Intersecting brane worlds

Chiral fermions naturally appear at intersections of branes at angles. We propose a string scenario in which different SM gauge interactions propagate on different (intersecting) brane worlds, partially wrapped in the extra dimensions. Quarks and leptons live at brane intersections, located at different positions in the extra dimensions. Replication of families follows because branes generically intersect at several points. Gauge and Yukawa couplings can be computed in terms of the compactification radii. Yukawa couplings are hierarchical, proportional to exp A, where A is the area of a string world-sheet extending among three intersections. The models are non-supersymmetric but the string scale may be lowered down to 1-10 TeV. The proton is 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 contain scalar tachyons with the quantum numbers of SM Higgs doublets, and we propose that they induce electroweak symmetry breaking in a novel way. We present specific string models with the above properties, built from D4-branes wrapping on T-2 X (T-2)(2)/Z(N), and leading to 3-family semirealistic spectra.