D=4 chiral string compactifications from intersecting branes

Intersecting Dp-branes often give rise to chiral fermions living on their i ntersections. We study the construction of four-dimensional chiral gauge th eories by considering configurations of type II D(3+n)-branes wrapped on no ntrivial n-cycles on T(2n)x(R2(3-n)/Z(N)), for n=1, 2, 3. The gauge theorie s on the four noncompact dimensions of the brane world-volume are generical ly chiral and nonsupersymmetric. We analyze consistency conditions (RR tadp ole cancellation) for these models, and their relation to four-dimensional anomaly cancellation. Cancellation of U(1) gauge anomalies involves a Green -Schwarz mechanism mediated by RR partners of untwisted and/or twisted modu li. This class of models is of potential phenomenological interest, and we construct explicit examples of SU(3)xSU(2)xU(1) three-generation models. Th e models are nonsupersymmetric, but the string scale may be lowered close t o the weak scale so that the standard hierarchy problem is avoided. We also comment on the presence of scalar tachyons and possible ways to avoid the associated instabilities. We discuss the existence of (meta)stable configur ations of D-branes on 3-cycles in (T-2)(3), free of tachyons for certain ra nges of the six-torus moduli. (C) 2001 American Institute of Physics.