Standard model at intersecting D5-branes: lowering the string scale Original Research Article

Recently a class of type IIA orientifold models was constructed yielding just the fermions of the SM at the intersections of D6-branes wrapping a 6-torus. We generalize that construction to the case of type IIB compactified on an orientifold of T4×(C/ZN) with D5-branes intersecting at angles on T4. We construct explicit models in which the massless fermion spectrum is just the one of a three-generation standard model. One of the motivations for these new constructions is that in this case there are 2 dimensions which are transverse to the SM D5-brane configuration. By making those two dimensions large enough one can have a low string scale Ms of order 1–10 TeV and still have a large MPlanck in agreement with observations. From this point of view, these are the first explicit D-brane string constructions where one can achieve having just the fermionic spectrum and gauge group of the SM embedded in a Low String Scale scenario. The cancellation of U(1) anomalies turns out to be quite analogous to the toroidal D6-brane case and the proton is automatically stable due to the gauging of baryon number. Unlike the D6-brane case, the present class of models has N=0 SUSY both in the bulk and on the branes and hence the spectrum is simpler.