Systematics of one-loop Yang-Mills diagrams from bosonic string amplitudes

We present a general algorithm to compute off-shell, one-loop multigluon Gr een functions using bosonic string amplitudes. We identify and parametrize the regions in the space of moduli of one loop Riemann surfaces that contri bute to the field theory limit of string amplitudes. Each of these regions can be precisely associated with a Feynman-like scalar graph with cubic and quartic vertices, whose lines represent the joint propagation of ghosts an d gluons. We give a procedure to compute the contribution of each graph to a gluon Green function, for arbitrarily polarized off-shell gluons, reducib le and irreducible diagrams, planar and non-planar topologies. Explicit exa mples are given For up to six gluons. (C) 2001 Published by Elsevier Scienc e B.V.