Theoretical Nuclear Physics

Carnegie Mellon University, Pittsburgh PA

Investigators

Abstract

Quantum Chromodynamics (QCD) is the theory of strong interactons, with quarks confined by gluonic forces to form protons and other baryons of nuclear physics, as well as quark-antiquark particles, the mesons. It is also possible for the gluons to form particles, called glueballs, without quark constituents. The discovery and study of glueballs is one of the most important areas of nuclear/particle physics. Using QCD, we are investigating possible states of mesons and glueballs with emphasis on identifying experiments to test our theoretical picture. Of particular importance is our recent prediction of a low-mass glueball which we feel is strongly coupled to a two-pion resonance, called the Sigma. We are investigating decay rates of particles which will provide tests of this theory of the glueball/sigma. It is possible to carry out some of these experimental tests at Jefferson Laboratory. We are also carrying out investigations of the Pomeron, whose exchange has long been known to dominate high energy elastic and diffractive processes. It is almost certain that the Pomeron is composed largely of glue, and recently our group has given strong evidence that the Pomeron is closely related to glueballs, including our proposed glueball/sigma. We shall calculate cross sections for sigma production to test the nature of the Pomeron. Experiments could be carried out at the 50 GeV accelerators proposed at Los Alamos Laboratory and in Japan. The proton-proton collider, using the RHIC facility at Brookhaven Laboratory, would be excellent for experimental measurements of the cross sections. Properties of hadrons at finite densities and temperatures are also being investigated. We have completed a preliminary study for hadronic matter at temperatures below the chiral phase transition, which occurs at the temperature of the universe about a millionth of a second after the so-called big bang. We shall study the effect of instantons, certain gluonic modes, on the properties of matter both below and above this phase transition, and propose tests at the RHIC accelarator. We shall also investigate possible evidence for this early-universe phase transition in observational studies of the cosmic microwave background. These interdisciplinary investigations of relationships between nuclear/particle physics and cosmology use field theoretic methods developed in studies of condensed matter physics.