arXiv subjects
Publications and source records attributed to B. Blok.
QCD-based analysis of nonfactorizable parts of weak nonleptonic amplitudes is reported. Nonperturbative effects due to soft gluon exchange play a key role leading to the emergence of a dynamical rule of discarding $1/N_c$ corrections.
We calculate the leading preasymptotic correction to the inclusive width $b\rightarrow \bar c c s$ (two massive quarks in the final state) due to the operator $\vec σ\vec H$. It is found that this correction tends to cancel the $1/N_c$ part of the inclusive width calculated using naive factorization. The absolute value of the effect is of order 0.25. We also discuss how quark-hadron duality is realized in the inclusive decays.
We continue to investigate the effects of the (dominant) subleading operator of the $\vecσ\vec H$ type in the $1/N_c$ parts of the weak nonleptonic amplitudes. If the previous work concentrated on exclusive decays now we analyse inclusive widths in a certain kinematic limit. Deviations from the parton model predictions are found due to soft-gluon color exchange. In the interference (i.e. $1/N_c$) terms they are stronger than in the non-interference terms. The sign is negative so that the $1/N_c$ parts tend to cancel. The absolute value of the effect is of order 1 in D-mesons and of order 0.50 in B mesons.
We discuss the Isgur-Wise function $ξ(y)$ in the small velocity (SV) limit within the QCD sum rule method. The behavior of $ξ(y)$ in the SV limit is sensitive to the particular form of the duality relations used to decontaminate the sum rule predictions from the continuum contribution. Peculiarities of the duality relations in the problem at hand are revealed. It is shown that the proper requirements of duality and angular isotropy for S wave states lead to an unambiguous form of the sum rules for the Isgur-Wise function. We illustrate the constraints due to these requirements using a toy model of the harmonic oscillator. The slope parameter and the shape of $ξ(y)$ are determined.
We estimate nonfactorizable 1/$N_c$ contributions in the $K\rightarrow 2π$ amplitudes using the approach proposed in our previous work. It is demonstrated that for the conventional (nonpenguin) operators these contributions are close in magnitude to factorizable $1/N_c$ parts and have the opposite sign. Thus, an approximate rule of discarding $1/N_c$ corrections in $K\rightarrow 2π$ decays is theoretically confirmed. As a result we find an extra suppression of the matrix element of $O_4$ ($ΔI=3/2$) and an extra enhancement of the matrix element of $O_1$ ($ΔI=1/2$). The parameter $B$ describing $K^0-\bar K^0$ mixing is also discussed.
We discuss nonfactorizable $1/N_c$ contributions in the amplitudes of non-leptonic exclusive decays of the type $B\rightarrow Dπ$ ($N_c$ is the number of colors). In a certain kinematical limit rather reliable estimates are possible. It is demonstrated that the nonfactorizable parts are of the same order as the factorizable $1/N_c$ parts of the ampiltudes, and have the opposite sign. Thus, an approximate rule of discarding $1/N_c$ corrections in the nonleptonic exclusive decays emerges dynamically. It is shown that this rule is not exact and the degree of compensation is different in different channels. Our predictions make use of the fact that a key matrix element that measures deviations from factorization can be determined using the heavy quark effective theory.