Theoretical studies in hadronic and nuclear physics. Progress report, December 1, 1992--June 30 , 1993

Abstract

Research in the Maryland Nuclear Theory Group focusses on problems in four basic areas of current relevance. The section on Hadrons in Nuclei reports research into the ways in which the properties of nucleons and the mesons which play a role in the nuclear force are modified in the nuclear medium. QCD sum rules supply a new insight into the decrease of the nucleon`s mass in the nuclear medium. The quark condensate decreases in nuclear matter, and this is responsible for the decrease of the nucleon`s mass. The section on the Structure of Hadrons reports progress in understanding the structure of the nucleon. These results cover widely different approaches -- lattice gauge calculations, QCD sum rules, quark-meson models with confinement and other hedgehog models. Progress in Relativistic Nuclear Physics is reported on electromagnetic interactions in a relativistic bound state formalism, with applications to elastic electron scattering by deuterium, and on application of a two-body quasipotential equation to calculate the spectrum of mesons formed as bound states of a quark and antiquark. A Lorentz-invariant description of the nuclear force suggests a decrease of the nucleon`s mass in the nuclear medium similar to that found from QCD sum rules. Calculations of three-bodymore » bound states with simple forms of relativistic dynamics are also discussed. The section on Heavy Ion Dynamics and Related Processes describes progress on the (e{sup +}e{sup {minus}}) problem and heavy-on dynamics. In particular, the sharp electrons observed in {beta}{sup +} irradiation of heavy atoms have recently been subsumed into the ``Composite Particle Scenario,`` generalizing the ``(e{sup +}e{sup {minus}}-Puzzle`` of the pairs from heavy ion collisions to the ``Sharp Lepton Problem.``« less