The qq spectrum is studied in a generalized constituent quark model constrained in the study of the N N phenomenology and the baryon spectrum. An overall good fit to the available experimental data is obtained. A detailed analysis of all sectors from the light-pseudoscalar and vector mesons to bottomonium is performed paying special attention to the existence and nature of some non well-established states. These results should serve as a complementary tool in distinguishing conventional quark model mesons from glueballs, hybrids or multiquark states.

Abstract. We review the application of non-relativistic constituent quark models to study one, two and three non-strange baryon systems. We present results for the baryon spectra, potentials and observables of the NN, N∆, ∆∆ and NN * (1440) systems, and also for the binding energies of three non-strange baryon systems. We make emphasis on observable effects related to quark antisymmetry and its interplay with quark dynamics.

We investigate the structure of heavy baryons containing a charm or a bottom quark. We employ a constituent quark model successful in the description of the baryon-baryon interaction which is consistent with the light baryon spectra. We solve exactly the three-quark problem by means of the Faddeev method in momentum space. Heavy baryon spectrum shows a manifest compromise between perturbative and nonperturbative contributions. The flavor dependence of the one-gluon exchange is analyzed. We assign quantum numbers to some already observed resonances and we predict the first radial and orbital excitations of all states with J = 1/2 or 3/2. We combine our results with heavy quark symmetry and lowest-order SU (3) symmetry breaking to predict the masses and quantum numbers of six still non-measured groundstate beauty baryons.

t lnstitut fiir Theoretische Phydk, University of Tobingen. D-7400 Tiibingen, Federal Republic of Germany Received I July 1993Abstrad. A modilied quarkquark interaction is applied to study lhe nucleon-nucleon interaction. The quark potential is suggested by inslanton models and includes pion (n) and sigma ( 0 ) exchanges as non-perturbative components and the one-gluon exchange as a pemrbative one. The nucleon-nucleon potential derived from this model presents short-range repulsion and mediun-range attraction besides the usual pion tail. Using this interaction the nucleon-nucleon phase shifts within the resonating group method have been olculated. They agree reasonably well with experimental values.

The recent observation at CDF and D0 of Σ b , Σ * b and Ξ b baryons opens the door to the advent of new states in the bottom baryon sector. The states measured provide sufficient constraints to fix the parameters of phenomenological models. One may therefore consistently predict the full bottom baryon spectra. For this purpose we have solved exactly the three-quark problem by means of the Faddeev method in momentum space. We consider our guidance may help experimentalists in the search for new bottom baryons and their findings will help in constraining further the phenomenological models. We identify particular states whose masses may allow to discriminate between the dynamics for the light-quark pairs predicted by different phenomenological models. Within the same framework we also present results for charmed, doubly charmed, and doubly bottom baryons. Our results provide a restricted possible assignment of quantum numbers to recently reported charmed baryon states. Some of them are perfectly described by D−wave excitations with J P = 5/2 + , as the Λ c (2880), Ξ c (3055), and Ξ c (3123).

A simple string model inspired by the strong-coupling regime of quantum chromodynamics is used as a potential for studying the spectrum of multiquark systems with two quarks and two antiquarks, with a careful treatment of the four-body problem. It is found that the ground state is stable, lying below the threshold for dissociation into two isolated mesons. DOI: 10.1103/PhysRevD.76.114013 PACS numbers: 12.39.Jh, 12.40.Yx The question of the existence of multiquark systems is almost as old as the concept of quarks, see, e.g., [1], in particular, the paper by R. H. Dalitz therein. Since the early days of hadron spectroscopy within the quark approach, many studies have been devoted to multiquark states. Of particular interest are hadrons with exotic quantum numbers that cannot be matched by any quark-antiquark (q q) or three-quark (qqq) configuration, and among them, the states, if any, which are bound below the threshold for dissociation into two ordinary hadrons and thus are narrow and should show up clearly in the experimental spectrum.The present contribution belongs to the class of constituent quark models: an explicit set of rules is adopted to mimic the interaction of quarks in quantum chromodynamics (QCD) and, within this framework, the 2-body, 3-body, and higher few-body problems are solved as accurately as possible to examine whether quarks tend to split into small (q q) and (qqq) clusters or sometimes find it energetically more favorable to form multiquark clusters. After a series of estimates within the bag model (see, e.g., [2]), there have been several attempts with potential models, using the powerful few-body techniques developed in atomic and nuclear physics.Several dynamical ingredients have been identified along the years as possible sources of multiquark binding. The best known is probably chromomagnetism [3]: the spin-color operator i ji j , which is encountered in the spin-dependent part of one-gluon exchange gives rise to remarkable coherence effects, and gives in some multiquark clusters some attraction that is larger than in its decay products. This mechanism was proposed, in particular, for the H dibaryon (uuddss) [4], tentatively below the threshold, and for the 1987 version of the heavy pentaquark (Q q q q q ) [5]. The chromomagnetic scenario has, however, difficulties: the first optimistic predictions carried out in the limit of exact flavor SU(3) symmetry, and using short-range correlation coefficients borrowed from ordinary hadrons, do not survive a more careful dynamical treatment [6].Another binding mechanism is based on the flavor independence of the confining interaction. In a given static potential Vr 1 ; . . ., the asymmetric mass configurations (QQ q q ) tend to be lower than the threshold 2Q q if the mass ratio is large enough [7]. This is the same favorable breaking of symmetry which makes the hydrogen molecule much more stable than the positronium molecule, in the case where the potential is taken as the Coulomb interaction (see, e.g., [8] for references). Now, the determ...

We calculate the hypertriton binding energy and the d and d scattering lengths using baryon-baryon interactions obtained from a chiral constituent quark model. We study consistently the N N and NN systems by analyzing the effect of the ↔ conversion. Our interactions correctly predict the hypertriton binding energy. The (I, J ) = (0, 3/2) N N channel is also attractive and it might have a bound state. From the condition of nonexistence of a (0,3/2) N N bound state, an upper limit for the spin-triplet N scattering length is obtained. We also present results for the elastic and inelastic N and N cross sections. The consistent description of the N scattering cross sections imposes a lower limit for the corresponding spin-triplet scattering lengths. In the NN system the only attractive channels are (I, J ) = (1, 1/2) and (0, 1/2), the (1, 1/2) state being the most attractive one.

We present an exact calculation of S and P wave QQnn states using different standard nonrelativistic quark-quark potentials. We explore in detail the charm and bottom sectors looking for bound states that could be measured within existing facilities. Against the proliferation of four-quark states sometimes predicted in the literature, we found a small number of candidates to be stable. We analyze their properties in a trial to distinguish between compact and molecular states. Possible decay modes are discussed.