Theoretical Nuclear Physics

Overview

The main emphasis of our group's work now centers around N* physics, driven by the aim of providing a fundamental understanding of the structure of N*s and the dynamics involved in nucleon resonance excitation at relativistic energies. The group also provides theoretical support and guidance to the experimental efforts of GW at JLab and other facilities. We address the issues in a two-pronged approach.

At the hadronic level, the focus is on the interaction and electromagnetic production of the lowest pseudoscalar meson octet (pion, eta, kaon) with the nucleon. Emphasis is placed on a consistent description of hadronic and electromagnetic reactions in a framework that can properly incorporate unitarity, Lorentz covariance and gauge invariance. The goal is to provide a theoretical framework for extracting N* resonance properties as unambiguously as possible. In addition, the group is interested in electromagnetic and weak processes on nuclei and hypernuclei. Current research topics include:

• Coupled-channels Approach to Meson-Nucleon System.
• K-matrix Approach to Meson Photoproduction.
• Analysis of Resonance Multipoles from Polarization Observables in Eta Photoproduction.
• Vector Meson Photoproduction with an Effective Quark Model Lagrangian.
• Effects of Spin 5/2 Resonances in Kaon Photoproduction.

At the quark level, the focus is on understanding hadron structure from QCD (Quantum Chromodynamics, the fundamental theory of the strong interaction). The tools employed are lattice QCD and QCD sum rules. The goal is to provide first-principles calculations for aspects of hadron structure that are of current interest to nuclear physics community, especially those related to the physics program at JLab, using state-of-the-art technology in the field. Current research topics include:

• Hadron magnetic moments, electric and magnetic polarizabilties.
• Excited states of hadrons using overlap quarks and Bayesian priors.
• Exotic states such as tetra- and penta-quarks on the lattice.
• Topological structure of the QCD vacuum.
• High statistics calculation of the E2/M1 and C2/M1 ratios in the N->Delta transitions.
• New and improved QCD sum rules for octect and decuplet baryon masses and magnetic moments.

Faculty

• Cornelius Bennhold
  
• Helmut Haberzettl
• Frank X. Lee
  

Students

• Scott Moerschbacher
• Agung Waluyo
• Ryan Kelly (undergrad, Gamow fellow)
• John Bulava (undergrad)
• Steve Karppi (graduated with PhD August 2004)
• Leming Zhou (graduated with PhD August 2004)
• Xinyu Liu (graduated with PhD November 2003)

Resources

Our research is funded in part by the U.S. Department of Energy under grant DE-FG02-95ER40907. We have access to a variety of computing resources, including

• The 6080-processor Seaborg IBM-SP supercomputer at NERSC (National Energy Research Supercomputing Center), located at Lawrence Livermore National Laboratory, and sponsored by U.S. Department of Energy. This computer is ranked 14th on the world's TOP500 supercomputer list as of June 2004.

• The 3016-processor Lemieux supercomputer at the Pittsburg Supercomputing Center, sponsored by U.S. National Science Foundation. This computer is ranked 25th on the TOP500 list as of June 2004.

• The 1152-processor BlueHorizon at NPACI (National Partnership for Advanced Computing Initiative), located at the San Diego Supercomputing Center, and sponsored by U.S. National Science Foundation.

• The 256-processor Intel Clucter at Jefferson Lab.