arXiv subjects
Publications and source records attributed to Qing Wang.
The normal part of the Gasser-Leutwyler formulation of the chiral Lagrangian is formally derived from the first principles of QCD without taking approximations. All the coefficients are expressed in terms of certain Green's functions in QCD, which can be regarded as the general QCD definitions of the normal part of the coefficients. The approximate values of the coefficients are also presented.
Taking the sum rule for the rho meson as an example, we study the possibility of explaining the phenomenological enhamcement factors for certain terms in the vacuum expectation value of the operator product expansion in the QCD sum rule. We take a QCD motivated extended Nambu-Jona-Lasinio (ENJL) model as the low energy effective Lagrangian for QCD with which we calculate the nonperturbative contributions to the vacuum condensate expansion to obtain the enhancement factors. Our result shows that such nonperturbative contributions can cause large enough enhancement factors which can be consistent with the phenomenological values.
By introducing auxiliary fields, which by their quantum numbers vanish in perturbation theory, we relate the dynamical perturbation theory of Pagels and Stokar and a successful gauged nonlocal constituent quark model to $U(N)$ gauge theory and to QCD. This sheds light on the duality between quark models and resonance models. We then derive the effective action in the loop expansion without dropping cubic and quartic gluon couplings.
The fermion four-point functions and condensates as the chiral symmetry order parameters are calculated analytically in U(1) gauge theory in the massless phase. It is shown that in leading order of the loop expansion of the effective action, there is a critical coupling for the nonperturbative parity-invariant chirality-changing four-fermion functions; this critical coupling however is the same as that for dynamical mass generation. Therefore there is no breaking of chiral symmetry through the condensation of four-fermion functions below the critical coupling for dynamical mass generation for the fermions.
The four-quark condensates appearing in QCD sum rule are calculated nonperturbatively in a realistic QCD motivated extended Nambu-Jona-Lasinio model. The calculation is in the framework of the effective potential for local composite operators up to next-to-the-leading order in the 1/N expansion in which the non-factorized parts of the condensates are included. We show in this paper the possibility of explaining the phenomenological enhancement factor $~κ=2.4~$, needed for fitting the data in the factorization approximation, as the contribution of the non-factorized parts of the four- quark condensates.