Aspects of space-time dualities

Duality groups of Abelian gauge theories on four manifolds and their reduction to two dimensions are considered. The duality groups include elements that relate different space-times in addition to relating different gauge-coupling matrices. We interpret (some of) such dualities as the geometrical symmetries of compactified theories in higher dimensions. In particular, we consider compactifications of a (self-dual) 2-form in 6 - D, and compactifications of a self-dual 4-form in 10 - D. Relations with a self-dual superstring in 6 - D and with the type IIB superstring are discussed.