Critical behavior of J/ψ across the phase transition from QCD sum rules

We study behavior of J/ψ in hot gluonic matter using QCD sum rules. Taking into account temperature dependences of the gluon condensates extracted from lattice thermodynamics for the pure SU(3) system, we find that the mass and width of J/ψ exhibit rapid change across the critical temperature.     

A comprehensive revisit of the ρ meson with improved Monte-Carlo based QCD sum rules

We improve the Monte-Carlo based QCD sum rules by introducing the rigorous H¨older-inequalitydetermined sum rule window and a Breit-Wigner type parametrization for the phenomenological spectral function.In this improved sum rule analysis methodology, the sum rule analysis window can be determined without any assumptions on OPE convergence or the QCD continuum. Therefore, an unbiased prediction can be obtained for the phenomenological parameters(the hadronic mass and width etc.). We test the new approach in the ρ meson channel with re-examination and inclusion of α_s corrections to dimension-4 condensates in the OPE. We obtain results highly consistent with experimental values. We also discuss the possible extension of this method to some other channels.     

Calculation of the axial form factor of the decay π → evγ by means of QCD sum rules

The axial form factor of the decay π → evγ is calculated by means of QCD sum rules, using the experimental value for the mean- squared charge radius of the pion. The ratio of the axial to vector form factor is predicted to be γ = 0.42±0.2.     

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.     

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.     

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).     

Magnetic moment of the pentaquark Θ+(1540) as diquark-diquark-antiquark state with QCD sum rules

In this article, we study the magnetic moment of the pentaquark state Θ⁺(1540) as a diquark-diquark-antiquark ( ) state with the QCD sum rules in an external weak electromagnetic field (EFSR) and the light-cone QCD sum rules (LCSR) respectively. The numerical results indicate that the magnetic moment is about for the EFSR and - for the LCSR. As the values obtained from the EFSR are more stable than the corresponding ones from the LCSR, is more reliable. Received: 29 March 2005, Revised: 28 June 2005, Published online: 21 October 2005 PACS: 12.38.Aw, 12.38.Lg, 12.39.Ba, 12.39.-x     

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.     

Analysis of the 1S and 2S states of AQ and ΘQ with QCD sum rules

In this article,we study the ground states and the first radial excited states of the flavor antitriplet heavy baryon states AQ and ΘQ with the spin-parity JP =...     

Local-duality QCD sum rules for strong isospin breaking in the decay constants of heavy–light mesons

We discuss the leptonic decay constants of heavy–light mesons by means of Borel QCD sum rules in the local-duality (LD) limit of infinitely large Borel mass parameter. In this limit, for an appropriate choice of the invariant structures in the QCD correlation functions, all vacuum-condensate contributions vanish and all nonperturbative effects are contained in only one quantity, the effective threshold. We study properties of the LD effective thresholds in the limits of large heavy-quark mass \(m_Q\) and small light-quark mass \(m_q\). In the heavy-quark limit, we clarify the role played by the radiative corrections in the effective threshold for reproducing the pQCD expansion of the decay constants of pseudoscalar and vector mesons. We show that the dependence of the meson decay constants on \(m_q\) arises predominantly (at the level of 70–80%) from the calculable \(m_q\)-dependence of the perturbative spectral densities. Making use of the lattice QCD results for the decay constants of nonstrange and strange pseudoscalar and vector heavy mesons, we obtain solid predictions for the decay constants of heavy–light mesons as functions of \(m_q\) in the range from a few to 100 MeV and evaluate the corresponding strong isospin-breaking effects: \(f_{D^+} - f_{D^0}=(0.96 \pm 0.09) \ \mathrm{MeV}\), \(f_{D^{*+}} - f_{D^{*0}}= (1.18 \pm 0.35) \ \mathrm{MeV}\), \(f_{B^0} - f_{B^+}=(1.01 \pm 0.10) \ \mathrm{MeV}\), \(f_{B^{*0}} - f_{B^{*+}}=(0.89 \pm 0.30) \ \mathrm{MeV}\).     

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.     

QCD sum rule analysis of the coupling constant g ωσγ

We employ QCD sum rules to calculate the coupling constant g by studying the three point -correlation function. Our result complements the analysis of this coupling constant utilizing the experimental value of the ⁰⁰ decay rate studied within the framework of chiral perturbation theory including vector meson and meson intermediate states.     

Analysis of the ΛQ baryons in the nuclear matter with the QCD sum rules

In this article, we study the Λ c and Λ b baryons in the nuclear matter using the QCD sum rules, and obtain the in-medium masses M\varLambda c*=2.335 GeVM_{\varLambda _{c}}^{*}=2.335~\mathrm{GeV}, M\varLambda b*=5.678 GeVM_{\varLambda _{b}}^{*}=5.678~\mathrm{GeV}, the in-medium vector self-energies \varSigma \varLambda cv=34 MeV\varSigma ^{\varLambda _{c}}_{v}=34~\mathrm{MeV}, \varSigma \varLambda bv=32 MeV\varSigma ^{\varLambda _{b}}_{v}=32~\mathrm {MeV}, and the in-medium pole residues l\varLambda c*=0.021 GeV3\lambda_{\varLambda _{c}}^{*}=0.021~\mathrm{GeV}^{3}, l\varLambda b*=0.026 GeV3\lambda_{\varLambda _{b}}^{*}=0.026~\mathrm{GeV}^{3}. The mass-shifts are M\varLambda c*-M\varLambda c=51 MeVM_{\varLambda _{c}}^{*}-M_{\varLambda _{c}}=51~\mathrm{MeV} and M\varLambda b*-M\varLambda b=60 MeVM_{\varLambda _{b}}^{*}-M_{\varLambda _{b}}=60~\mathrm{MeV}, respectively.