My research is in elementary particle theory. Much of it uses the computational methods of lattice gauge theory and is done in collaboration with researchers at nine other institutions. This collaboration, known as MILC, tackles a wide range of problems in strong and weak interactions and high-temperature physics. Our lattice configurations, which take into account the effects of three flavors of light dynamical quarks, are freely available to researchers world-wide. MILC code is also available; it runs on a wide range of massively parallel computers as well as on individual workstations. Recent computations, many of which are collaborative efforts with the Fermilab Lattice Group, have been done at the National Institute for Computational Science (NICS), the Pittsburgh Supercomputing Center (PSC), the San Diego Supercomputing Center (SDSC) , the Texas Advanced Computing Center (TACC), the National Center for Supercomputing Applications (NCSA), and using the dedicated USQCD resources, primarily at Fermilab .

A major focus of my recent work has been analytic work on low energy effective theories of QCD, namely chiral perturbation theory . My calculations seek to bridge the gap between numerical lattice calculations and the real world of continuum particle physics. Building on work of Lee and Sharpe, graduate student Christopher Aubin and I developed "staggered chiral perturbation theory" (SChPT) which adjusts the results of continuum chiral perturbation theory to take into account discretization errors introduced by staggered fermions on the lattice. SChPT was later extended to heavy-light mesons by Aubin and me, to baryons by student Jon Bailey, and to the group SU(2) by student Xining Du.

Using staggered chiral perturbation theory allows the MILC collaboration to obtain precise results for various hadronic quantities. See, for example, an extrapolation of MILC data for the pion decay constant to the physical values of the u and d quark masses and to the continuum.

The same methods make possible the determination of key parameters of the weak-interaction sector of the Standard Model, by combining experimental measurements of hadronic decay rates or form factors with lattice evaluations of the strong-interaction effects in these hadrons. For example, in Phys. Rev. D79, 054507 (2009) a lattice calculation of the form factor for the semileptonic decay of B to pi results in a determination of the fundamental parameter Vub. As a check, comparison of the form factor shape from experiment and theory shows excellent agreement. Such calculations constrain the Standard Model, and provide possible windows into new physics beyond the Standard Model.

Last updated March 9, 2012