372 research outputs found

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

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

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

### $B \to \pi \ell \nu_l$ Width and $|V_{ub}|$ from QCD Light-Cone Sum Rules

We employ the $B\to\pi$ form factors obtained from QCD light-cone sum rules
and calculate the $B\to \pi \ell \nu_l$ width ($\ell=e,\mu$) in units of
$1/|V_{ub}|^2$, integrated over the region of accessible momentum transfers,
$0\leq q^2\leq 12.0 ~GeV^2$. Using the most recent BABAR-collaboration
measurements we extract $|V_{ub}|=(3.50^{+0.38}_{-0.33}\big|_{th.}\pm 0.11
\big|_{exp.})\times 10^{-3}$. The sum rule results for the form factors, taken
as an input for a $z$-series parameterization, yield the $q^2$-shape in the
whole semileptonic region of $B\to \pi\ell\nu_\ell$. We also present the
charged lepton energy spectrum in this decay. Furthermore, the current
situation with $B\to \tau\nu_\tau$ is discussed from the QCD point of view. We
suggest to use the ratio of the $B\to \pi \tau\nu_\tau$ and $B\to \pi\ell \nu_l
~(\ell =\mu,e)$ 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 $D\to \pi^-\pi^+$ and $D\to K^-K^+$ in QCD-based approach

We present the first QCD-based calculation of hadronic matrix elements with
penguin topology determining direct CP-violating asymmetries in $D^0\to
\pi^-\pi^+$ and $D^0\to K^- K^+$ 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 $B^*B\pi$ and $D^*D\pi$ Couplings

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

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