2,566 research outputs found
Meson-baryon interaction in the meson exchange picture
This is the contribution to the proceedings of the MENU 2010 conference. The
recent work of Ref. [7] is summarized. Elastic piN scattering and the reaction
pi^+ p --> K^+ Sigma^+ are described simultaneously in a unitary
coupled-channels approach which respects analyticity. SU(3) flavor symmetry is
used to relate the t- and 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. The
pole structure of the amplitudes is extracted from the analytic continuation.Comment: 4 pages, contribution to the proceedings of the MENU 2010 conference,
May 31- June 4, 2010, Williamsburg VA, US
Three-body Unitarity in the Finite Volume
The physical interpretation of lattice QCD simulations, performed in a small
volume, requires an extrapolation to the infinite volume. A method is proposed
to perform such an extrapolation for three interacting particles at energies
above threshold. For this, a recently formulated relativistic
amplitude based on the isobar formulation is adapted to the finite volume. The
guiding principle is two- and three-body unitarity that imposes the imaginary
parts of the amplitude in the infinite volume. In turn, these imaginary parts
dictate the leading power-law finite-volume effects. It is demonstrated that
finite-volume poles arising from the singular interaction, from the external
two-body sub-amplitudes, and from the disconnected topology cancel exactly
leaving only the genuine three-body eigenvalues. The corresponding quantization
condition is derived for the case of three identical scalar-isoscalar particles
and its numerical implementation is demonstrated.Comment: 9 pages, 3 figure
The impact of photoproduction on the resonance spectrum
The J\"ulich-Bonn coupled-channel framework is extended to
photoproduction. The spectrum of nucleon and resonances is extracted
from simultaneous fits to several pion-induced reactions in addition to pion,
eta and photoproduction off the proton. More than 40,000 data
points up to a center-of-mass energy of E2.3 GeV including recently
measured double-polarization observables are analyzed. The influence of the
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.
Correlations of Partial Waves for Multi-Reaction Analyses
In the search for missing baryonic resonances, many analyses include data
from a variety of pion- and photon-induced reactions. For elastic
scattering, however, usually the partial waves of the SAID or other groups are
fitted, instead of data. We provide the partial-wave covariance matrices needed
to perform correlated fits, in which the obtained equals the
actual up non-linear and normalization corrections. For any analysis
relying on partial waves extracted from elastic pion scattering, this is a
prerequisite to assess the significance of resonance signals and to assign any
uncertainty on results. The influence of systematic errors is also considered.Comment: 7 pages, 3 figures; Acknowledgements update
Charge fluctuations and electric mass in a hot meson gas
Net-Charge fluctuations in a hadron gas are studied using an effective
hadronic interaction. The emphasis of this work is to investigate the
corrections of hadronic interactions to the charge fluctuations of a
non-interacting resonance gas. Several methods, such as loop, density and
virial expansions are employed. The calculations are also extended to SU(3) and
some resummation schemes are considered. Although the various corrections are
sizable individually, they cancel to a large extent. As a consequence we find
that charge fluctuations are rather well described by the free resonance gas.Comment: 32 pages, 18 figure
Developing modern multifunctional agroforestry systems for sustainable intensification
Agroforestry is a land-use system that integrates trees and shrubs with crops and/or livestock production. It has been identified by the International Assessment of Agricultural Knowledge, Science and Technology for Development (IAASTD, 2008) as a ‘win-win’ approach that balances the production of commodities (food, feed, fuel, fibre, etc.) with non-commodity outputs such as environmental protection and cultural and landscape amenities. This paper will review the potential of agroforestry as part of a multifunctional working landscape in temperate regions, and will consider management and policy implications of widespread adoption of this form of land-use
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
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
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