DYONIC P-BRANES FROM SELF-DUAL (P+1)-BRANES

The ''electromagnetic'' SE(2; Z) duality group in spacetime dimension D = 4k can be given a Kaluza-Klein interpretation in D = 4k + 2 as the modular group of a compactifying torus. We show how dyonic 2(k - 1)-b ranes in D = 4k can be interpreted as self-dual (2k - 1)-branes in D = 4k + 2 wound around the homology cycles of tile torus. In particular, dyons of the D = 4 N = 4 heterotic string theory are interpreted as w inding modes of a D = 6 self-dual string, while D = 8 dyonic membranes are interpreted as wound 3-branes of D = 10 IIB superstring theory. W e also discuss the T-dual IIA interpretations of D = 8 dyonic membrane s.