A Feynman-graph generator for any order of coupling constants

A computer program has been developed which generates Feynman graphs automatically for scattering and decay processes in non-Abelian gauge theory of high-energy physics. A new acceleration method is presented for both generating and eliminating graphs. This method has been shown to work quite efficiently for any order of coupling constants in any kind of theoretical model. A utility program is also available for drawing generated graphs. These programs consist of the most basic parts of the GRACE system, which is now used to automatically calculate tree and one-loop processes.Comment: 41 pages, Style file epsf.sty, ftp://ftp.kek.jp/kek/minami/gr

Energy Loss and Straggling of Low-velocity Atoms in Matter

Based on the dielectric function method, the analytical formulas are presented for the energy loss and the straggling of low-velocity heavy atoms with atomic number Z_1 passing through the degenerate electron gas. The spatial sizeΛ of the electron cloud on projectiles is newly determined according to the statistical variational method by taking into account the static screening effect of conduction electrons. The analytical formulas obtained here have the Z_1-dependences different from those by the existing theories in spite of the same velocity dependence. It is found that the screening effect on Λ enlarges thelectronic stopping of the media by a constant value regardless of Z_1