Heterotic-Type I Dual Pairs, Rigid Branes and Broken Susy

Understand

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.