Renormalization of B-meson distribution amplitudes

We summarize a recent calculation of the evolution kernels of the two-particle B-meson distribution amplitudes $\phi_+$ and $\phi_-$ taking into account three-particle contributions. In addition to a few phenomenological comments, we give as a new result the evolution kernel of the combination of three-particle distribution amplitudes $\Psi_A-\Psi_V$ and confirm constraints on $\phi_+$ and $\phi_-$ derived from the light-quark equation of motion.Comment: 7 pages, 2 figures. Contribution to the proceedings of the Int. Workshop on Effective Field Theories: from the pion to the upsilon. Feb. 2009. Valencia, Spai

Evolution equation for the higher-twist B-meson distribution amplitude

We find that the evolution equation for the three-particle quark-gluon B-meson light-cone distribution amplitude (DA) of subleading twist is completely integrable in the large $N_c$ limit and can be solved exactly. The lowest anomalous dimension is separated from the remaining, continuous, spectrum by a finite gap. The corresponding eigenfunction coincides with the contribution of quark-gluon states to the two-particle DA $\phi_-(\omega)$ so that the evolution equation for the latter is the same as for the leading-twist DA $\phi_+(\omega)$ up to a constant shift in the anomalous dimension. Thus, ``genuine'' three-particle states that belong to the continuous spectrum effectively decouple from $\phi_-(\omega)$ to the leading-order accuracy. In turn, the scale dependence of the full three-particle DA turns out to be nontrivial so that the contribution with the lowest anomalous dimension does not become leading at any scale. The results are illustrated on a simple model that can be used in studies of $1/m_b$ corrections to heavy-meson decays in the framework of QCD factorization or light-cone sum rules.Comment: Extended version, includes new results on the large momentum limit and a detailed study of the evolution effects in a simple mode

Axial form factor of the nucleon at large momentum transfers

Motivated by the emerging possibilities to study threshold pion electroproduction at large momentum transfers at Jefferson Laboratory following the 12 GeV upgrade, we provide a short theory summary and an estimate of the nucleon axial form factor for large virtualities in the $Q^2 = 1-10~\text{GeV}^2$ range using next-to-leading order light-cone sum rules.Comment: A comparison to the new neutrino data analysis and several references added. Final version to appear in Phys.Rev.

Nucleon Form Factors and Distribution Amplitudes in QCD

We derive light-cone sum rules for the electromagnetic nucleon form factors including the next-to-leading-order corrections for the contribution of twist-three and twist-four operators and a consistent treatment of the nucleon mass corrections. The essence of this approach is that soft Feynman contributions are calculated in terms of small transverse distance quantities using dispersion relations and duality. The form factors are thus expressed in terms of nucleon wave functions at small transverse separations, called distribution amplitudes, without any additional parameters. The distribution amplitudes, therefore, can be extracted from the comparison with the experimental data on form factors and compared to the results of lattice QCD simulations. A selfconsistent picture emerges, with the three valence quarks carrying 40%:30%:30% of the proton momentum.Comment: 27 pages, 7 figures uses revte

BELLE Data on the π0γ∗γ\pi^0 \gamma* \gamma Form Factor: A Game Changer?

We extend our analysis of the $\pi^0\gamma^*\gamma$ form factor by including a comparison with the new BELLE data. The necessity of new precision measurements in a broad interval of momentum transfers is emphasized.Comment: 4 pages, 3 figures. Addendum to Phys. Rev. D 83, 054020 (2011

Semileptonic charm decays D \to \pi l \nu_{\l} and D→KlνlD \to K l \nu_l from QCD Light-Cone Sum Rules

We present a new calculation of the $D\to\pi$ and $D \to K$ form factors from QCD light-cone sum rules. The $\overline{MS}$ scheme for the $c$-quark mass is used and the input parameters are updated. The results are $f^+_{D\pi}(0)= 0.67^{+0.10}_{-0.07}$, $f^+_{DK}(0)=0.75^{+0.11}_{-0.08}$ and $f^+_{D\pi}(0)/f^+_{DK}(0)=0.88 \pm 0.05$. Combining the calculated form factors with the latest CLEO data, we obtain $|V_{cd}|=0.225\pm 0.005 \pm 0.003 ^{+0.016}_{-0.012}$ and $|V_{cd}|/|V_{cs}|= 0.236\pm 0.006\pm 0.003\pm 0.013$ where the first and second errors are of experimental origin and the third error is due to the estimated uncertainties of our calculation. We also evaluate the form factors $f^-_{D\pi}$ and $f^-_{DK}$ and predict the slope parameters at $q^2=0$. Furthermore, calculating the form factors from the sum rules at $q^2<0$, we fit them to various parameterizations. After analytic continuation, the shape of the $D\to \pi,K$ form factors in the whole semileptonic region is reproduced, in a good agreement with experiment.Comment: 34 pages, 5 figure

B→πℓνlB \to \pi \ell \nu_l Width and ∣Vub∣|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.