Baryon resonances and strong QCD

Light-baryon resonances (with u,d, and s quarks in the SU(3) classification) fall on Regge trajectories. When their squared masses are plotted against the intrinsic orbital angular momenta {\rm L}, $\Delta^*$'s with even and odd parity can be described by the same Regge trajectory. For a given {\rm L}, nucleon resonances with spin {\rm S}=3/2 are approximately degenerate in mass with $\Delta$ resonances. To which total angular momentum {\rm L} and {\rm S} couple has no significant impact on the baryon mass. Nucleons with spin 1/2 are shifted in mass; the shift is - in units of squared masses - proportional to the component in the wave function which is antisymmetric in spin and flavor. Based on these observations, a new baryon mass formula is proposed which reproduces nearly all known baryon masses. It is shown that the masses are compatible with a quark-diquark picture while the richness of the experimentally known states require three particles to participate in the dynamics. This conflict is resolved by proposing that quarks polarize the QCD condensates and are surrounded by a polarization cloud shielding the color. A new interpretation of constituent quarks as colored quark clusters emerges; their interaction is responsible for the mass spectrum. Fast flavor exchange between the colored quark clusters exhausts the dynamical richness of the three-particle dynamics. The colored-quark-cluster model provides a mechanism in which the linear confinement potential can be traced to the increase of the volume in which the condensates are polarized. The quark-spin magnetic moment induces currents in the polarized condensates which absorb the quark-spin angular momentum: the proton spin is not carried by quark spins. The model provides a new picture of hybrids and glueballs.Comment: 33 pages, 8 Figure

SU(3) SU(3) Classification of p p -Wave ηπ \eta\pi and η′π \eta'\pi Systems

An exotic meson, the $\pi_1(1400)$ with $J^{PC}=1^{-+}$, has been seen to decay into a p-wave $\eta\pi$ system. If this decay conserves flavor SU(3), then it can be shown that this exotic meson must be a four-quark state ($q\bar q+q\bar q$) belonging to a flavor ${\bf10}\oplus{\bf\bar{10}}$ representation of SU(3). In contrast, the $\pi_1(1600)$ with a substantial decay mode into $\eta'\pi$ is likely to be a member of a flavor octet.Comment: 8 page

Do parity doublets in the baryon spectrum reflect restoration of chiral symmetry?

We discuss the mass spectrum of highly-excited nucleon and $\Delta^*$ resonances. The spectrum exhibits parity doublets, pairs of resonances of identical total angular momentum J but of opposite parity. It has been proposed that the parity doublets evidence restoration of chiral symmetry at large baryon excitation energies. We compare this conjecture with the possibility that high-mass states are organized into $(L,S)$-multiplets with defined intrinsic quark spins and orbital angular momenta. Indeed, the latter interpretation results in a better description of the data. There is however a small and statisticially not very significant trend of the data which might indicate that chiral symmetry is not yet restored but does influence the masses of highly excited states.Comment: 10 pages, 1 fi

Baryon-baryon and baryon-antibaryon interaction amplitudes in the spin--momentum operator expansion method

Partial wave scattering amplitudes in baryon-baryon and baryon-antibaryon collisions and amplitudes for the production and decay of baryon resonances are constructed in the framework of the spin-momentum operator expansion method. The approach is relativistically invariant and it allows us to perform combined analyses of different reactions imposing analyticity and unitarity directly. The role of final state interactions (triangle and box diagrams) is discussed.Comment: 23 pages, 10 figure

Vector mesons in qqˉqˉq\bar q\bar q systems

A new selection rule is described for the vector mesons in the decuplet representations of flavor SU(3)Comment: 7 pages and 1 figur

Light Hadron Spectroscopy: Theory and Experiment

Rapporteur talk at the Lepton-Photon Conference, Rome, July 2001: reviewing the evidence and strategies for understanding scalar mesons, glueballs and hybrids, the gluonic Pomeron and the interplay of heavy flavours and light hadron dynamics. Dedicated to the memory of Nathan Isgur, long-time collaborator and friend, whose original ideas in hadron spectroscopy formed the basis for much of the talk.Comment: to be published in "Lepton Photon 2001 Conference Proceedings" (World Scientific Publishing), 19 pages with 6 figure

Large-scale albuminuria screen for nephropathy models in chemically induced mouse mutants

Background/Aim: Phenotype-driven screening of a great pool of randomly mutant mice and subsequent selection of animals showing symptoms equivalent to human kidney diseases may result in the generation of novel suitable models for the study of the pathomechanisms and the identification of genes involved in kidney dysfunction. Methods: We carried out a large-scale analysis of ethylnitrosourea (ENU)-induced mouse mutants for albuminuria by using qualitative SDS-polyacrylamide gel electrophoresis. Results: The primary albuminuria screen preceded the comprehensive phenotypic mutation analysis in a part of the mice of the Munich ENU project to avoid loss of mutant animals as a consequence of prolonged suffering from severe nephropathy. The primary screen detected six confirmed phenotypic variants in 2,011 G1 animals screened for dominant mutations and no variant in 48 G3 pedigrees screened for recessive mutations. Further breeding experiments resulted in two lines showing a low phenotypic penetrance of albuminuria. The secondary albuminuria screen was carried out in mutant lines which were established in the Munich ENU project without preceding primary albuminuria analysis. Two lines showing increased plasma urea levels were chosen to clarify if severe kidney lesions are involved in the abnormal phenotype. This analysis revealed severe albuminuria in mice which are affected by a recessive mutation leading to increased plasma urea and cholesterol levels. Conclusion: Thus, the phenotypic selection of ENU-induced mutants according to the parameter proteinuria in principle demonstrates the feasibility to identify nephropathy phenotypes in ENU-mutagenized mice. Copyright (C) 2005 S. Karger AG, Basel

Photoproduction of η\eta mesons off neutrons from a deuteron target

A formalism is developed for the partial wave analysis of data on meson photoproduction off deuterons and applied to photoproduction of $\eta$ and $\pi^0$ mesons. Different interpretations of a dip-bump structure of the $\eta$ photoproduction cross section in the 1670 MeV region are presented and discussed. Helicity amplitudes for two low-mass $S_{11}$ states are determined.Comment: 11 pages, 13 figure