Exact Standard model Structures from Intersecting D5-Branes
  We discuss the appearance of non-supersymmetric compactifications with exactly the Standard Model (SM) at low energies, in the context of IIB orientifold constructions with   D5 branes intersecting at angles on the $T^4$ tori, of the orientifold of $T^4 \times (\C /Z_N)$.   We discuss constructions where the Standard Model embedding is considering within four, five and six stacks of D5 branes. The appearance of the three generation observable Standard Model at low energies is accompanied by a gauged baryon number, thus ensuring automatic proton stability. Also, a compatibility with a low scale of order TeV is ensured by having a two dimensional space transverse to all branes. The present models complete the discussion of some recently constructed four stack models of D5 branes with the SM at low energy. By embedding the four, five and six stack Standard Model configurations into quiver diagrams, deforming them around the QCD intersection numbers, we find a rich variety of vacua that may have exactly the Standard Model at low energy. Also by using brane recombination on the U(1)'s, we show that the five and six vacua flow into their four stack counterparts. Thus string vacua with five and six stack deformations are continuously connected to the four stack vacua. 
Christos Kokorelis