SUPERSTRING THRESHOLD CORRECTIONS TO YUKAWA COUPLINGS

A general method of computing string corrections to the Kahler metric and Yukawa couplings is developed at the one-loop level for a general compactification of the heterotic superstring theory. It also provides a direct determination of the so-called Green-Schwarz term. The matte r metric has an infrared divergent part which reproduces the field-the oretical anomalous dimensions, and a moduli-dependent part which gives rise to threshold corrections in the physical Yukawa couplings. Expli cit expressions are derived for symmetric orbifold compactifications.