[en] We show that it is in principle possible to determine the quark-quark potential, in the nonrelativistic potential model, from the baryon spectrum. The method we propose is based on the fact that the lowest order of the hyperspherical-harmonic expansion method, the hypercentral approximation, is an excellent approximation for confining quark-quark potentials. However, our method applies to all cases where this assumption is valid. Using standard inverse spectrum techniques adapted to our problem we invert the baryon spectrum to obtain the hypercentral potential in the hyperradius of the three-quark system. By means of a new exact relation based on the Abel integral equation, we can invert the hypercentral potential to determine the quark-quark potential. A first application of this new method to the inversion of the s-state baryon spectrum demonstrates in a model-independent way the inability of nonrelativistic two-quark potentials to reproduce the Roper resonance without violating the QCD-motivated concavity requirement. (authors)

[en] Fermi statistics requires that all the quarks in a nucleus be anti-symmetrized, and hence be exchanged in proportion to the degree of nucleon overlap. This has several important implications. First, it leads to a shift in the distribution of quark momentum relative to that in isolated nucleons. Second, it leads to an important contribution to the quark-quark correlation, from which one deduces an effective nucleon size which is an increasing function of nuclear density. In this paper a simple analytic formula for the effective nucleon radius is obtained

[en] The Dyson Schwinger equation for the quark self energy is employed to investigate the singularity structure of the quark propagator. An effective gluon two-point function, which is free of singularities and consistent with the known asymptotic form, is used to represent the quark-quark interaction. The parameters introduced by the gluon two-point function are constrained by pion observables through the equivalence of the Dyson Schwinger and pion Bethe-Salpeter equations for on-shell pions (a result of Goldstone's theorem). With the parameters fixed, the Dyson-Schwinger equation is used to investigate the singularity structure of the quark propagator through continuation into the complex plane. The quark appears as a broad resonance centered at the expected constituent quark mass. Comments are made on the relevance of this result to confinement and the relativistic investigation of meson spectroscopy

[en] Photoexcitation of the nucleon is studied in the framework of the constituent quark model with nonrelativistic quark-quark interactions. Utilizing the dominance of the pairwise structure of the relevant three-quark potential, the bound- and excited-state wave functions have been constructed using the Faddeev-type integro-differential equation approach. The method is based on the hyperspherical harmonics expansion and takes two-body correlations exactly into account and therefore reliable wave functions, required in photo processes, can be obtained. The integrated photoabsorption cross-sections for the E1 and M1 transistors are calculated and compared with experimental values as well as with those of other theoretical calculations. Overall, our results are in good to very good agreement with the experimental values

[en] The authors defend their assertion that the decay rate of a proton in a nucleus may be inhibited compared to that of a free nucleon

[en] A purely left-chiral model of the weak interactions is used to show that the total parity-violating asymmetry in quark-quark scattering must grow with increasing energy. In the absence of other new physics, non-observation of a large asymmetry can therefore be used to infer an upper bound on the mass scale for new right-chiral weak vector bosons. Applying this idea to actual nucleon-nucleon scattering requires more involved calculations, as the dominant contribution appears to come from a component of diquark-quark scattering related to, but not identical to, wavefunction-mixing. Earlier criticism of this model by Simonius and Unger is refuted, and a new calculation is proposed as an additional check on the result. Finally, the author argues that the so-called open-quotes spin crisisclose quotes does not affect the conclusions

[en] We give the results of complete analytical computations of two- and three-point loop integrals occurring in heavy particle theories, with and without velocity change, for arbitrary values of external momenta and masses

No abstract available

[en] The authors explore the diquark-quark picture of the octet and the decuplet low-lying baryons in QCD (quantum chromodynamics) with a linear confinement potential. The mass spectra of scalar, pseudoscalar, vector and axial-vector diquarks are analyzed. For scalar, pseudoscalar and vector diquarks they find bound states with masses M_S≅M_P=1.95 GeV, and M_V=2.40 GeV, whereas for axial-vector diquarks no bound states exist. The low-lying baryons cannot be described by the diquark-quark picture. The results confirm the three-body structure of three-quark currents of low-lying baryons and lead to an unambiguously fixed spinor structure of three-quark currents of low-lying baryons as proposed by Ioffe, Pascual and Tarrach

[en] The possibility of a bound-state effect in the quark-quark interaction is discussed. If such dynamical diquarks exist, they should play a role in the formation and decay of a QCD plasma, as probed in relativistic heavy-ion collisions. In an intermediate temperature range, just above the critical temperature, a diquark plasma component is expected to be important. Quantitative results within a particular model, the Stockholm diquark model, are presented. Possible experimental signatures of such a diquark plasma are suggested