Duality and combinatorics of long strings in ADS(3)

The counting of long strings in ADS(3), in the context of type IIB string t heory on ADS(3) x S-3 x T-4, is used to exhibit the action of the duality g roup O(5, 5; Z), and in particular its Weyl subgroup S-5 x Z(2), in the non -perturbative phenomena associated with continuous spectra of states in the se backgrounds. The counting functions are related to states in Fock spaces . The symmetry groups also appear in the structure of compactifications of instanton moduli spaces on T-4. (C) 2000 Elsevier Science B.V. All rights r eserved.