Abstract:
We present a construction of the pion electromagnetic form factor where the transition from large-Nc Regge vector meson dominance models with infinitely many resonances to perturbative QCD is built in explicitly. The construction is based on an appropriate assignment of residues to the Regge poles, which fulfills the constraints of the parton-hadron duality and perturbative QCD. The model contains a slowly falling off non-perturbative contribution which dominates over the perturbative QCD radiative corrections for the experimentally accessible momenta. The leading order and next-to-leading order calculations show a converging pattern which describes the available data within uncertainties, while the onset of asymptotic QCD takes place at extremely high momenta, Q ~ 10^3-10^4 GeV. The method can be straightforwardly extended to study other form factors where the perturbative QCD result is available.

Abstract:
Scalar-isoscalar states are analyzed within the large-Nc Regge approach. We find that the lightest f0(600) scalar-isoscalar state fits very well into the pattern of the radial Regge trajectory. We confirm the obtained mass values from an analysis of the pion and nucleon spin-0 gravitational form factors, recently measured on the lattice. We find that a simple two-state model suggests a meson nature of f0(600), and a glueball nature of f0(980), which naturally explains the ratios of various coupling constants. Finally, matching to the OPE requires a fine-tuned mass condition of the vanishing dimension-2 condensate in the Regge approach with infinitely many scalar-isoscalar states.

Abstract:
Scalar-isoscalar states ($J^{PC}=0^{++}$) are discussed within the large-$N_c$ Regge approach. We find that the lightest $f_0(600)$ scalar-isoscalar state fits very well into the pattern of the radial Regge trajectory where the resonance nature of the states is advantageously used. We confirm the obtained mass values from an analysis of the pion and nucleon spin-0 gravitational form factors, recently measured on the lattice. We provide arguments suggesting an alternating meson-glueball pattern of the 0++ states, which is supported by the pseudoscalar-isovector 0+- excited spectrum and asymptotic chiral symmetry. Finally, matching to the OPE requires a fine-tuned mass condition of the vanishing dimension-2 condensate in the Regge approach with infinitely many scalar-isoscalar states.

Abstract:
Exotic baryons have been predicted in the context of the chiral soliton model. These states have been identified with strangeness +1 resonances reported in a number of experiments. In this talk it is pointed out that the technique used to quantize these solitons in most conventional treatments depends on dynamical assumptions beyond those in standard large Nc physics. These additional assumptions have never been justified.

Abstract:
We discuss the phenomenological implications of assuming a Veneziano-type spectrum for the vector and axial-vector two-point functions in QCD at large Nc. We also compare the phenomenological results with those of Lowest-Meson Dominance, and find that they agree.

Abstract:
A light collective theta+ baryon state (with strangeness +1) was predicted via rigid-rotor collective quantization of SU(3) chiral soliton models. This paper explores the validity of this treatment. A number of rather general analyses suggest that predictions of exotic baryon properties based on this approximation do not follow from large Nc QCD. These include an analysis of the baryon's width, a comparison of the predictions with general large Nc consistency conditions of the Gervais-Sakita-Dashen-Manohar type; an application of the technique to QCD in the limit where the quarks are heavy; a comparison of this method with the vibration approach of Callan and Klebanov; and the 1/Nc scaling of the excitation energy. It is suggested that the origin of the problem lies in an implicit assumption in the that the collective motion is orthogonal to vibrational motion. While true for non-exotic motion, the Wess-Zumino term induces mixing at leading order between collective and vibrational motion with exotic quantum numbers. This suggests that successful phenomenological predictions of theta+ properties based on rigid-rotor quantization were accidental.

Abstract:
We show how to match quark models to the 1/Nc expansion of QCD. As an example we discuss in detail the mass operator of orbitally excited baryons and match it to the one-gluon exchange and the one-boson exchange variants of the quark model. The matching procedure is very general and makes use of the transformation properties of states and operators under S_N^{orb} \times S_N^{sp-fl}, the permutation group acting on the orbital and spin-flavor degrees of freedom of N quarks.

Abstract:
We show how to match quark models to the 1/Nc expansion of QCD. As an example we discuss in detail the mass operator of orbitally excited baryons and match it to the one-gluon exchange and the one-boson exchange variants of the quark model. The matching procedure is very general and makes use of the transformation properties of states and operators under S_N^{orb} \times S_N^{sp-fl}, the permutation group acting on the orbital and spin-flavor degrees of freedom of N quarks.