# Theoretical Medium Energy Particle Physics

Faculty: |
Leonard Kisslinger Colin Morningstar |

## Group Overview

Theoretical medium energy particle physics (or nuclear physics) centers on the study of the strong and weak nuclear forces. Topics include properties of nuclei, formation of hadrons (such as protons and neutrons) out of quarks and gluons, confinement of quarks, exotic forms of matter involving excitations of gluons, and astrophysical applications, such as neutron stars, supernovae, and phase transitions in the early universe. Theoretical techniques range from pencil-and-paper quantum mechanics to intensive Markov-chain Monte Carlo path integrations on massively parallel supercomputers. We frequently interact with the medium energy experimental groups and high energy theorists in our department and at the University of Pittsburgh. We have ongoing collaborations with theorists at other universities in the US and abroad.

## Member Research Thrusts

**Morningstar** uses Markov-chain Monte Carlo computations in quantum chromodynamics (QCD) with a space-time lattice regulator to investigate hadron formation and quark confinement. He has computed the mass spectrum of glueballs in the Yang-Mills theory of gluons, studied the excitation spectrum of the effective QCD string between a static quark-antiquark pair, and obtained the first glimpse of the nucleon excitation mass spectrum from QCD. He is a member of a large nationwide collaboration of lattice QCD theorists dedicated to Monte Carlo calculations of QCD observables on large-scale computing clusters. He and Curtis Meyer built and maintain the CMU QCD cluster.

**Kisslinger** uses a variety of techniques, such as QCD sum rules, Dyson-Schwinger equations, and light-front field theory, to study QCD and electroweak processes for deducing the structure of hadrons and nuclei, early universe phase transitions, cosmic electroweak bubbles, and pulsar kicks.