DUALITY OF N=2 HETEROTIC-TYPE-I COMPACTIFICATIONS IN 4 DIMENSIONS

We discuss type I-heterotic duality in four-dimensional models obtaine d as a Coulomb phase of the six-dimensional U(16) orientifold model co mpactified on T-2 with arbitrary SCT(16) Wilson lines, We show that Ka hler potentials, gauge threshold corrections and the infinite tower of higher derivative F-terms agree in the limit that corresponds to weak coupling, large T-2 heterotic compactifications. On the type I side, all these quantities are completely determined by the spectrum of N = 2 BPS states that originate from D = 6 massless superstring modes. (C) 1997 Elsevier Science B.V.