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Type-I strings on magnetised orbifolds and brane transmutation. (English) Zbl 1031.81579
Summary: In the presence of internal magnetic fields, a D9 brane can acquire a D5 (or anti-D5) R-R charge, and can therefore contribute to the corresponding tadpole. In the resulting vacua, supersymmetry is generically broken and tachyonic instabilities are present. However, suitable choices for the magnetic fields, corresponding to self-dual configurations in the internal space, can yield new chiral supersymmetric vacua with gauge groups of reduced rank, where the magnetic energy saturates, partly or fully, the negative tension of the $$O5_+$$ planes. These models contain Green-Schwarz couplings to untwisted R-R forms not present in conventional orientifolds.

##### MSC:
 81T30 String and superstring theories; other extended objects (e.g., branes) in quantum field theory
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