Pion photoproduction in a dynamical coupled-channel model

Pion photoproduction reactions are investigated in a dynamical coupled-channel approach based on the Juelich pi-N model, which presently includes the hadronic pi-N and eta-N stable channels as well as the pi-Delta, sigma-N and rho-N effective channels. This model has been quite successful in the description of pi-N to pi-N scattering for center-of-mass energies up to 1.9 GeV. The full pion photoproduction amplitude is constructed to satisfy the generalized Ward-Takahashi identity and hence, it is fully gauge invariant. The calculated differential cross sections and photon spin asymmetries up to 1.65 GeV center-of-mass energy for the reactions gamma p to pi+ n, gamma p to pi0 p and gamma n to pi- p are in good agreement with the experimental data.Comment: Invited talk given at 12th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU2010), Williamsburg, USA, May 31-June 4 201

Divided Government European Style? Electoral and Mechanical Causes of European Parliament and Council Divisions

Voters who participate in elections to the European Parliament tend to use these elections to punish their domestic governing parties. Many students of the EU therefore claim that the party-political composition of the Parliament should systematically differ from that of the Council. This study, which compares empirically the party-political centers of gravity of these two central political actors, shows that opposed majorities between Council and Parliament may have other than simply electoral causes. The logic of domestic government formation works against the representation of politically more extreme parties, and hence against more EU-skeptic parties in the Council. At the same time, voters in EP elections vote more often for these more extreme and more EU-skeptic parties. The different locations of Council and Parliament in the pro-/contra-EU dimension may thus be caused by two – possibly interrelated – effects: a mechanical effect, due to the translation of votes into seats and then into 'office', and thus also into Council representation, and an electoral effect in elections to the European Parliament. The paper discusses the implications of this finding for our understanding of the political system of the EU and of its democratic legitimacy.Regelmäßig scheinen Wähler Europawahlen dazu zu nutzen, ihre jeweilige nationale Regierung elektoral zu bestrafen. Viele Beobachter der Wahlen zum Europäischen Parlament gehen daher davon aus, dass die parteipolitische Ausrichtung des Parlaments systematisch von der des Ministerrats abweicht. Die vorliegende Analyse, die die parteipolitische Zusammensetzung dieser beiden zentralen europapolitischen Akteure empirisch vergleicht, zeigt, dass neben den elektoralen Ursachen auch andere Gründe für gegenläufige Mehrheiten zwischen Parlament und Rat verantwortlich sein können. Die Logik der Regierungsbildung auf nationalstaatlicher Ebene führt dazu, dass "zentristische" und damit eher europafreundliche Parteien überproportional stark im Rat vertreten sind. In Europawahlen hingegen geben Wähler häufig extremer positionierten, das heißt auch europaskeptischeren Parteien ihre Stimme. Die politische Distanz zwischen Rat und Parlament resultiert in der Pro/contra-EU-Dimension daher aus dem Zusammenwirken zweier, möglicherweise miteinander verbundener Effekte: elektoralen und "mechanischen" Gründen für divided government in Europa. Das Papier diskutiert die Implikationen dieses Befundes für unser Verständnis von der Funktionsweise der EU und ihrer demokratischen Legitimation

Aspekte des Pflanzenschutzes bei der Pflanzgutvorbereitung von ökologisch produzierten Kartoffeln

Presprouting of seed tubers is a measure that is often recommended for organic potato growing. In on-farm field experiments the effect of presprouting was evaluated with respect to virus infection, yield and weed infestation. The effect of presprouting on yield was largely dependent on the year and on the late blight severity. Weeds were not affected significantly by presprouting. In most experiments virus incidence was higher in presprouted potatoes. Presprouting also had a suppressive effect on undesired regrowth after haulm destruction

Dynamical coupled-channel approaches on a momentum lattice

Dynamical coupled-channel approaches are a widely used tool in hadronic physics that allow to analyze different reactions and partial waves in a consistent way. In such approaches the basic interactions are derived within an effective Lagrangian framework and the resulting pseudo-potentials are then unitarized in a coupled-channel scattering equation. We propose a scheme that allows for a solution of the arising integral equation in discretized momentum space for periodic as well as twisted boundary conditions. This permits to study finite size effects as they appear in lattice QCD simulations. The new formalism, at this stage with a restriction to S-waves, is applied to coupled-channel models for the sigma(600), f0(980), and a0(980) mesons, and also for the Lambda(1405) baryon. Lattice spectra are predicted.Comment: 7 pages, 4 figure

Dynamical coupled-channels model study of pion photoproduction

The photoproduction of pion off nucleon is investigated within a dynamical coupled-channels approach based on the Juelich pi-N model, which has been quite successful in the description of pi-N to pi-N scattering for center-of-mass energies up to 1.9 GeV. The full pion photoproduction amplitude is constructed to satisfy the generalized Ward-Takahashi identity and hence, it is fully gauge invariant. The calculated differential cross sections and photon spin asymmetries up to 1.65 GeV center-of-mass energy for the reactions gamma p to pi^+ n, gamma p to pi^0 p and gamma n to pi^- p are in good agreement with the experimental data.Comment: Talk given at The 8th International Workshop on the Physics of Excited Nucleons (NSTAR2011), May 17-20, 2011, Thomas Jefferson National Accelerator Facility, Newport News, Virginia, US

Photocouplings at the Pole from Pion Photoproduction

The reactions $\gamma p\to\pi^0 p$ and $\gamma p\to\pi^+ n$ are analyzed in a semi-phenomenological approach up to $E\sim2.3$ GeV. Fits to differential cross section and single and double polarization observables are performed. A good overall reproduction of the available photoproduction data is achieved. The J\"ulich2012 dynamical coupled-channel model -which describes elastic $\pi N$ scattering and the world data base of the reactions $\pi N\to\eta N$, $K\Lambda$, and $K\Sigma$ at the same time - is employed as the hadronic interaction in the final state. The framework guarantees analyticity and, thus, allows for a reliable extraction of resonance parameters in terms of poles and residues. In particular, the photocouplings at the pole can be extracted and are presented.Comment: 37 pages, 31 figures. Angles of the photocouplings at the pole adapted to the convention of Phys. Rev. C 87, 068201 (2013

Coupled-channel dynamics in the reactions piN --> piN, etaN, KLambda, KSigma

Elastic piN scattering and the world data of the family of reactions pi^- p --> eta n, K^0 Lambda$, K^0 Sigma^0, K^+ Sigma^-, and pi^+ p --> K^+ Sigma^+ are described simultaneously in an analytic, unitary, coupled-channel approach. SU(3) flavor symmetry is used to relate both the t- and the u- channel exchanges that drive the meson-baryon interaction in the different channels. Angular distributions, polarizations, and spin-rotation parameters are compared with available experimental data. Partial-wave amplitudes are determined and the resonance content is extracted from the analytic continuation, including resonance positions and branching ratios, and possible sources of uncertainties are discussed. The results provide the final-state interactions for the ongoing analysis of photo- and electroproduction data.Comment: 53 pages, 48 figures; results updated to published versio

Scalar mesons moving in a finite volume and the role of partial wave mixing

Phase shifts and resonance parameters can be obtained from finite-volume lattice spectra for interacting pairs of particles, moving with nonzero total momentum. We present a simple derivation of the method that is subsequently applied to obtain the pi pi and pi K phase shifts in the sectors with total isospin I=0 and I=1/2, respectively. Considering different total momenta, one obtains extra data points for a given volume that allow for a very efficient extraction of the resonance parameters in the infinite-volume limit. Corrections due to the mixing of partial waves are provided. We expect that our results will help to optimize the strategies in lattice simulations, which aim at an accurate determination of the scattering and resonance properties.Comment: 19 pages, 12 figure