This proposal requests a supplement to grant PHY 0456691 to fund a 5-year postdoc in lattice gauge theory at the University of Utah. This request is part of a general scheme developed by the lattice gauge theory community to fund a 5-year postdoc in the field on a competitive basis. The proposed research is to determine matrix elements of weak interaction processes important for understanding QCD.
. The work involved solving and investigating quantum chromodynamics, the theory of interacting quarks and gluons, by using high-performance supercomputers. Such projects are major undertakings requiring team work for carrying out the computational design, developing and validating the algorithms and computer codes, managing the computational campaigns, and analyzing and interpreting the results. Much of these calculations are carried out on NSF XSEDE national computer facilities. Much of our research includes some 20 collaborators at eight US universities and laboratories. Several projects were completed under this grant. Here we describe highlights. One project studied the behavior of quark-gluon matter at extreme temperatures and densities, conditions that it is believed existed in the first moments of the life of the universe. The same conditions are thought to be recreated in microcosm during collisions of heavy ions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. Through numerical calculation we were able to simulate these conditions and determine (1) the temperature at which ordinary matter becomes a quark-gluon plasma, (2) the equation of state, an important thermodynamic quantity characterizing the plasma, and (3) the expected thermal fluctuations in charges and other experimentally measurable quantities. These results are needed for interpreting the results of experimental measurement, and they provide insight into conditions in the very early universe. A second project studied the low-lying energy levels of charmonium, a bound state of a charm quark and a charm antiquark. These energy levels are well measured in accelerator experiments, so the primary purpose of the calculation is to validate the methodology. We demonstrated that with our methods, we could reproduce the known energy levels of the low-lying states at the world's best precision. These results allow us to use the same methods with confidence to make predictions where discoveries are yet to be made. Our knowledge of the fundamental interactions and particles in nature is embodied in the modestly called "standard model". Most of us believe that the model is incomplete and that a deeper, more fundamental theory remains to be discovered. Discovering it is the principal purpose of the Large Hadron Collider (LHC). It is believed that we will first find clues about the more fundamental interactions by finding subtle disagreements between the predictions of the standard model and results of experimental measurement. This effort requires high precision both on the part of theorey and experiment. Thus far, the precision of theoretical prediction has fallen behind that of experiment, which has held up progress. Thus, one of our highest priorities has been refining, through numerical calculation, the theoretical precision. We have achieved the best theoretical results thus far for several key quantities, namely the constants in the standard model that characterize transitions between the heavier and the lighter quarks, and we continue to press for a precision that keeps pace with experiment. A side benefit of this work is the creation of a large library of "gauge configuration" files that will form the basis for a long series of studies of quantum chromodynamics by us and others. We also have developed and contributed to a large community code base for such calculations. These codes use state of the art algorithms and methods and, in working with industry, we help drive innovation in computer design for scientific computation. We make all of these products freely available to other researchers. Our gauge configuration files and computer codes are used by many groups both in the US and abroad. Finally, our postdoctoral research associates and students develop skills in high-performance computation and numerical analysis. These skills are of high value in the technological workplace. Thus in a modest way we contribute to the economic competitiveness of the nation.
