A Modern View of Perturbative QCD and Application to Heavy Quarkonium Systems

Perturbative QCD has made significant progress over the last few decades. In the first part, we present an introductory overview of perturbative QCD as seen from a modern viewpoint. We explain the relation between purely perturbative predictions and predictions based on Wilsonian effective field theories. We also review progress of modern computational technologies and discuss intersection with frontiers of mathematics. Analyses of singularities in Feynman diagrams play key roles towards developing a unified view. In the second part, we discuss application of perturbative QCD, based on the formulation given in the first part, to heavy quarkonium systems and the interquark force between static color charges. We elucidate impacts on order Lambda_QCD physics in the quark mass and interquark force, which used to be considered inaccessible by perturbative QCD.Comment: 44 pages, 26 figures; lecture given at "QCD Club'' at Univ. Tokyo, June 201

Renormalon Cancellation and Perturbative QCD Potential as a Coulomb+Linear Potential

Recently evidence has been found that the perturbative QCD potential agrees well with phenomenological potentials and lattice computations of the QCD potential. We review the present status of the perturbative QCD potential and theoretical backgrounds. We also report our recent analysis which shows analytically, on the basis of renormalon dominance picture, that the perturbative QCD potential quickly ``converges'' to a Coulomb-plus-linear form. The Coulomb-plus-linear potential can be computed systematically as we include more terms of the perturbative series; up to three-loop running (our current best knowledge), it shows a convergence towards lattice results. e.g. At one-loop running, the linear potential is sigma*r with sigma = (2*pi*C_F/beta0) Lambda_MSbar^2.Comment: Minor changes, References added; 11 pages, 7 figures, Talk given at "Confinement 2003", Riken, Tokyo, July 200

New Method for Exact Calculation of Green Functions in Scalar Field Theory

We present a new method for calculating the Green functions for a lattice scalar field theory in $D$ dimensions with arbitrary potential $V(\phi)$. The method for non-perturbative evaluation of Green functions for $D \! = \! 1$ is generalized to higher dimensions. We define ``hole functions'' $A^{(i)}~(i=0,1,2,\cdots,N \! -\! 1)$ from which one can construct $N$-point Green functions. We derive characteristic equations of $A^{(i)}$ that form a {\it finite closed} set of coupled local equations. It is shown that the Green functions constructed from the solutions to the characteristic equations satisfy the Dyson-Schwinger equations. To fix the boundary conditions of $A^{(i)}$, a prescription is given for selecting the vacuum state at the boundaries.Comment: PostScript file of Figures is attached in the end. Search for the strings "cut here