Intersecting brane worlds

Chiral fermions naturally appear at intersections of branes at angles. We p ropose a string scenario in which different SM gauge interactions propagate on different (intersecting) brane worlds, partially wrapped in the extra d imensions. Quarks and leptons live at brane intersections, located at diffe rent positions in the extra dimensions. Replication of families follows bec ause branes generically intersect at several points. Gauge and Yukawa coupl ings can be computed in terms of the compactification radii. Yukawa couplin gs are hierarchical, proportional to exp A, where A is the area of a string world-sheet extending among three intersections. The models are non-supers ymmetric but the string scale may be lowered down to 1-10 TeV. The proton i s however stable due to discrete symmetries, exact in perturbation theory. The scenario has KK, winding and other new excited states ('gonions'), with masses below the string scale and accessible to accelerators. The models c ontain scalar tachyons with the quantum numbers of SM Higgs doublets, and w e propose that they induce electroweak symmetry breaking in a novel way. We present specific string models with the above properties, built from D4-br anes wrapping on T-2 X (T-2)(2)/Z(N), and leading to 3-family semirealistic spectra.