  It is known that chiral fermions naturally appear at certain intersections of
branes at angles. Motivated by this fact, we propose a string scenario in which
different standard model gauge interactions propagate on different
(intersecting) brane worlds, partially wrapped in the extra dimensions. Quarks
and leptons live at brane intersections, and are thus located at different
positions in the extra dimensions. Replication of families follows naturally
from the fact that the branes generically intersect at several points. Gauge
and Yukawa couplings can be computed in terms of the compactification radii.
Hierarchical Yukawa couplings appear naturally, since amplitudes involving
three different intersections are proportional to exp{-A_{ijk}}, where A_{ijk}
is the area of a string world-sheet extending among the 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 a set of discrete symmetries arising
from world-sheet selection rules, exact to all orders in perturbation theory.
The scenario has some distinctive features like the presence of 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 standard SU(2) x U(1) Higgs doublets, and we propose that they
induce electroweak symmetry breaking in a somewhat novel way. Specific string
models with D4-branes wrapping on T^2 x (T^2)^2/Z_N, leading to three-family
semirealistic spectra, are presented, in which the above properties are
exemplified.

High Energy Physics - Phenomenology;High Energy Physics - Theory