### April 17, 2005

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The Fall and Rise of Lattice QCD: High-Precision Lattice QCD
Confronts Experiment

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G. Peter Lepage

Prof. of Physics and Dean of Arts and Sciences

Cornell University

Lattice QCD, the fundamental theory of strong interactions and
subnuclear structure, was 30 years old last year. Until 2000, however,
attempts to analyze the theory numerically were stymied by our
inability to simulate efficiently the effects of quark vacuum
polarization. Consequently most results had uncontrolled systematic
errors of order 15-30% or more. Algorithmic and theoretical
developments in the late 1990s led to a breakthrough that makes
high-precision, nonperturbative QCD calculations possible for the
first time in history. These developments have important implications
for heavy-quark and Standard Model physics, and potentially also for
our understanding of physics beyond the Standard Model. It also is a
major development in the history of quantum field theory. This
seminar is a non-technical review of the conceptual ideas behind this
revolutionary development in strong-interaction physics, together
with a survey of the current impact on theoretical and experimental
particle physics, and prospects for the future.