0000000000501175
AUTHOR
Blaženka Melić
BLM scale for the pion transition form factor
The NLO Brodsky-Lepage-Mackenzie (BLM) scale for the pion transition form factor has been determined. To achieve that, a consistent calculation up to nf-proportional NNLO contributions to both the hard-scattering amplitude and the perturbatively calculable part of the pion distribution amplitude has been performed. By combining and matching the results obtained for these two amplitudes, a proper cancellation of collinear singularities has been established and the gamma5 ambiguity problem (related to the use of the dimensional regularization method) has been resolved by using the naive-gamma5 as well as the 't Hooft-Veltman (HV) schemes. It has been demonstrated that the prediction for the p…
Brodsky-Lepage-Mackenzie scale for the pion transition form factor
The next-to-leading order (NLO) Brodsky-Lepage-Mackenzie (BLM) scale for the pion transition form factor is determined. To achieve that, a consistent calculation up to ${n}_{f}$-proportional next-to-next-to-leading order contributions to both the hard-scattering amplitude and the perturbatively calculable part of the pion distribution amplitude is performed. By combining and matching the results obtained for these two amplitudes, a proper cancellation of collinear singularities is established and the ${\ensuremath{\gamma}}_{5}$ ambiguity problem (related to the use of the dimensional regularization method) is resolved by using the naive-${\ensuremath{\gamma}}_{5}$ as well as the 't Hooft--V…
Next-to-next-to-leading order prediction for the photon-to-pion transition form factor
We evaluate the next-to-next-to-leading order corrections to the hard-scattering amplitude of the photon-to-pion transition form factor. Our approach is based on the predictive power of the conformal operator product expansion, which is valid for a vanishing $\beta$-function in the so-called conformal scheme. The Wilson--coefficients appearing in the non-forward kinematics are then entirely determined from those of the polarized deep-inelastic scattering known to next-to-next-to-leading accuracy. We propose different schemes to include explicitly also the conformal symmetry breaking term proportional to the $\beta$-function, and discuss numerical predictions calculated in different kinemati…
Exclusive/inclusive ratio of semileptonicΛbdecays
We present theoretical evidence that the exclusive/inclusive ratio of semileptonic ${\ensuremath{\Lambda}}_{b}$ decays exceeds that of semileptonic B decays where the experimental exclusive/inclusive ratio amounts to about 66%. We start from the observation that the spectator quark model provides a lower bound on the leading order Isgur-Wise function of the ${\ensuremath{\Lambda}}_{b}\ensuremath{\rightarrow}{\ensuremath{\Lambda}}_{c}$ transition in terms of the corresponding $\stackrel{\ensuremath{\rightarrow}}{B}{D,D}^{*}$ mesonic Isgur-Wise function. Using experimental data for the $\stackrel{\ensuremath{\rightarrow}}{B}{D,D}^{*}$ mesonic Isgur-Wise functions this bound is established. Ap…
Nonfactorizable corrections toB→J/ψK
We apply the method of QCD light-cone sum rules to calculate nonfactorizable contributions to the $\stackrel{\ensuremath{\rightarrow}}{B}J/\ensuremath{\psi}K$ decay and estimate soft nonfactorizable corrections to the ${a}_{2}$ parameter. The corrections appear to be positive, favoring the positive sign of ${a}_{2},$ in agreement with recent theoretical considerations and experimental data. Our result also confirms expectations that in the color-suppressed decay nonfactorizable corrections are sizable.