Analysis of the strong coupling form factors of Σ_bNB and Σ_cND in QCD sum rules

In this article, we study the strong interaction of the vertices Σ_bNB and Σ_cND using the three-point QCD sum rules under two different Dirac structures. Considering the contributions of the vacuum condensates up to dimension 5 in the operation product expansion, the form factors of these vertices are calculated. Then, we fit the form factors into analytical functions and extrapolate them into time-like regions, which gives the coupling constants. Our analysis indicates that the coupling constants for these two vertices are G_(Σ_bNB)= 0.43±0.01 GeV~(-1) and G_(Σ_cND)=3.76±0.05 GeV~(-1).     

Λb → Λc form factors from QCD light-cone sum rules

In this study, we calculate the transition form factors of \begin{document}$ \Lambda_b $\end{document} decaying into \begin{document}$ \Lambda_c $\end{document} within the framework of light-cone sum rules with the distribution amplitudes (DAs) of the \begin{document}$ \Lambda_b $\end{document}-baryon. In the hadronic representation of the correlation function, we isolate both the \begin{document}$ \Lambda_c $\end{document} and \begin{document}$ \Lambda_c^* $\end{document} states so that the \begin{document}$ \Lambda_b \rightarrow \Lambda_c $\end{document}form factors can be obtained without ambiguity. We investigate the P-type and A-type currents to interpolate light baryons for comparison because the interpolation current for the baryon state is not unique. We also employ three parametrization models for the DAs of \begin{document}$ \Lambda_b $\end{document} in the numerical calculation. We present the numerical predictions for the \begin{document}$ \Lambda_b \rightarrow \Lambda_c $\end{document} form factors and branching fractions, averaged forward-backward asymmetry, averaged final hadron polarization, and averaged lepton polarization of the \begin{document}$ \Lambda_b \to \Lambda_c \ell\mu $\end{document} decays, as well as the ratio of the branching ratios \begin{document}$ R_{\Lambda_c} $\end{document}. The predicted \begin{document}$ R_{\Lambda_c} $\end{document} is consistent with LHCb data.     

B → A transitions in the light-cone QCD sum rules with the chiral current

In this article, we calculate the form-factors of the transitions B → a₁(1260), b₁(1235) in the leading-order approximation using the light-cone QCD sum rules. In calculations, we choose the chiral current to interpolate the B-meson, which has the outstanding advantage that the twist-3 light-cone distribution amplitudes of the axial-vector mesons makes no contributions, and the resulting sum rules for the form-factors suffer from far fewer uncertainties. Then we study the semi-leptonic decays B → a₁(1260) lv_l, b₁(1235) lv_l (l=e,μ,τ), and make predictions for the differential decay widths and decay widths, which can be compared with the experimental data in the coming future.     

B → A transitions in the light-cone QCD sum rules with the chiral current

In this article, we calculate the form-factors of the transitions B → a₁(1260), b₁(1235) in the leading-order approximation using the light-cone QCD sum rules. In calculations, we choose the chiral current to interpolate the B-meson, which has the outstanding advantage that the twist-3 light-cone distribution amplitudes of the axial-vector mesons makes no contributions, and the resulting sum rules for the form-factors suffer from far fewer uncertainties. Then we study the semi-leptonic decays B → a₁(1260) lv_l, b₁(1235) lv_l (l=e,μ,τ), and make predictions for the differential decay widths and decay widths, which can be compared with the experimental data in the coming future.     

QCD sum rule calculation ofK ℓ3 form factors

We present a combined finite energy sum rule (FESR) and analytic continuation by duality (ACD) calculation of the (neutral)K ₃ decay. We confirm the Callan-Treiman relation and investigaté the validity of a linear fit for the form factors. Furthermore, we obtain =–0.1...–0.3, consistent with the mean experimental value =–0.1±0.09.Supported by Bundesministerium für Forschung und Technologie under contract number 06 Mz 758     

Dispersive methods and QCD sum rules for γ γ collisions

It has been shown, in the case of meson photoproduction, that the power-law falloff of these reactions can be described by lowest-order (real) sum rules, at moderate momentum transfer. The phases of these processes, in this regime, are usually thought to be non-perturbative. In a sum rule framework, however, they can possibly be described by radiative corrections to the hadronic spectral densities of the corresponding helicities, which become complex functions to order α_s, and the effects of interference can be strongly enhanced by the presence of the vacuum condensates in the dispersion relation. It is shown that the imaginary parts of these complex corrections have a factorized form and can be evaluated in a systematic fashion, while their real parts, at the same perturbative order, are down by at least two powers of momentum transfer. The analysis is done at two-loop level, combining dimensional regularization and light-cone methods. The calculations are performed for all the independent set of scalar diagrams generated by the OPE. The analytical bounds are identified and discussed.     

The coupling constants g Vσγ in QCD sum rules

We review and update previous calculations of the coupling constants g _Vσγ and also determine new variables including the magnetic susceptibility of the quark condensate in QCD sum rules. Our estimates are consistent with the values obtained in the literature.     

The cross section of the process e ++e −→J/ψ+η c within the QCD light-cone sum rules

We calculate the cross section of the exclusive process e ⁺+e ^?→J/ψ+η _c at the leading order approximation within the QCD light-cone sum rules approach. It is found that the form factor F _VP(V=J/ψ,P=η _c ) depends mainly on the behavior of the twist-2 distribution amplitude of the η _c meson at the scale of this process. Thus in order to obtain a reliable estimation of the cross section, it is important to have a realistic distribution amplitude of the η _c meson and to deal with the evolution of the distribution amplitude to the effective energy scale of the process. Our results show that one can obtain a compatible prediction with the Belle and BaBar experimental data.     

D~*Dρ and B~*Bρ strong couplings in light-cone sum rules

We present an improved calculation of the strong coupling constants g_(D~*Dp) and g_(B~*Bp) in light-cone sum rules, including one-loop QCD corrections of leading power with meson distribution amplitudes. We further compute subleading-power corrections from two-particle and three-particle higher-twist contributions at leading order up to twist-4 accuracy. The next-to-leading order corrections to the leading power contribution numerically offset the subleading-power corrections to a certain extent, and our numerical results are consistent with those of previous studies on sum rules. A comparison between our results and existing model-dependent estimations is also made.     

Form factors of γ * ρ → π and γ * γ → π 0 transitions and light-cone sum rules

The method of light-cone QCD sum rules is applied to the calculation of the form factors of and transitions. We consider the dispersion relation for the amplitude in the variable . At large virtualities and , this amplitude is calculated in terms of light-cone wave functions of the pion. As a next step, the light-cone sum rule for the form factor is derived. This sum rule, together with the quark-hadron duality, provides an estimate of the hadronic spectral density in the dispersion relation. Finally, the form factor is obtained taking the limit in this relation. Our predictions are valid at and have a correct asymptotic behaviour at large . Received: 16 January 1998 / Revised version: 14 May 1998 / Published online: 26 August 1998     

Analysis of the decay B^0→Xc1π^0 with light-cone QCD sum rules

In this article, we calculate the contribution from the nonfactorizable soft hadronic matrix element to the decay B^0→Xc1π^0 with the light-cone quantum chromo-dynamic （QCD） sum rules. The numerical results show that its contribution is rather large and should not be neglected. The total amplitudes lead to a branching fraction which is in agreement with the experimental data marginally.     

Constraints on the leading-twist pion distribution amplitude from a QCD light-cone sum rule with chiral current

We study our non-perturbative formalism to describe scalar gauge-invariant metric fluctuations by extending the Ponce de León metric.     

Analysis of the coupling constants ga0ηπ0 and ga0η＇ π0 with light-cone QCD sum rules

In this article, we take the point of view that the light scalar meson a0（980） is a conventional qqstate, and calculate the coupling constants ga0ηπ0 and ga0ηπ0 with the light-cone QCD sum rules. The central value of the coupling constant ga0ηπ0 is consistent with that extracted from the radiative decay φ（1020） → a0（980）γ→ηπ0γ. The central value and lower bound of the decay width Γa0→ηπ0 =127＋8448 MeV are compatible with the experimental data of the total decay width Γa0（980） = （50-100） MeV from the Particle Data Group with a very model dependent estimation （the decay width can be much larger）, while the upper bound is too large. We give a possible explanation for the discrepancy between the theoretical calculation and experimental data.     

Determination of the constantg ωρπ from QCD sum rules

The ωρπ coupling constant is calculated using a modified form of sum rules for the vertex function 〈0|T(J _μ(x),J _ν(0))|π〉 accounting for the axial anomaly. The resultg _ωρπ=16 GeV^?1 is in good agreement with the estimates of the Vector Meson Dominance model. We show that the standard procedure gives forg _ωρπ a considerably smaller value compared to the experimental number.     

Meson-photon transition form factors and resonance cross-sections in e+e− collisions

Meson-photon-photon transition form factors for S-, P-, and D-wave states are calculated, the meson being treated as a non-relativistic heavy-quark-antiquark pair. The full dependence on both photon virtualities is included. Cross-section formulas for charge-conjugation even mesons with J^p = 0⁻, 0⁺, 1⁺, 2⁺, and 2⁻ in electron-positron collisions are presented and numerical results for LEP energies are given. In particular, we find two-photon event rates for χ_c1, η_c(2S), and η_b(1S) within reach of LEP.With minor modifications to incorporate SU(3)-flavour breaking we estimate rates for 18 light mesons as well, based on the observation that their two-photon decay widths agree remarkably well with measured data. Finally we point out that e⁺e⁻ cross sections for 1⁺ states do not vanish at low Q², the Landau-Yang suppression factors of the two-photon cross sections being compensated by the photon propagators.