3-BRANES AND 5-BRANES IN N=1 DUAL STRING PAIRS

In this note we show that in dual N = 1 string vacua provided by the h eterotic string on an elliptic Calabi-Yau together with a vector bundl e respectively F-theory on Calabi-Yau fourfold the number of heterotic fivebranes necessary for anomaly cancellation matches the number of F -theory threebranes necessary for tadpole cancellation. This extends t o the general case the work of Friedman, Morgan and Witten, who treate d the case of embedding a heterotic E-8 x E-8 bundle, leaving no unbro ken gauge group, where one has a smooth Weierstrass model on the F-the ory side. (C) 1998 Elsevier Science B.V.