Baryon Spectroscopy and the Origin of Mass

The proton mass arises from spontaneous breaking of chiral symmetry and the formation of constituent quarks. Their dynamics cannot be tested by proton tomography but only by studying excited baryons. However, the number of excited baryons is much smaller than expected within quark models; even worse, the existence of many known states has been challenged in a recent analysis which includes - compared to older analyses - high-precision data from meson factories. Hence $\pi N$ elastic scattering data do not provide a well-founded starting point of any phenomenological analysis of the baryon excitation spectrum. Photoproduction experiments now start to fill in this hole. Often, they confirm the old findings and even suggest a few new states. These results encourage attempts to compare the pattern of observed baryon resonances with predictions from quark models, from models generating baryons dynamically from meson-nucleon scattering amplitudes, from models based on gravitational theories, and with the conjecture that chiral symmetry may be restored at high excitation energies. Best agreement is found with a simple mass formula derived within AdS/QCD. Consequences for our understanding of QCD are discussed as well as experiments which may help to decide on the validity of models.Comment: Hadron 2009 invited talk, 8 pages, 6 figures, 4 table

Nucleon Excitations

The mass pattern of nucleon and $\Delta$ resonances is compared with predictions based on quark models, the Skyrme model, AdS/QCD, and the conjecture of chiral symmetry restoration.Comment: QNP-2009, Beijing, invited tal

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

Committing to Incentives: Should the Decision to Sanction be Revealed or Hidden?

Sanctions are widely used to promote compliance in principal-agent-relationships. While there is ample evidence confirming the predicted positive incentive effect of sanctions, it has also been shown that imposing sanctions may in fact reduce compliance by crowding-out intrinsic motivation. We add to the literature on the hidden costs of control by showing that these costs are restricted to situations where principals ex ante reveal their decision to sanction low compliance. If this decision is not revealed and agents do not know whether they will be sanctioned or not in case of low compliance, we do not find evidence of crowding-out - not even in those cases where agents firmly believe that they will be sanctioned in case of low performance.Intrinsic Motivation, Monetary Incentives, Job Performance

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

Committing to incentives: Should the decision to sanction be revealed or hidden?

Sanctions are widely used to promote compliance in principal-agent-relationships. While there is ample evidence confirming the predicted positive incentive effect of sanctions, it has also been shown that imposing sanctions may in fact reduce compliance by crowding-out intrinsic motivation. We add to the literature on the hidden costs of control by showing that these costs are restricted to situations where principals ex ante reveal their decision to sanction low compliance. If this decision is not revealed and agents do not know whether they will be sanctioned or not in case of low compliance, we do not find evidence of crowding-out - not even in those cases where agents firmly believe that they will be sanctioned in case of low performance

Praktikabilität des Kontrollverfahrens zum GVO-Verbot im Ökologischen Landbau

Ziel des im Rahmen des BÖL geförderten Projektes war die Weiterentwicklung des Kontrollverfahrens nach VO (EWG) Nr. 2092/91 (EG-Öko-VO) hinsichtlich der Überprüfung des Einsatzverbotes genetisch veränderter Organismen (GVO) und deren Derivate bei ökologisch erzeugten Produkten. Es wurde als Kooperation zwischen dem Bundesinstitut für Risikobewertung (BfR) und der Kontrollstelle Gesellschaft für Ressourcenschutz mbH (GfRS) durchgeführt. Methodische Grundlagen des Kontrollverfahrens wurden analysiert, wobei die Schnittstellen zwischen ökologischer und konventioneller Produktion von besonderem Interesse waren. Als Ergebnis wird eine Kontrollsystematik vorgeschlagen, mit der Kontrollstellen die Einhaltung des GVO-Verbotes überprüfen können. Die Komponenten dieser Kontrollsystematik enthalten eine Interpretation des Anwendungsverbotes von GVO und GVO-Derivaten. Eine Risikoliste enthält Stoffe aus der konventionellen Produktion, die nach EG-Öko-VO wirtschaftende Betriebe einsetzen dürfen und die GVO und/oder GVO-Derivate enthalten oder sein könnten. Bei risikoorientierten Betriebsbegehungen wurden kritische Kontrollpunkte in Erzeugungs-, Verarbeitungs- und Importunternehmen von Lebens- und Futtermitteln identifiziert. Die Kontrollsystematik wurde in einer Musterverfahrensanweisung formuliert. Diese wurde durch eine erweiterte Risikoliste, Listen kritischer Kontrollpunkte für vier Unternehmenstypen, eine Übersicht wichtiger Probenahmevorschriften, Probenahmeformulare und eine Checkliste für Inspektionsbesuche ergänzt. Innerhalb des Projektes wurden 65 Produkte (Lebensmittel, Futtermittel, Saatgut) mittels Real-Time PCR auf die Anwesenheit von GVO untersucht. Die quantitativen Analysen ergaben bei konventionellen Futtermitteln Hinweise auf den Einsatz von GVO. Die in ökologisch erzeugten Futtermitteln ermittelten GVO-Anteile waren geringer und deuteten eher auf eine Verunreinigung hin. Ein Nachweis von gentechnisch veränderten Mikroorganismen, zur Frage ob es sich bei einem Stoff um ein GVO-Derivat handelt oder nicht, sollte nicht über ein molekularbiologisches Verfahren durchgeführt werden. Die Ergebnisse des Projektes werden in Form eines Handbuches für die Anwendungspraxis verfügbar gemacht