# Theory of the strong interactions

IKP-3 / IAS-4

Quantum Chromo Dynamics (QCD) is the theory of the strong interactions. It is a non-abelian gauge theoriy with local SU(3) color symmetry. It's matter fields are the quarks, that appear in six flavors. The interactions are mediated by the spin-1 gauge bosons, the gluons. This interaction is very strong at large distances leading to the phenomenon of color confinement. Thus, quarks and gluons are hidden in hadrons and nuclei. The self-interaction of the gluons and the resulting non-linear dynamics pose one of the grand challenges in contemporary physics. At the IKP, we work on various aspects of QCD in the non-perturbative (strong coupling) regime:

- Structure and dynamics of hadrons based on effective field theories and lattice simulations. Central topics are the calculation of baryon resoances in lattice QCD (in collaboration with the TR 16 at Bonn: Project A.6) and the theory of hadronic molecules, especially in the charm sector.
- Structure and dynamics of atomic nuclei. Based on chiral effective field theory, we construct the forces between nucleons for investigations in few and many-body systems (HUYIG). In particular, we have developed the method of nuclear lattice simulations for ab initio calculations of nuclei and their properties.
- In additon, we perform more phenomenological studies on hadron structure and dynamics for reactions with hadronic and electromagnetic probes as well as for the interaction of charm mesons with matter.

### Medium-term goals and work

The themes of our work are in line with the experimental possibilities at COSY and with experiments on other major equipment of medium energy physics. Priorities are:

- Separation of many particle effects and quark degrees of freedom in nuclear structure and nuclear reactions
- Development and application of theories and models to the non perturbative regime of quantum chromodynamics (QCD)
Description of the structure of hadrons, their quark contents and interaction within the framework of

- effective Meson-Baryon Lagrangians
- effective quark theories
- non linear meson field theories
Emphasis

- a better understanding of the isospin violation in hadronic reactions
- formulation of the connection to chiral perturbation theory with dispersion relations

- Link between meson exchange models and chiral perturbation theory
- Electromagnetic processes at high energy nucleon-nucleon and nucleus-nucleus collisions
- Electromagnetic processes at high energy hadronic reactions
- Modifications of hadrons in nuclei
- High energy electron-nucleon reactions
- Chaos and collectivity in atomic nuclei

### Planned work

- Continuation of the analysis of COSY experiments and the complementary photonuclear experiments at the Mainz Mikrotron (MAMI, Univ. Mainz), at the electron-stretcher accelerator (ELSA, Univ. Bonn) and at Jefferson Lab.
- Meson production at the respective thresholds
- Meson production in the π N-scattering and photonuklearen reactions to the structure of education Nukleonresonanzen
- As part of the Jülich meson exchange model photo production of π, η, η' and the production of η and η' -mesons and the vector mesons ω, φ and 2 pions in proton-proton collisions will be investigated
- The calculation of hadronic form factors in both the space-like as well as the time-like regime within the same model will be continued
- The works in the framework of chiral perturbation theory will concentrate on the use of dispersion relations for the calculation of π N-scattering and the pion-photo production
- Extension to spin-3/2 fileds with application to electroweak form factors and pion production
- In addition the isospin violation in π N-scattering, chiral nucleon-nucleon potentials and the renormalization of effective field theories are investigated
- The application of the coulomb dissociation method to questions of astrophysical nucleon synthesis will be put forward (which is particularly interesting for the new generation of beams of exoitc (radioactive) nuclei (away from the valley of stability))
- The Bremsstrahlung in hadron-hadron collisions at high energy should be further investigated. In the Juelich kaon-nucleon and hyperon-nucleon potential the correlated two-meson exchange will be taken into account. These potentials will the be used in the strangeness production with proton-proton collisions. The self consistent Migdal-theory is numerically implemented and applied to nuclei with large proton or neutron excess
- Investigations of nuclear modifications of the spin-structure functions of the nucleon in the deuteron, and the calculation of tensor polarisation observables in proton-deuteron scattering, which can be studied at COSY
- Full calculation of the quark-distributions in the Reggeon, and the calculation of medium modifications to the valence quark distributions of bound nucleons;
- Investigation of spin-effects in the diffractive production vector mesons and the in-medium modifications of vector mesons, caused by colour-transparency
- Calculation of short-range QCD mechanisms of η' - production at COSY
- Another goal is to calculate the flavor asymmetry in the sea-quark distribution and the strangeness and charm content of the proton