  We analyze a recently constructed class of D-brane theories with the fermion
spectrum of the SM at the intersection of D6-branes wrapping a compact toroidal
space. We show how the SM Higgs mechanism appears as a brane recombination
effect in which the branes giving rise to U(2)_L \times U(1) recombine into a
single brane related to U(1)_{em}. We also show how one can construct D6-brane
models which respect some supersymmetry at every intersection. These are
quasi-supersymmetric models of the type introduced in hep-th/0201205 which may
be depicted in terms of SUSY-quivers and may stabilize the hierarchy between
the weak scale and a fundamental scale of order 10-100 TeV present in low
string scale models. Several explicit D6-brane models with three generations of
quarks and leptons and different SUSY-quiver structure are presented. One can
prove on general grounds that if one wants to build a (factorizable) D6-brane
configuration with the SM gauge group and N = 1 SUSY (or quasi-SUSY), also a
massless (B-L) generator must be initially present in any model. If in addition
we insist on lef- and right-handed fermions respecting the same N=1 SUSY, the
brane configurations are forced to have intersections giving rise to Higgs
multiplets, providing for a rationale for the very existence of the SM Higgs
sector.
