A Perturbatively Stable Non-Supersymmetric String Model with AdS Vacuum

We present a construction of a perturbatively stable non-supersymmetric type II closed string model in four dimensions. It is based on a freely acting Scherk-Schwarz Z2-deformation of a supersymmetric construction which is recovered in appropriate decompactification limits. The model exhibits also the so-called misaligned supersymmetry with alternating signs for the number difference between bosons and fermions at successive mass levels. The tree-level spectrum is tachyon free for any value of the radii and moduli. At one loop level, the scalar potential has a non-supersymmetric minimum at the self-dual (free fermionic) point with negative energy, around which all tree-level massless scalars acquire positive masses. The model is thus non-supersymmetric and perturbatively stable.