.Comment: 19 pages, 1 figure; replaced to match published version (minor changes to text and a figure, added new references

    Perturbative QCD Correction to the Light-Cone Sum Rule for the BBπB^*B\pi and DDπD^*D\pi Couplings

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    The BBπB^*B\pi and DDπD^*D\pi couplings have previously been derived from a QCD light-cone sum rule in leading order. Here, we describe the calculation of the O(αs)O(\alpha_s) correction to the twist 2 term of this sum rule. The result is used for a first next-to-leading order analysis. We obtain gBBπ=22±7g_{B^*B\pi}= 22\pm 7 and gDDπ=10.5±3g_{D^*D\pi}=10.5\pm 3, where the error indicates the remaining theoretical uncertainty.Comment: 11 pages, 1 figure, Latex, epsfi