We investigate the possibility for a quark-antiquark pair to form a bound state at temperatures higher than the critical one (T > T c ), thus after deconfinement. Our main goal is to find analytical criteria constraining the existence of such mesons. Our formalism relies on a Schrödinger equation for which we study the physical consequences of using both the free energy and the internal energy as potential term, assuming a widely accepted temperature-dependent Yukawa form for the free energy and a recently proposed nonperturbative form for the screening mass. We show that using the free energy only allows for the 1S bottomonium to be bound above T c , with a dissociation temperature around 1.5 × T c . The situation is very different with the internal energy, where we show that no bound states at all can exist in the deconfined phase. But, in this last case, quasibound states could be present at higher temperatures because of a positive barrier appearing in the potential.

We establish a connection between the quark model and the 1/N c expansion mass formulas used in the description of baryon resonances. First, we show that a remarkable compatibility exists between the two methods in the light baryon sector. Second, we extend our study to the baryons made of one heavy quark and two light quarks. It appears that the band number used to classify baryons in large N c QCD is explained by the quark model, and the mass formulas for both approaches are consistent. In particular, the quark model reproduces the coefficients of the 1/N c mass formula for the ground state charm and bottom baryons with all the parameters fitted to light baryons.

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We investigate some static properties of light baryon ground states in three inequivalent large-N limits (with respect to the quark color representation): 't Hooft, QCD antisymmetric and QCD symmetric. Our framework is a constituent quark model with relativistic-type kinetic energy, stringlike confinement and one-gluon-exchange term, thus leading to well-defined results even for massless quarks. Moreover, two spin-dependent potentials are considered and treated as perturbations: the color magnetic interaction stemming from the one-gluon exchange process and the chiral (or Goldstone) boson exchange interaction. Our results confirm previous ones obtained by using either diagrammatic methods or constituent approaches for heavy quarks.Xth Quark Confinement and the Hadron Spectrum,