Matching meson resonances to OPE in QCD

We investigate the possible corrections to the linear Regge trajectories for the light-quark meson sector by matching two-point correlators of quark currents to the Operator Product Expansion. We find that the allowed modifications to the linear behavior must decrease rapidly with the principal quantum number. After fitting the lightest states in each channel and certain low-energy constants the whole spectrum for meson masses and residues is obtained in a satisfactory agreement with phenomenology. The perturbative corrections to our results are discussed.Comment: 4 pages, talk given at the First Workshop on Quark Hadron Duality and the Transition to pQCD (June 2005, Frascati, Italy) and at the International Conference on QCD and Hadronic Physics (June 2005, Beijing, China

Holographic Estimates of the Deconfinement Temperature

The problem of self-consistent estimates of the deconfinement temperature Tc in the framework of the bottom-up holographic approach to QCD is scrutinized. It is shown that the standard soft wall model gives Tc for planar gluodynamics around 260 MeV in a good agreement with the lattice data. The extensions of soft wall model adjusted for descriptions of realistic meson spectra result in a broad range of predictions. This uncertainty is related with a poor experimental information on the radially excited mesons.Comment: 19 pages, 4 figures, typos are corrected, matches the version published in Eur. Phys. J.

Lagrangian alternative to QCD string

The spectrum of radially excited hadrons provides much information about the confinement forces in QCD. The confinement is realized most naturally in terms of the QCD string whose quantization gives rise to the radially excited modes. We propose an alternative framework for the description of the excited spectrum. Namely we put forward some effective field models in which the hadrons acquire masses due to interaction with a scalar field modeling the non-perturbative gluon vacuum. The effective potential for this field is periodic with an infinite number of non-equivalent vacua. The radially excited hadrons emerge as elementary excitations over different vacua. We construct explicit examples for such effective theories in the meson sector. An interesting byproduct of the considered models is the existence of a classical field configuration in each vacuum. Depending on the model, it can represent a domain wall, Nielsen-Olesen vortex or 't Hooft-Polyakov monopole. In the pure scalar sector, it is shown that the first quantum correction leads to splitting of the radially excited modes into two nearly degenerate states. Such a phenomenon has some phenomenological support. The presented approach may be also viewed as an alternative framework to the bottom-up AdS/QCD models where the radial excitations appear on the classical level as well.Comment: 21 pages, 3 figures, accepted by Eur. Phys. J.

The masses of vector mesons in holographic QCD at finite chiral chemical potential

Central heavy-ion collisions may induce sizeable fluctuations of the topological charge. This effect is expected to distort the dispersion relation for the hadron masses. We construct a general setup for a compact description of this phenomenon in the framework of bottom-up holographic approach to QCD. A couple of soft wall holographic models are proposed for the vector mesons. The states having different circular polarizations are shown to have different effective mass. The requirement of stability imposes strong constraints on the possible choice of models.Comment: 10 page

Meson mass spectrum and OPE: matching to the large-N_c QCD

The relations between masses and decay constants of variety of meson resonances in the energy range 0--3 GeV are verified from the string-like, linear mass spectrum for vector, axial-vector, scalar and pseudoscalar mesons with a universal slope. The way to match the universality with the Operator Product Expansion (OPE) is proposed. The necessity of small deviations from linearity in parameterization of the meson mass spectrum and their decay constants is proven from matching to OPE.Comment: 4 pages, more refs added, Talk at V Int. Conference "Quark Confinement and the Hadron Spectrum", 10-14 Sept. 2002, Garda Lake, Ital