Current Research

My research program is driven by a desire to reveal and understand the long distance properties of the nonperturbative quantum field theory, Quantum Chromodynamics (QCD). QCD describes the interactions of quarks and gluons and the manner in which they form particles such as the proton, neutron, the nucleus, and an extensive list of other particles. The most interesting aspects of the theory lie deep in the nonperturbative long-distance regime where charge radii or magnetic moments probe the theory at scales the size of a proton.

At the CSSM we have a dynamic team of researchers revealing the properties of QCD using fundamental approaches including the first principles method of lattice QCD, currently the most successful, reliable and promising approach to understanding the physical properties of QCD. The model-independent approach of chiral effective field theory complements lattice QCD simulations by providing exact predictions of the nonanalytic behavior of observables in the light quark-mass regime. The numerical simulation of QCD on a space-time lattice complemented by chiral effective field theory provides a fundamental formulation of QCD, ab initio predictions of observables, and the quantitative elimination of systematic errors.

Visualizing the massive amounts of scientific data generated in supercomputer simulations has provided many new insights into the manner in which QCD constructs the world around us.

Research Team Highlights

• Discovered the distribution of quarks within the Λ(1405) via lattice QCD calculations of the electromagnetic form factors.

• Revealed the nature of the famous Λ(1405) state at light quark masses in first-principles 2+1 flavour lattice QCD and showed, for the first time, that the results are consistent with Nature.

• Explored the distributions of quarks within the Roper state and demonstrated a robust link with constituent quark model wave functions.

• Established the essential role of Centre Vortices in the nontrivial vacuum of QCD in underpinning both the confinement of quarks and the dynamical breaking of chiral symmetry, responsible for mass generation in hadronic matter.

• Developed and established an effective correlation-matrix approach to the isolation and extraction of baryon excited states using a novel fermion source and sink smearing approach. This led to the isolation of the otherwise elusive Roper and Λ(1405) baryon resonances in Lattice QCD.

• Created the lattice-QCD based visualizations and animations of QCD vacuum structure and its response to hadrons featured in the 2004 Nobel Prize Acceptance Lecture of Prof. Frank Wilczek, scientific annual reports around the world and in popular international science magazine and newspaper articles.

• Designed and implemented the first comprehensive investigation of spin-0 and spin-1 octet meson electromagnetic form factors in lattice QCD. This work is the first to calculate the quadrupole form factor of the vector meson and reveal that the charge distribution is not spherically symmetric but rather has an oblate shape.

• Developed new methods for identifying the power-counting regime of chiral perturbation theory.

• Created a novel formalism involving (quenched) chiral effective field theory and lattice QCD simulations for determining the strangeness magnetic moment of the nucleon, G_M^s = -0.046 +/- 0.019 μ_N, an order of magnitude more precise than the experimental measurements of 2004.

• Revealed the presence of chiral nonanalytic behavior in the magnetic moments of octet and decuplet baryons via numerical simulations of FLIC fermions in the light quark-mass regime of QCD.

• Established the improved convergence properties of Finite-Range-Regularized (FRR) Chiral Perturbation Theory, vital to resolving the chiral extrapolation problem in Lattice QCD.

• Invented a diagrammatic method for the transparent and rapid determination of chiral-expansion coefficients for quenched chiral perturbation theory.

• Created the Fat-Link Irrelevant Clover (FLIC) fermion action; an efficient lattice fermion operator with excellent scaling properties providing near-continuum results at finite lattice spacing and superior chiral properties enabling access to the light quark-mass regime.

• Designed and implemented the first analysis of the mass and renormalization functions of the Overlap-quark propagator. The nature of the AsqTad propagator has also been established with these techniques.

• Resolved the momentum dependence of the Landau gauge gluon propagator in the infrared regime via lattice QCD simulations.

• Designed and implemented the first complete O(a²)-improved analysis of the Landau gauge gluon propagator, including an O(a²) -improved action and O(a²)-improved Landau gauge fixing.

• Illustrated the essential role of chiral nonanalytic behavior in extrapolations of hadronic observables to the light quark-mass regime.

• Developed and tested new parity-projection methods for exploring N* physics in lattice gauge theory. Implemented the first analysis of N*1/2^- and N*3/2^- low-lying odd-parity nucleon states in lattice QCD.

• Identified an approach establishing the scalar and vector self-energies of the nucleon in finite density nuclear matter, independent of the problematic scalar-scalar four-quark condensates.

• Resolved the behavior of the ρ-meson mass and decay constant in finite density nuclear matter as extracted from QCD Sum Rules.

• Designed and implemented the first Monte-Carlo based uncertainty analysis for the QCD Sum Rule approach to QCD, thus determining the predictive ability of the technique.

• Solved the ''pion-proton charge radius problem'' in lattice QCD by introducing the use of chiral perturbation theory in extrapolating to physical quark masses.

• Implemented the first ab initio investigation of octet and decuplet baryon structure and their electromagnetic transitions. This work was first to emphasize the environment sensitivity of individual quark sector contributions to form factors which are now finally being resolved at Jefferson Laboratory in the USA.

• Implemented the first ab initio investigation of octet and decuplet baryon structure and their electromagnetic transitions. This work was first to emphasize the environment sensitivity of individual quark sector contributions to form factors which are now finally being resolved at Jefferson Laboratory in the USA.

• Established a formalism for isolating and extracting multipole form factors of octet and decuplet baryons, and their electromagnetic transitions.

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