• accoppiamento minimale
• intersecting branes
• string scattering

The property of minimal coupling is investigated in the
low energy limit of string theory. Effective lagrangians for
ge\-ne\-ric theories presenting electroweak symmetry breaking are
studied, with particular emphasis on effective Higgs-gauge vector
interactions. Higgs fields are represented by open string states
localized at brane intersections and the four-dimensional theory
is obtained from the ten-dimensional one compactifying on a six
torus. The coefficient of the six-dimensional operator
HHFF (where H is Higgs field and F the field strength) is computed to first order in
the string loop expansion. This operator does not emerge at tree
level, in accord with the hypothesis of minimal coupling. It does
emerge at one loop, however, which shows the absence of hidden
symmetries which protect it