QCD sum rule for Λ(1405)

Motivated by the recently constructed interpolation field for S₁₁(1535), we propose a new interpolating field for Λ(1405). Using this current, we calculate the mass of Λ(1405) based on the conventional QCD sum rule analysis. By calculating the Wilson coefficients up to dimension 8 operators and taking into account the mass corrections from s-quark, we find the calculated mass of Λ(1405) to be very close to its experimental value.     

QCD sum rule study for hidden-strange pentaquarks

Inspired by the LHCb observations of hidden-charm \begin{document}$ P_{c(s)} $\end{document} states, we study their hidden-strange analog\begin{document}$ P_s $\end{document} states in both the \begin{document}$ [udu][\bar ss] $\end{document} and \begin{document}$ [uds][\bar su] $\end{document} configurations. We investigate \begin{document}$ P_s $\end{document} pentaquark states in the \begin{document}$ p\eta^\prime $\end{document}, \begin{document}$ p\phi $\end{document}, \begin{document}$ \Lambda K $\end{document}, \begin{document}$ \Sigma K $\end{document}, and \begin{document}$ \Sigma^\ast K^\ast $\end{document} structures with \begin{document}$J^P ={1}/{2}^-$\end{document} and \begin{document}$ \Sigma ^\ast K $\end{document} and \begin{document}$ \Sigma K^\ast $\end{document} with \begin{document}$J^P = {3}/{2}^-$\end{document} and calculate their masses in the framework of QCD sum rules. Our numerical results show that the extracted hadron masses for all the \begin{document}$ p\eta^\prime $\end{document}, \begin{document}$ p\phi $\end{document}, \begin{document}$ \Lambda K $\end{document}, \begin{document}$ \Sigma K $\end{document}, and \begin{document}$ \Sigma^\ast K^\ast $\end{document} structures are significantly higher than the \begin{document}$ \Sigma K $\end{document} mass threshold, and the masses for \begin{document}$ \Sigma ^\ast K $\end{document} and \begin{document}$ \Sigma K^\ast $\end{document}are also higher than the threshold of the corresponding hadron; hence, no bound state exists in such channels, which is consistent with the current experimental status.     

QCD sum rule for nucleon in nuclear matter

We consider the two-point function of nucleon current in nuclear matter and write a QCD sum rule to analyse the residue of the nucleon pole as a function of nuclear density. The nucleon self-energy needed for the sum rule is taken as input from calculations using phenomenological N N potential. Our result shows a decrease in the residue with increasing nuclear density, as is known to be the case with similar quantities.     

QCD analysis of the Bjorken sum rule revisited

We present extended analysis of the polarized Bjorken sum rule using the four-loop expression for the coefficient function C _Bj(α_s) available now and the recent low Q ²-data from the Jefferson Lab and COMPASS experiments. We demonstrate that the perturbative series for the function C _Bj gives a hint to its asymptotic nature manifesting itself in the region Q ² ? 1 GeV². It is confirmed by the considered integral model for the perturbative QCD correction. We analyze values of higher-twist terms extracted from the mentioned data and discuss the interplay between higher orders perturbative and higher-twist contributions. We extend our consideration to the Gross-Llewellyn Smith sum rule and investigate the relation between higher twist coefficients in these two sum rules.     

Perturbative QCD analysis of the Bjorken sum rule

We study the polarized Bjorken sum rule at low momentum transfer squared Q ² ≤ 3 GeV² in the twist-two approximation and to the next-to-next-to-leading order accuracy.     

Exclusive radiativeB-decays in the light-cone QCD sum rule approach

We discuss vector, axial-vector, scalar and pseudoscalar two-point functions at low and intermediate energies. We first review what is known from chiral perturbation theory, as well as from a heat kernel expansion within the context of an extended Nambu-Jona-Lasinio (ENJL) model. We derive then these two-point functions to all orders in the momenta and to leading order in 1/N _c within the framework of this model. We find an improved high-energy behaviour and a general way of parametrizing them that shows relations between some of the two-point functions, which are also valid in the presence of gluonic interactions. The similarity between the shape of the experimentally known spectral functions and the ones we derive, is greatly improved with respect to those predicted by the usual constituent quark like models. We also obtain the scalar massM _s =2M _Q independent of the regularization scheme. In the end, we calculate fully an example of a nonleptonic matrix element in the ENJL-model, theπ ⁺?π ⁰ electromagnetic mass difference and find good agreement with the measured value.

     

QCD sum rule view on EMC effect

Using Ioffe-time distribution calculated in the framework of QCD sum rule we analyse the difference between the valence quark structure functions of a free proton and a proton placed into nuclear matter.     

Gluon condensate from superconvergent QCD sum rule

Sum rules for the nonperturbative piece of correlators (specifically, the vector current correlator) are discussed. The sum rule subtracting the perturbative part is of the superconvergent type. Thus it is dominated by the bound states and the low-energy production cross section. It leads to a determination of the gluon condensate _sG². We find _sG²0.048±0.030 GeV⁴.     

Light four-quark states and QCD sum rule

The relations among four-quark states, diquarks and QCD sum rules are discussed. The situation of the existing, but incomplete studies of four-quark states with QCD sum rules is analyzed. Masses of some diquark clusters were attempted to be determined by QCD sum rules, and masses of some light tetraquark states were obtained in terms of the diquarks.     

Light four-quark states and QCD sum rule

The relations among four-quark states, diquarks and QCD sum rules are discussed. The situation of the existing, but incomplete studies of four-quark states with QCD sum rules is analyzed. Masses of some diquark clusters were attempted to be determined by QCD sum rules, and masses of some light tetraquark states were obtained in terms of the diquarks.     

A QCD sum rule study of the light scalar mesons

We examine the interpretation of the light scalar meson nonet as bound states of the scalar diquark and the scalar antidiquark using the QCD sum rule approach. Our results are obtained by means of the operator product expansion (OPE) including operators up to dimension 8. They show no evidence of the coupling of the tetraquark states to the light scalar meson nonet.