  The moduli space of toroidal type I vacua, which are consistent at the
non-perturbative level, consists of independent branches characterized by the
number (0, 16 or 32) of rigid branes sitting on top of orientifold planes. This
structure persists also when supersymmetry is spontaneously broken a la
Scherk-Schwarz. We show that all the components of the moduli space in
dimension $D\ge 5$ indeed admit heterotic dual components, by explicitly
constructing heterotic-type I dual pairs with the rank of the gauge group
reduced by 0, 8 or 16 units. In the presence of spontaneous breaking of
supersymmetry, the dual pairs we consider are also free of tachyonic
instabilities at the one-loop level, provided the scale of supersymmetry
breaking is lower than the string scale.

High Energy Physics - Theory