yyoon@fas.harvard.edu wrote:
> I just wonder if there are any known models that suggest higgs-like
> potential (Sigma a phi_a^2-constant)^2 in string phenomenology.[/color]
The D-term potential you write is completely natural in supersymmetric
gauge theories in four dimensions with at most eight supercharges (N <=
2). These gauge theories can be realized on a Hanany-Witten type brane
configuration in type IIA. Turning on the potential is accomplished by
introducing a Fayet-Iliopoulos parameter for the diagonal U(1) factor
of the gauge group. In the brane setup this corresponds to breaking
each color D4 on a flavor D6 and removing the two halves of the brane
configuration a finite distance in a flat direction of the internal
space. From this geometry it is clear that the Higgs phase emanates
from one specific point on the Coulomb branch and exists only if N_f >=
N_c.
Sixteen conserved supercharges in 4d (N=4) would force the potential to
be flat. Hence the restriction I mentioned.