In multiquark correlator analyses with 1/Nc classifications, it is possible to separate the scattering background and to justify the factorization of condensates, which allows us to achieve an isolated peak saturation in the QCD sum rules for multiquark currents. Then we can extract leading Nc properties of the ground state. An application to the sigma meson is demonstrated.
We give a brief overview on the present status of Generalized Vector Dominance as appplied to vector-meson production and the total photoabsorption cross section in the region of small x_{bj}. We comment on how GVD originates from QCD notions such as color transparency.
A current-current correlator with the quantum numbers of the omega meson is studied in a nuclear medium. Using weighted finite energy sum rules and dispersion relations for the current-nucleon forward scattering amplitude it is shown that strict vector meson dominance and QCD sum rules are incompatible with each other. This implies that at least one of these concepts -- which are both very powerful in the vacuum -- has to fade in the nuclear environment.
We provide a formulation of generalised vector dominance (GVD) for low-x deep-inelastic scattering that explicitly incorporates the $γ^{\ast} \to q{\bar q}$ transition and a QCD-inspired ansatz for the $(q{\bar q})p$ forward-scattering amplitude. The destructive interference originally introduced in off-diagonal GVD is recovered in the present formulation and traced back to the generic structure of two-gluon-exchange as incorporated into the notion of colour transparency. Asymptotically, the transverse photoabsorption cross section behaves as (ln Q^2)/Q^2, implying a logarithmic violation of s…
Monopole dominance for the nonperturbative features in QCD is studied both in the continuum and the lattice gauge theories. First, we study the dynamical chiral-symmetry breaking (D$χ$SB) in the dual Higgs theory using the effective potential formalism. We find that the main driving force for D$χ$SB is brought from the confinement part in the nonperturbative gluon propagator rather than the short-range part, which means monopole dominance for D$χ$SB. Second, the correlation between instantons and QCD-monopoles is studied. In the Polyakov-like gauge, where $A_4(x)$ is diagonalized, the QCD-mono…
A Finite Energy QCD sum rule at non-zero temperature is used to determine the $q^2$- and the T-dependence of the $ρππ$ vertex function in the space-like region. A comparison with an independent QCD determination of the electromagnetic pion form factor $F_π$ at $T \neq 0$ indicates that Vector Meson Dominance holds to a very good approximation at finite temperature. At the same time, analytical evidence for deconfinement is obtained from the result that $g_{ρππ}(q^{2},T)$ vanishes at the critical temperature $T_c$, independently of $q^{2}$. Also, by extrapolating the $ρππ$ form factor to $q^2 =…
We review the generalized vector dominance (GVD) approach to DIS at small values of the scaling variable, x. In particular, we concentrate on a recent formulation of GVD that explicitly incorporates the configuration of the gamma^* -> q qbar transition and a QCD-inspired ansatz for the (qqbar)p scattering amplitude. The destructive interference, originally introduced in off-diagonal GVD is traced back to the generic strcuture of two-gluon exchange. Asymptotically, the transverse photoabsorption cross section behaves as (ln Q^2)/Q^2, implying a logarithmic violation of scaling for F_2, while th…
The total photoabsorption cross section on the nucleon is studied using nondiagonal GVDM. Vector meson-nucleon scattering amplitudes are calculated in two-gluon exchange approximation of QCD. The off-diagonal transitions of diffraction dissociation type between different vector mesons and their contributions to the expression for the total photoabsorption cross section on the nucleon are also calculated. It is shown that destructive interference of diagonal and off-diagonal terms is not effective. The main conclusion is that a p-cut-off in gamma-quark antiquark transition is necessary for obta…
The infinite tower of vector mesons encoded in holographic dual QCD bring drastic changes to the soliton structure of the nucleon. The nucleon is given by a point-like instanton in 5D surrounded by a vector meson cloud with the vector dominance restored by the infinite tower. I discuss the possible relevance of this structure in hot and dense hadronic matter.
We establish a relation between the two-point field strength correlator in QCD and the dual field propagator of the effective dual Abelian Higgs model describing the infrared behaviour of QCD.
The exclusive reaction of rho meson pair electroproduction in gamma*gamma* collisions is a nice place to study various dynamics and factorization properties in the perturbative sector of QCD. At low energy (quarks dominance), this process can be considered as a way to explore QCD factorizations involving generalized distribution amplitudes (GDA) and transition distribution amplitudes (TDA), and, in the Regge limit of QCD (gluons dominance), it seems to offer a promising probe of the BFKL resummation effects which could be studied at the next international linear collider (ILC).
We present the first study of the Abelian-projected gluonic-excitation energies for the static quark-antiquark (Q$\bar{\rm Q}$) system in SU(3) lattice QCD at the quenched level, using a $32^4$ lattice at $β= 6.0$. We investigate ground-state and three excited-state Q$\bar{\rm Q}$ potentials, using smeared link variables on the lattice. We find universal Abelian dominance for the quark confinement force of the excited-state Q$\bar{\rm Q}$ potentials as well as the ground-state potential. Remarkably, in spite of the excitation phenomenon in QCD, we find Abelian dominance for the first gluonic-e…
We further explore a recent proposal that the vector mesons in QCD have a special role as Chern-Simons fields on various QCD objects such as domain walls and the one flavored baryons. We compute contributions to domain wall theories and to the baryon current coming from a generalized Wess-Zumino term including vector mesons. The conditions that lead to the expected Chern-Simons terms and the correct spectrum of baryons, coincide with the conditions for vector meson dominance. This observation provides a theoretical explanation to the phenomenological principle of vector dominance, as well as a…
To check the dual superconductor picture for the quark-confinement mechanism, we evaluate monopole dominance as well as Abelian dominance of quark confinement for both quark-antiquark and three-quark systems in SU(3) quenched lattice QCD in the maximally Abelian (MA) gauge. First, we examine Abelian dominance for the static $Q\bar Q$ system in lattice QCD with various spacing $a$ at $β$=5.8-6.4 and various size $L^3$x$L_t$. For large physical-volume lattices with $La \ge$ 2fm, we find perfect Abelian dominance of the string tension for the $Q\bar Q$ systems: $σ_{Abel} \simeq σ$. Second, we acc…
We explain that the generalized vector meson dominance (GVMD) model is successful in describing hard high energy processes because it contains expected in QCD Color Coherent Phenomena. Within the model, which reproduces Bjorken scaling and nuclear shadowing for deep inelastic processes, we calculate $P_γ(σ,Q^2)$, the probability for the photon to interact with a target with the cross section $σ$. We find that within the GVMD model the virtual photon has two main components: the ''hard'' one with the small cross section of the order of $1/Q^2$ and the high probability and the ''soft'' one with …
The vector manifestation (VM) is a new pattern for realizing the chiral symmetry in QCD. In the VM, the massless vector meson becomes the chiral partner of pion at the critical point, in contrast with the restoration based on the linear sigma model. Including the intrinsic temperature dependences of the parameters of the HLS Lagrangian determined from the underlying QCD through the Wilsonian matching together with the hadronic thermal corrections, we present a new prediction of the VM on the direct photon-$π$-$π$ coupling which measures the validity of the vector dominance (VD) of the electrom…
Values for the cross sections $σ^{ΨN}_{tot}$ and $σ^{Ψ' N}_{tot}$ are of crucial importance, once one wants to understand nuclear suppression of $J/Ψ$($Ψ'$) in a search for the quark gluon plasma. Quoted values are usually extracted from $γN \to J/Ψ(Ψ') N$ data via the vector dominance model (VDM) and are very small compared with expectations from QCD. The validity of QCD is questioned. When the VDM is extended to a multi-channel case, the $γN$ data lead to a value $2.8\pm 0.12 mb <σ_{tot}^{ΨN}(\sqrt{s}= 10 GeV) < 4.1\pm 0.15 mb$, which is a factor 3 larger than the VDM prediction. Errors are …
We propose detailed tests of the handbag approximation in exclusive deeply virtual Compton scattering. Those tests make no use of any prejudice about parton correlations in the proton which are basically unknown objects and beyond the scope of perturbative QCD. Since important information on the proton substructure can be gained in the regime of light cone dominance we consider that such a class of tests is of special relevance.
In the context of the dual superconductor picture for the confinement mechanism, we study maximally Abelian (MA) projection of quark confinement in SU(3) quenched lattice QCD with $32^4$ at $β$=6.4 (i.e., $a \simeq$ 0.058 fm). We investigate the static quark-antiquark potential $V(r)$, its Abelian part $V_{\rm Abel}(r)$ and its off-diagonal part $V_{\rm off}(r)$, respectively, from the on-axis lattice data. As a remarkable fact, we find almost perfect Abelian dominance for quark confinement, i.e., $σ_{\rm Abel} \simeq σ$ for the string tension, on the fine and large-volume lattice. We find als…
We study the Abelian projection of quark confinement in SU(3) quenched lattice QCD, in terms of the dual superconductor picture. In the maximal Abelian gauge, we perform the Cartan decomposition of the non-Abelian gauge field on a $32^4$ lattice with spacing $a \simeq0.058, 0.10$ fm (i.e., $β=6.4, 6.0$), and investigate the interquark potential $V(r)$, the Abelian part $V_{\mathrm{Abel}}(r)$, and the off-diagonal part $V_{\mathrm{off}}(r)$. For the potential analysis, we use both on-axis data and several types of off-axis data, with larger numbers of gauge configurations. Remarkably, we find a…
In SU(3) lattice QCD formalism, we propose a method to extract gauge fields from link-variables analytically. With this method, we perform the first study on effective mass generation of off-diagonal gluons and infrared Abelian dominance in the maximally Abelian (MA) gauge in the SU(3) case. Using SU(3) lattice QCD, we investigate the propagator and the effective mass of the gluon fields in the MA gauge with U(1)$_3 \timesU(1)_8$ Landau gauge fixing. The Monte Carlo simulation is performed on $16^4$ at $β$=5.7, 5.8 and 6.0 at the quenched level. The off-diagonal gluons behave as massive vector…
The low-lying eigenmodes of the Dirac operator associated with typical gauge field configurations in QCD encode, among other low-energy properties, the physics behind the solution to the $U_A(1)$ problem (i.e. the origin of the $η'$ mass), the nature of spontaneous chiral symmetry breaking, and the physics of string-breaking, quark-antiquark pair production, and the OZI rule. Moreover, the space-time chiral structure of these eigenmodes reflects the space-time topological structure of the underlying gauge field. We present evidence from lattice QCD on the local chiral structure of low Dirac ei…
A new relation between $ρ$-meson mass, weak $π$-meson decay constant, quark and gluon condensates is derived from the QCD sum rules. As a byproduct an explanation for the dominance of $ρρ$-decay for the $f_0(1370)$-meson is proposed.
We adopt the vector-meson-dominance approach to investigate Q^2-evolution of N-R transition form factors (N denotes nucleon and R an excited resonance) in the first and second resonance regions. The developed model is based upon conventional NRγ-interaction Lagrangians, introducing three form factors for spin-3/2 resonances and two form factors for spin-1/2 nucleon excitations. Lagrangian form factors are expressed as dispersionlike expansions with four or five poles corresponding to the lowest excitations of the mesons ρ(770) and ω(782). Correct high-Q^2 form factor behavior predicted by pert…
We employ QCD sum rules to calculate the coupling constant g$_{ρσγ}$ by studying the three point ${ρσγ}$-correlation function. Our results is consistent with the value of this coupling constant obtained using vector meson dominance of the electromagnetic current and the experimental $ρ^0$-photoproduction data.
We reveal the full phase structure of the effective field theory for QCD, based on the hidden local symmetry (HLS) through the one-loop renormalization group equation including quadratic divergences. We then show that vector dominance (VD) is not a sacred discipline of the effective field theory but rather an accidental phenomenon peculiar to three-flavored QCD. In particular, the chiral symmetry restoration in HLS model takes place in a wide phase boundary surface, on which the VD is realized nowhere. This suggests that VD may not be valid for chiral symmetry restoration in hot and/or dense Q…
We report on an instanton-based analysis of the gluon Green functions in the Landau gauge for low momenta; in particular we use lattice results for $α_s$ in the symmetric momentum subtraction scheme (${\rm MOM}$) for large-volume lattice simulations. We have exploited quenched gauge field configurations, $N_f=0$, with both Wilson and tree-level Symanzik improved actions, and unquenched ones with $N_f=2+1$ and $N_f=2+1+1$ dynamical flavors (domain wall and twisted-mass fermions, respectively). We show that the dominance of instanton correlations on the low-momenta gluon Green functions can be a…
A thermal Finite Energy QCD Sum Rule is used to determine the temperature behaviour of the $ωρπ$ strong coupling. This coupling decreases with increasing $T$ and vanishes at the critical temperature, a likely signal for quark deconfinement. This is then used in the Vector Meson Dominance (VMD) expression for the $π^0 \to γγ$ amplitude, which is also found to vanish at the critical temperature, as expected. This result supports the validity of VMD at $T \neq 0$. However, if VMD would not hold at finite temperature, then there is no prediction for the $π^0 \to γγ$ amplitude.
We present a simple way of separating the overlap between the soft and collinear factorization formulae of QCD squared matrix elements. We check its validity explicitly for single and double unresolved emissions of tree-level processes. The new method makes possible the definition of helicity-dependent subtraction terms for regularizing the real contributions in computing radiative corrections to QCD jet cross sections. This implies application of Monte Carlo helicity summation in computing higher order corrections.
The QCD analysis of deep inelastic diffractive scattering at HERA is performed assuming the dominance of the "soft" pomeron exchange and simple, physically motivated parametrization of parton distributions in the pomeron. Both the LO and NLO approximations are considered and the theoretical predictions concerning the quantity $R=F_L^D/F_T^D$ for diffractive structure functions are presented.
Using the light cone QCD Sum Rules Method, we study the rare B -> nu barnu gamma decay and and find that the branching ratios are, B(B_s -> nu barnu gamma) = 7.5 10^{-8}, B(B_d -> nu -> nu gamma) = 4.2 10^{-9}. A comparision of our results, on branching ratio, with constituent quark and pole dominance model predictions are presented.
We prove Abelian magnetic monopole dominance in the string tension of QCD. Abelian and monopole dominance in low energy physics of QCD has been confirmed for various quantities by recent Monte Carlo simulations of lattice gauge theory. In order to prove this dominance, we use the reformulation of continuum Yang-Mills theory in the maximal Abelian gauge as a deformation of a topological field theory of magnetic monopoles, which was proposed in the previous article by the author. This reformulation provides an efficient way for incorporating the magnetic monopole configuration as a topological n…
We investigate gluon propagators and the effective mass of the gluon fields in the MA gauge with U(1)$_3 \times$ U(1)$_8$ Landau gauge fixing in SU(3) lattice QCD. The Monte Carlo simulation is performed on $16^4$ at $β$=5.7, 5.8 and 6.0 and $32^4$ at $β=$5.8 and 6.0 at the quenched level. To calculate the propagators, we adopt a method to extract gauge fields from link-variables analytically in the SU(3) case. The off-diagonal gluons behave as massive vector bosons with the approximate effective mass $M_{\rm off} \simeq 1.1 - 1.2 {\rm GeV}$ in the region of $r = 0.3 - 0.8 {\rm fm}$, and the p…
We investigate the semileptonic decays of B and D mesons into $π$ and $ρ$ mesons, respectively, by means of QCD sum rules. We find that for the vector formfactors involved the pole dominance hypothesis is valid to good accuracy with pole masses in the expected range. Pole dominance, however, does not apply to the axial formfactors which results in specific predictions for the predominant polarization of the $ρ$ meson and the shape of the lepton spectrum. For the total decay rates we find $Γ(\bar B^0 \to π^+ e^- \barν) = (5.1\pm 1.1)\,|V_{ub}|^2\, 10^{12}\,{\rm s^{-1}}$, $Γ( D^0 \to π^- e^+ ν) …
In this article, we analyze the vertex $D^*D^*ρ$ with the light-cone QCD sum rules. The strong coupling constant $g_{D^*D^*ρ}$ is an important parameter in evaluating the charmonium absorption cross sections in searching for the quark-gluon plasmas. Our numerical value for the $g_{D^*D^*ρ}$ is consistent with the prediction of the effective SU(4) symmetry and vector meson dominance theory.
The QCD analysis of deep inelastic diffractive scattering is performed assuming the dominance of the "soft" pomeron exchange and simple, physically motivated parametrization of parton distributions in a pomeron. Results of the analysis are compared with the recent data obtained by the H1 collaboration at HERA. Both the LO and NLO approximations are considered and the theoretical predictions concerning the quantity $R=F_L^D/F_T^D$ for diffractive structure functions are presented.
Vector Meson Dominance ideas together with a Finite Energy QCD sum rule allows for the determination of the $q^{2}$- and the $T$- dependence of the effective hadronic coupling constant $g_{ρππ}$ in the space-like region. It turns out that $g_{ρππ}(q^{2},T)$ vanishes at the critical temperature $T_{c}$, independently of $q^{2}$. A comparison with a previous independent QCD determination of the electromagnetic pion form factor at finite temperature supports the validity of Vector Meson Dominance at finite temperature. We find also thet the pion radius increases with $T$, having a divergent behav…
Starting from the QCD Lagrangian and the surface tension of QCD bubbles we derive the critical size of bubbles, the nucleation probability and the nucleation site separation distance. We find the separation of sites is more than an order of magnitude larger than previous QCD model estimates, which could lead to observable effects.
We briefly review the QCD physics and then introduce recent topics on the confinement physics. In the maximally abelian (MA) gauge, the low-energy QCD is abelianized owing to the effective off-diagonal gluon mass $M_{\rm off} \simeq 1.2 {\rm GeV}$ induced by the MA gauge fixing. We demonstrate the construction of the dual Ginzburg-Landau (DGL) theory from the low-energy QCD in the MA gauge in terms of the lattice QCD evidences on infrared abelian dominance and infrared monopole condensation.
The nondiagonal generalized vector dominance model (GVDM) of photoabsorption is elaborated using QCD-motivated picture of the (gamma)-(q,anti q) - transition and subsequent meson dominated scattering of the (q, anti q)-pair on the nucleon. The relativistic constituent quark model for a description of the meson (q, anti q)-wave functionsis used. The meson-nucleon scattering is calculated in the two-gluon exchange approximation. It is shown that the destructive interference effects and corresponding cancellations in the photoabsorption cross section formula are small, so the GVDM predictions are…
We discuss applications of QCD sum rules on the light-cone to the form factors of the exclusive transitions $B \rightarrow π$ and $D\rightarrow π$, and to the $B^*B π$ and $D^*D π$ coupling constants. In the light of our results we examine the pole dominance model for these form factors. A first estimate is given on the nonfactorizable amplitude of the decay $ B \ra J/ψK$.
We argued that deep inelastic scattering (DIS) at small values of Q squared is an essentially nonperturbative process and can be described, partially at least, by the vector meson dominance (VMD) model. We showed by the straightforward calculation that VMD model alone can successfully explain data on structure functions of DIS in a broad interval of x (5e-2 - 1e-4) for the region Q squared < 1 GeV squared. For a description of data at larger Q squared we used the two-component (VMD + perturbative QCD) approach. We showed that these two components can be separated if VMD is used in the aligned …
We investigate the properties of quarks and gluons above the chiral phase transition temperature $T_c,$ using the RG improved gauge action and the Wilson quark action with two degenerate quarks mainly on a $32^3\times 16$ lattice. In the one-loop perturbation theory, the thermal ensemble is dominated by the gauge configurations with effectively $Z(3)$ center twisted boundary conditions, making the thermal expectation value of the spatial Polyakov loop take a non-trivial $Z(3)$ center. This is in agreement with our lattice simulation of high temperature QCD. We further observe that the temporal…
Using the QCD {\it hybrid} (moments-Laplace) sum rule, we show $semi$-$analytically$ that, in the limit $M_b \rar \infty$, the $q^2$ and $M_b$ behaviours of the heavy-to-light exclusive ($\bar B\rar ρ~(π)$ semileptonic as well as the $ B\rar ργ$ rare) decay--form factors are $universally$ dominated by the contribution of the soft light-quark condensate rather than that of the hard perturbative diagram. The QCD-analytic $q^2$ behaviour of the form factors is a polynomial in $q^2/M^2_b$, which mimics quite well the usual pole parametrization, except in the case of the $A_1^B$ form factor, where …
In this article, we calculate the strong coupling constants of the $ρNN$, $ρΣΣ$ and $ρΞΞ$ in the framework of the light-cone QCD sum rules approach. The strong coupling constants of the meson-baryon-baryon are the fundamental parameters in the one-boson exchange model which describes the baryon-baryon interactions successfully. The numerical values are in agreement with the existing calculations in part. The electric and magnetic $F/(F+D)$ ratios deviate from the prediction of the vector meson dominance theory, the SU(3) symmetry breaking effects are very large.
I discuss QCD sum rules determinations of the form factors governing the decay $B \to π(ρ) \ell ν$. For some of these form factors the computed dependence on the momentum transferred does not agree with the expectation from the nearest pole dominance hypothesis. Relations are observed among the form factors, that seem to be compatible with equations recently derived by B.Stech. The measurement of a number of color suppressed nonleptonic B decay rates could shed light on the accuracy of the calculation of these form factors and on the factorization approximation.
The QCD-based generalized vector dominance-color-dipole picture (GVD-CDP) provides a coherent picture of low-x DIS, deeply virtual Compton scattering and light as wel as heavy vector-meson production.
In this article, we assume that there exists a scalar $D_s^\ast {\bar D}_s^\ast$ molecular state in the $J/ψϕ$ invariant mass distribution, and study its mass using the QCD sum rules. The predictions depend heavily on the two criteria (pole dominance and convergence of the operator product expansion) of the QCD sum rules. The value of the mass is about $M_{D_s^\ast {\bar D}_s^\ast}=(4.43\pm0.16) \rm{GeV}$, which is inconsistent with the experimental data. The $D_s^\ast {\bar D}_s^\ast$ is probably a virtual state and not related to the meson Y(4140). Other possibility, such as a hybrid charmon…
We investigate the photon structure functions at small Bjorken variable $x$ in the framework of the holographic QCD, assuming dominance of the Pomeron exchange. The quasi-real photon structure functions are expressed as convolution of the Brower-Polchinski-Strassler-Tan (BPST) Pomeron kernel and the known wave functions of the U(1) vector field in the five-dimensional AdS space, in which the involved parameters in the BPST kernel have been fixed in previous studies of the nucleon structure functions. The predicted photon structure functions, as confronted with data, provide a clean test of the…
We provide a method to study hadronic matter at finite density in the context of the Sakai-Sugimoto model. We introduce the baryon chemical potential through the external $U(1)_v$ in the induced (DBI plus CS) action on the D8-probe-brane, where baryons are skyrmions. Vector dominance is manifest at finite density. We derive the baryon density effect on the energy density, the dispersion relations of pion and vector mesons at large $N_c$. The energy density asymptotes to a constant at large density suggesting that dense matter at large $N_c$ freezes, with the pion velocity dropping to zero. Hol…
We show that off-diagonal gluons and off-diagonal ghosts acquire their masses dynamically in QCD if the maximal Abelian gauge is adopted. This result strongly supports the Abelian dominance in low-energy region of QCD. The mass generation is shown to occur due to ghost-anti-ghost condensation caused by attractive quartic ghost interactions within the Abelian projected effective gauge theory (derived by one of the authors). In fact, the quartic ghost interaction is indispensable for the renormalizability due to nonlinearity of the maximal Abelian gauge. The ghost-anti-ghost condensation is asso…
We study abelian dominance and monopole condensation for the quark confinement physics using the lattice QCD simulations in the MA gauge. These phenomena are closely related to the dual superconductor picture of the QCD vacuum, and enable us to construct the dual Ginzburg-Landau (DGL) theory as an useful effective theory of nonperturbative QCD. We then apply the DGL theory to the studies of the low-lying hadron structure and the scalar glueball properties.
We discuss the pion and nucleon form factors and generalized form factors within the large-Nc approach in the space-like region. We estimate their theoretical uncertainties through the use of the half-width rule, amounting to taking the half-width of the resonances as the deviation of their mass parameters. The approach embodies the meson dominance of form factors and the high-energy constraints from perturbative QCD. We compare the results with the available experimental data and lattice simulations. The meson-dominance form factors are generally comparable to the available experimental data …
The vector dominance of the electromagnetic form factors both for mesons and baryons arises naturally in holographic QCD, where both the number of colors and the 't Hooft coupling are taken to be very large, offering a bona-fide derivation of the notion of vector dominance. The crucial ingredient for this is the infinite tower of vector mesons in the approximations made which share features that are characteristic of the quenched approximation in lattice QCD. We approximate the infinite sum by contributions from the lowest four vector mesons of the tower which turn out to saturate the charge a…
The $πNN$ form factor $g_{πNN}(q^2)$ is obtained from a quenched lattice QCD calculation of the pseudoscalar form factor $g_P(q^2)$ of the proton with pion pole dominance. We find that $g_{πNN}(q^2)$ fitted with the monopole form agrees well with the Goldberger-Treiman relation and is much preferred over the dipole form. The monopole mass is determined to be $0.75 \pm 0.14 {\rm GeV}$ which shows that $g_{πNN}(q^2)$ is rather soft. The extrapolated $πN$ coupling constant $g_{πNN} = 12.7 \pm 2.4$ is quite consistent with the phenomenological values. We also compare $g_{πNN}(q^2)$ with the axial …
The static QCD potential is analyzed in operator-product-expansion within potential-NRQCD framework when r << 1/Lambda_{QCD}. We show that the leading short-distance contribution to the potential, defined as a perturbatively computable Wilson coefficient, can be expressed, up to O(r^2), as a ``Coulomb+linear'' potential. It coincides with the ``Coulomb+linear'' potential obtained previously from the renormalon-dominance hypothesis. Non-perturbative contributions are of order r^2 and subleading.
