Tachyon-free non-supersymmetric type I string vacua from brane-antibrane systems

by Angel M. URANGA (CERN)

Wednesday 17 Nov 1999, 14:00 → 14:15 Europe/Zurich

TH Auditorium (CERN)

Compactifications of Type I string vacua to four dimensions have several phenomenologically interesting features. In particular, they provide an explicit realization of consistent models where gauge theory sectors can be localized on D-branes, while gravity and other fields propagate over all of spacetime. In this talk I will first review the construction of toroidal orbifolds of type I string theory, and discuss their consistency conditions (cancellation of tadpoles). I will show it is possible to construct consistent models which contain D-branes and anti-D-branes, but are nevertheless stable against decay by brane-antibrane annihilation. These models are non-supersymmetric but free of tachyons. In many examples, supersymmetry is preserved at lowest order in the bulk and in D-brane 'visible' sectors, while sypersymmetry is broken at the string scale in 'hidden' anti-D-brane sectors. Models with realistic 'visible' sectors can be easily constructed. Finally, these configurations raise interesting questions concerning the dynamics of the compactification moduli and the dilaton, which have non-trivial potentials due to the lack of supersymmetry.