TOWARDS MASS DEFORMED N=4 SO(N) AND SP(K) THEORIES FROM BRANE CONFIGURATIONS

We study the introduction of orientifold 6-planes in the type IIA bran e configurations known as elliptic models. The N= 4 SO(n) and Sp(k) th eories softly broken to N = 2 through a mass for the adjoint hypermult iplet can be realized in this framework in the presence of two orienti fold planes with opposite RR charge. A large class of beta = 0 models is served for vanishing sum of hypermultiplet masses by embedding the type IIA configuration into M-theory. We also End a geometric interpre tation of Montonen-Olive duality based on the properties of the curves . We make a proposal for the introduction of non-vanishing sum of hype rmultiplet masses in a sub-class of models. In the presence of two neg atively charged orientifold planes and four D6-branes other interestin g beta = 0 theories are constructed, e.g. Sp(k) with four flavours and a massive antisymmetric hypermultiplet. We comment on the difficultie s in obtaining the curves within our framework due to the arbitrary po sitions of the D6-branes, (C) 1998 Elsevier Science B.V.