Standard model compactifications of IIA Z3×Z3 orientifolds from intersecting D6-branes

We discuss the construction of chiral four-dimensional T6/(Z3×Z3) orientifold compactifications of IIA theory, using D6-branes intersecting at angles and not aligned with the orientifold O6 planes. Cancellation of mixed U(1) anomalies requires the presence of a generalized Green-Schwarz mechanism mediated by RR partners of closed string untwisted moduli. In this respect we describe the appearance of three quark and lepton family SU(3)C×SU(2)L×U(1)Y non-supersymmetric orientifold models with only the massless spectrum of the SM at low energy that can have either no exotics present and three families of νR's (A′-model class) or the massless fermion spectrum of the N=1 SM with a small number of massive non-chiral colour exotics and in one case with extra families of νR's (B′-model class). Moreover we discuss the construction of SU(5), flipped SU(5) and Pati-Salam SU(4)c×SU(2)L×SU(2)R GUTS-the latter also derived from adjoint breaking-with only the SM at low energy. Some phenomenological features of these models are also briefly discussed. All models are constructed with the Weinberg angle to be 3/8 at the string scale.