Theory of strangeness dynamics

1. Kaons in nuclear matter: It is the Weinberg-Tomozawa term which is responsible for the different in-medium behavior of kaons and anti-kaons: the effective kaon mass slightly increases with increasing nucleon density, while the effective anti-kaon mass drops significantly. (A review of systematic investigations, including the momentum dependence, can be found in the Ph. D. thesis of E.E. Kolomeitsev size:1.2 Mb.) The experimental findings of the KaoS and FOPI collaborations at GSI Darmstadt seem to confirm these predictions.

In extreme case the anti-kaon mass can drop so much that a Bose condensation happens. A phenomenological implication would be a pronounced softening of the equation of state. As a consequence, neutron stars with a anti-kaon condensate in the core become unstable and collapse towards a black hole. G. Brown and collaboraters have pointed out that an upper bound on neutron star masses can arise from the onset of anti-kaon condensation.

2. K+-, j dynamics in heavy-ion collisions: Relying a on transport model of BUU type the dynamics K+- and j in heavy-ion collsions is studied with the aim to provide a detailed interpretation of the experimental findings. The nucleons experience a momentum dependent interaction, and the pecularities of the K+- potentials and their density dependence are included. The flow pattern of K+ is presently studied and will be extended to a K- in future investigations. The j production is found to proceed mainly via the secondary reactions like pN jN.

3. Elementary phi production processes: The reaction NN NN phi is studied within a one-boson-exchange model. The subprocess N N is properly included. The dominant contribution to the j production stems from the ''radiative conversion'' at the prj vetex , while the direct production in NNj vertices represent minor contributions similar to the ''shake-off'' vertex NNpj. However, it turns out that for several polarization observables that latter two processes are important. In this way a small hidden strangeness fraction in the nucleon becomes experimentally accessible.

for futher information contact B. Kaempfer