Finite volume effects and quark mass dependence of the N(1535) and N(1650)

For resonances decaying in a finite volume, the simple identification of state and eigenvalue is lost. The extraction of the scattering amplitude is a major challenge as we demonstrate by extrapolating the physical S_{11} amplitude of pion-nucleon scattering to the finite volume and unphysical quark masses, using a unitarized chiral framework including all next-to-leading order contact terms. We show that the pole movement of the resonances N(1535)1/2^- and N(1650)1/2^- with varying quark masses is non-trivial. In addition, there are several strongly coupled S-wave thresholds that induce a similar avoided level crossing as narrow resonances. The level spectrum is predicted for two typical lattice setups, and ways to extract the amplitude from upcoming lattice data are discussed.Comment: 8 pages, 5 .eps figure

The impact of K+Λ\mathbf{K^+\Lambda} photoproduction on the resonance spectrum

The J\"ulich-Bonn coupled-channel framework is extended to $K^+\Lambda$ photoproduction. The spectrum of nucleon and $\Delta$ resonances is extracted from simultaneous fits to several pion-induced reactions in addition to pion, eta and $K^+\Lambda$ photoproduction off the proton. More than 40,000 data points up to a center-of-mass energy of E$\sim$2.3 GeV including recently measured double-polarization observables are analyzed. The influence of the $\gamma p\to K^+\Lambda$ channel on the extracted resonance parameters and the appearance of states not seen in other channels is investigated. The J\"ulich-Bonn model includes effective three-body channels and guarantees unitarity and analyticity, which is a prerequisite for a reliable determination of the resonance spectrum in terms of poles and residues.Comment: 21 pages, 11 figures. Minor modifications, additional information in the appendix. Accepted for publication in Eur. Phys. J.

Biotic indicators of carabid species richness on organically and conventionally managed arable fields

Carabids, a species rich arthropod family, potentially contribute much to biodiversity in agroecosystems, but assessing and monitoring carabid diversity is costly and time consuming. Therefore, this study aimed at finding more easily measurable parameters indicating high carabid diversity within organic and conventional management systems. Cover and number of weed species as well as activity density of single carabid species and of total carabids were investigated as potential indicators of carabid species richness. The study was carried out near Reckenfeld in Westphalia on sandy Plaggenesch soils. Three organically and four conventionally managed fields (cereals and corn) were investigated at the field margins and in the field centres from April to August 1999. Additionally, data of carabid catches and weed flora in winter cereals from an extended study in Düren (Northrhine-Westphalia) were reanalysed to validate the results. However, neither of the potential indicators showed consistently significant positive correlation with carabid diversity. This is partly attributed to the low variability of management conditions within the management systems in the studies presented

Finite volume effects in pion-kaon scattering and reconstruction of the kappa(800) resonance

Simulating the kappa(800) on the lattice is a challenging task that starts to become feasible due to the rapid progress in recent-years lattice QCD calculations. As the resonance is broad, special attention to finite-volume effects has to be paid, because no sharp resonance signal as from avoided level crossing can be expected. In the present article, we investigate the finite volume effects in the framework of unitarized chiral perturbation theory using next-to-leading order terms. After a fit to meson-meson partial wave data, lattice levels for piK scattering are predicted. In addition, levels are shown for the quantum numbers in which the sigma(600), f_0(980), a_0(980), phi(1020), K*(892), and rho(770) appear, as well as the repulsive channels. Methods to extract the kappa(800) signal from the lattice spectrum are presented. Using pseudo-data, we estimate the precision that lattice data should have to allow for a clear-cut extraction of this resonance. To put the results into context, in particular the required high precision on the lattice data, the sigma(600), the P-wave resonances K*(892) and rho(770), and the repulsive piK, pipi phases are analyzed as well.Comment: 31 pages, 14 figure

Hochvernetzte Poyethylene in der Hüftendoprothetik

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Die Notwendigkeit künstlicher Hüftgelenke nimmt mit dem steigenden Durchschnittsalter der Bevölkerung zu. Etwa 0,1% der Bevölkerung der Welt mit „westlicher" Lebensweise benötigt ein künstliches Hüftgelenk. Die derzeit verwendeten Werkstoffe in der Hüftendoprothetik besitzen, trotz stetiger Verbesserungen, immer noch zu hohe Abriebswerte. Somit ist das Hauptziel der heutigen Forschung über Werkstoffe für die Endoprothetik, Reibungsparmer zu finden, die über einen langfristigen Zeitraum weniger Verschleiß aufweisen, bei gleichzeitiger Biokompatibilität. Derzeit ist häufig von XPE (hochvernetztes UHMW-PE) die Rede. Die sehr guten Abriebswerte von XPE geben Anlaß zu Hoffnung, ein geeignetes Material gefunden zu haben. Aber wie sieht es mit den anderen Eigenschaften aus? Unterschiedlichste Herstellungs- und Prüfmethoden erschweren den direkten Vergleich der Eigenschaften. XPE kann entweder durch Bestrahlung von UHMW-PE hergestellt werden, oder durch chemische Reaktionen mittels organischen Peroxiden. Bei der Bestrahlung können entweder Gammastrahlen oder Elektronenstrahlen zum Einsatz kommen. Die chemische Herstellung spielt im Moment noch keine große Rolle und wird deshalb im Folgenden nicht näher behandelt. In dieser Arbeit wurde versucht, aus bereits unternommenen Studien Tendenzen ableiten zu können, ob XPE den Erwartungen entspricht

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

Topos quantum theory with short posets

Topos quantum mechanics, developed by Isham et. al., creates a topos of presheaves over the poset V(N) of abelian von Neumann subalgebras of the von Neumann algebra N of bounded operators associated to a physical system, and established several results, including: (a) a connection between the Kochen-Specker theorem and the non-existence of a global section of the spectral presheaf; (b) a version of the spectral theorem for self-adjoint operators; (c) a connection between states of N and measures on the spectral presheaf; and (d) a model of dynamics in terms of V(N). We consider a modification to this approach using not the whole of the poset V(N), but only its elements of height at most two. This produces a different topos with different internal logic. However, the core results (a)--(d) established using the full poset V(N) are also established for the topos over the smaller poset, and some aspects simplify considerably. Additionally, this smaller poset has appealing aspects reminiscent of projective geometry.Comment: 14 page

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

Thermal fluctuation field for current-induced domain wall motion

Current-induced domain wall motion in magnetic nanowires is affected by thermal fluctuation. In order to account for this effect, the Landau-Lifshitz-Gilbert equation includes a thermal fluctuation field and literature often utilizes the fluctuation-dissipation theorem to characterize statistical properties of the thermal fluctuation field. However, the theorem is not applicable to the system under finite current since it is not in equilibrium. To examine the effect of finite current on the thermal fluctuation, we adopt the influence functional formalism developed by Feynman and Vernon, which is known to be a useful tool to analyze effects of dissipation and thermal fluctuation. For this purpose, we construct a quantum mechanical effective Hamiltonian describing current-induced domain wall motion by generalizing the Caldeira-Leggett description of quantum dissipation. We find that even for the current-induced domain wall motion, the statistical properties of the thermal noise is still described by the fluctuation-dissipation theorem if the current density is sufficiently lower than the intrinsic critical current density and thus the domain wall tilting angle is sufficiently lower than pi/4. The relation between our result and a recent result, which also addresses the thermal fluctuation, is discussed. We also find interesting physical meanings of the Gilbert damping alpha and the nonadiabaticy parameter beta; while alpha characterizes the coupling strength between the magnetization dynamics (the domain wall motion in this paper) and the thermal reservoir (or environment), beta characterizes the coupling strength between the spin current and the thermal reservoir.Comment: 16 page, no figur