STRING UNIFICATION, UNIVERSAL ONE-LOOP CORRECTIONS AND STRONGLY COUPLED HETEROTIC STRING THEORY

We derive the universal threshold corrections in heterotic string theo ry including a continuous Wilson line, Unification of gauge and gravit ational couplings is shown to be possible even within perturbative str ing theory, The relative importance of gauge group dependent and indep endent thresholds on unification is clarified, Equipped with these res ults we can then attempt an extrapolation to the strongly coupled hete rotic string - M-theory, We argue that such an extrapolation might be meaningful because of the holomorphic structure of the gauge coupling function and the close connection of the threshold corrections to the anomaly cancellation mechanism. (C) 1997 Elsevier Science B.V.