Investigating scalar meson mixing in nucleon--nucleon and deuteron--deuteron collisions

The advantages to study charge--symmetry breaking and especially the phenomenon of f0-a0 mixing in nucleon--nucleon and deuteron--deuteron induced reactions are discussed.Comment: Invited talk at the international High Energy Physics Workshop 'Scalar Mesons: an Interesting Puzzle for QCD', May 16-18, 2003, SUNY Institute of Technology, Utica, New Yor

The piNN system - recent progress

Recent progress towards an understanding of the piNN system within chiral perturbation theory is reported. The focus lies on an effective field theory calculation and its comparison to phenomenological calculations for the reaction NN->d pi. In addition, the resulting absorptive and dispersive corrections to the pi-d scattering length are discussed briefly.Comment: Plenary talk at 5th International Workshop on Chiral Dynamics, theory and Experiment (CD 2006), Durham / Chapel Hill, North Carolina, 18-22 Sep 200

NN-->NNpi from the effective field theory point of view: short comings and gains

Based on a counting scheme for the application of chiral perturbation theory to pion production in NN collisions p-wave production is studied. It is demonstrated that, contrary to the s-wave production where loops enter at too low an order to allow the scheme predictive power, there are certain p-wave observables where parameter free predictions are possible. These predictions are consistent with experimental data. We show that the investigation of charged pion production yields a constraint on a contribution to the three-nucleon force with a spin-isospin structure that could resolve the $A_y$ puzzle in $nd$ scattering.Comment: 4 pages, 3 figures, Contribution to "MESON2000", Workshop on production, properties and interaction of mesons, Cracow, Poland, 19-23 May 200

QCD tests from pion reactions on few-nucleon systems

We show on two examples, namely a calculation for charge symmetry breaking in pn->d pi^0 that allows one to extract the quark mass difference induced part of the proton--neutron mass difference and a high precision calculation for pion--deuteron scattering and its implications for the value of the charged pion--nucleon coupling constant, how QCD tests can be performed from low energy hadronic observables.Comment: 9 pages; Invited talk at workshop CHIRAL'10, Valencia (Spain), June 21-24, 201

Theoretical understanding of pion production in nucleon-nucleon collisions - a status report

A status report is given for the current theoretical understanding of pion production close to threshold. In the first part of the talk predictions of a meson exchange model are compared to recent polarized data for the reactions $pp \to pp\pi^0$ as well as $pp\to pn\pi^+$ revealing, that the former reaction is badly described whereas the predictions for the latter turn out to be consistent with the data. Recent progress in the application of chiral perturbation theory allows to understand this difference.Comment: 3 pages, 1 figure, Presented at the 7th International Workshop on Meson Production, Properties and Interactions, MESON2002, Krakow, Polan

Meson exchange models for Meson production

The production of mesons in nucleon-nucleon collisions is reviewed from the viewpoint of the meson-exchange picture. In the first part various possible production mechanisms and their relative importance are discussed. In addition, general features of meson production are described. In the second part special emphasis is put on pion production. Implications of chiral perturbation theory are discussed. Results based on a specific meson-exchange model for pion production in nucleon-nucleon collisions are presented. The model is utilized to calculate several spin-dependent observables of the reactions $pp \to pp\pi^0$ and $pp \to pn\pi^+$ such as spin-correlation parameters. This allows us to study the role of the Delta resonance at close to threshold energies. The talk closes with a brief discussion of the production of $\phi$ mesons as an example for the production of heavier mesons. A strategy is outlined that allows to extract information on the structure of the nucleon from the reaction $NN \to NN \phi$.Comment: Invited talk at the 4th International Conference on Physics at Storage Rings (STORI99), Bloomington, IN USA, Sept. 12-16, 1999; 15 pages, 6 figure

Modelling low-mass resonances in multi-body decays

Recent advances towards a model-independent description of hadronic few-body final states, relevant for the extraction of direct CP violation from the decays of heavy mesons, are presented.Comment: 10 pages; to appear in the proceedings of The 6th International Workshop on Charm Physics (CHARM 2013

How and when can one identify hadronic molecules in the baryon spectrum

A method to identify hadronic molecules in the particle spectrum is reviewed and the conditions for its applicability discussed. Special emphasis is put on the discussion of molecule candidates in the baryon spectrum.Comment: Talk presentent at NSTAR 2007, 5 - 8 September 2007, Bonn, German

Complete next-to-leading order calculation for pion production in nucleon-nucleon collisions at threshold

Based on a counting scheme that explicitly takes into account the large momentum sqrt(M m_pi) characteristic for pion production in nucleon-nucleon collisions we calculate all diagrams for the reaction NN --> NN pi at threshold up to next-to-leading order. At this order there are no free parameters and the size of the next-to-leading order contributions is in line with the expectation from power counting. The sum of loop corrections at that order vanishes for the process pp --> pp pi^0 at threshold. The total contribution at next-to-leading order from loop diagrams that include the delta degree of freedom vanishes at threshold in both reaction channels pp --> pp pi^0, pn pi^+.Comment: 9 pages, 4 figure