Nucleon matrix elements of the antisymmetric quark tensor

If physics beyond the Standard Model enters well above the electroweak scale, its low-energy effects are described by Standard Model Effective Field Theory. Already at dimension six many operators involve the antisymmetric quark tensor $\bar q \sigma^{\mu\nu} q$, whose matrix elements are difficult to constrain from experiment, Ward identities, or low-energy theorems, in contrast to the corresponding vector and axial-vector or even scalar and pseudoscalar currents. However, with normalizations determined from lattice QCD, analyticity and unitarity often allow one to predict the momentum dependence in a large kinematic range. Starting from recent results in the meson sector, we extend this method to the nucleon case and, in combination with pole dominance, provide a comprehensive assessment of the current status of the nucleon form factors of the quark tensor.Comment: 7 pages, 3 figures; strangeness input update

Extracting the sigma-term from low-energy pion-nucleon scattering

We present an extraction of the pion-nucleon ($\pi N$) scattering lengths from low-energy $\pi N$ scattering, by fitting a representation based on Roy-Steiner equations to the low-energy data base. We show that the resulting values confirm the scattering-length determination from pionic atoms, and discuss the stability of the fit results regarding electromagnetic corrections and experimental normalization uncertainties in detail. Our results provide further evidence for a large $\pi N$ $\sigma$-term, $\sigma_{\pi N}=58(5)$ MeV, in agreement with, albeit less precise than, the determination from pionic atoms.Comment: 17 pages, 3 figures; journal versio

Comparative Analysis of World Market Projections with Special Regard to Wheat Prices

This paper presents a short comparative analysis of USDA and FAPRI projections for world wheat market prices until 2005. The relevance of different model assumptions regarding assumed inflation, exchange rates, policy parameters as well as shifts in demand and production development are discussed. A subsequent section focuses on the problem of a "world market price concept" for evaluating the potential of unsubsidized EU cereal exports. The Annex provides more detailed information on model assumptions and a comparison of other projected values, also including agricultural products other than wheat. Dieses Diskussionspapier stellt eine kurze vergleichende Analyse aktueller USDA- und FAPRI- Projektionen von Weltmarktpreisen fur Weizen bis 2005 vor. Die Relevanz verschiedener Modellannahmen hinsichtlich Inflation, Wechselkurs, Politikparameter und Bestimmungsgrossen von Angebot und Nachfrage werden diskutiert. Einige Uberlegungen zur Problematik eines "Weltmarktpreiskonzeptes" bei der Abschatzung des Potentials unsubventionierter EU Getreideexporte schliessen sich an. Der Anhang stellt detailliertere Informationen zu Modellannahmen sowie den Vergleich weiterer projezierter Kennzahlen bereit, die auch andere Agrarprodukte einschliessen.Demand and Price Analysis,

High-precision determination of the pion-nucleon σ\sigma-term from Roy-Steiner equations

We present a determination of the pion-nucleon ($\pi N$) $\sigma$-term $\sigma_{\pi N}$ based on the Cheng-Dashen low-energy theorem (LET), taking advantage of the recent high-precision data from pionic atoms to pin down the $\pi N$ scattering lengths as well as of constraints from analyticity, unitarity, and crossing symmetry in the form of Roy-Steiner equations to perform the extrapolation to the Cheng-Dashen point in a reliable manner. With isospin-violating corrections included both in the scattering lengths and the LET, we obtain $\sigma_{\pi N}=(59.1\pm 1.9\pm 3.0)$ MeV $=(59.1\pm 3.5)$ MeV, where the first error refers to uncertainties in the $\pi N$ amplitude and the second to the LET. Consequences for the scalar nucleon couplings relevant for the direct detection of dark matter are discussed.Comment: 6 pages, 1 figure; title changed by journal, version to be published in PR

Matching pion-nucleon Roy-Steiner equations to chiral perturbation theory

We match the results for the subthreshold parameters of pion-nucleon scattering obtained from a solution of Roy-Steiner equations to chiral perturbation theory up to next-to-next-to-next-to-leading order, to extract the pertinent low-energy constants including a comprehensive analysis of systematic uncertainties and correlations. We study the convergence of the chiral series by investigating the chiral expansion of threshold parameters up to the same order and discuss the role of the \Delta(1232) resonance in this context. Results for the low-energy constants are also presented in the counting scheme usually applied in chiral nuclear effective field theory, where they serve as crucial input to determine the long-range part of the nucleon-nucleon potential as well as three-nucleon forces.Comment: 6 pages, 4 tables; version to appear in PR

Extracting the sigma-term from low-energy pion-nucleon scattering

We present an extraction of the pion-nucleon ($\pi N$) scattering lengths from low-energy $\pi N$ scattering, by fitting a representation based on Roy-Steiner equations to the low-energy data base. We show that the resulting values confirm the scattering-length determination from pionic atoms, and discuss the stability of the fit results regarding electromagnetic corrections and experimental normalization uncertainties in detail. Our results provide further evidence for a large $\pi N$ $\sigma$-term, $\sigma_{\pi N}=58(5)$ MeV, in agreement with, albeit less precise than, the determination from pionic atoms.Comment: 17 pages, 3 figures; journal versio

Inclusive Jet Cross Sections in pˉp\bar{p}p Collisions at s\sqrt{s}= 630 and 1800 GeV

We have made a precise measurement of the inclusive jet cross section at $\sqrt{s}$=1800 GeV. The result is based on an integrated luminosity of 92 pb^{-1} collected at the Fermilab Tevatron $\bar{p}p$ Collider with the D\O detector. The measurement is reported as a function of jet transverse energy (60 GeV <= E_{T} < 550 GeV), and in the pseudorapidity intervals |\eta| <= 0.5 and 0.1 <= |\eta| <= 0.7. A preliminary measurement of the pseudorapidity dependence of inclusive jet production (|\eta| <= 1.5) is also discussed. The results are in good agreement with predictions from next-to-leading order (NLO) quantum chromodynamics (QCD). D\O has also determined the ratio of jet cross sections at $\sqrt{s}$=630 GeV and $\sqrt{s}$=1800 GeV (|\eta| <= 0.5). This preliminary measurement differs from NLO QCD predictions.Comment: Submitted to the International Europhysics Conference on High Energy Physics, EPS-HEP99, 15-21 July, 1999, Tampere, Finlan