Non-minimal Higgs content in standard-like models from D-branes at a Z_N singularity

Abstract

We show that attempts to construct the standard model, or the MSSM, by placing D3-branes and D7-branes at a Z_N orbifold or orientifold singularity all require that the electroweak Higgs content is non-minimal. For the orbifold the lower bound on the number n(H) + n({\bar{H}}) of electroweak Higgs doublets is the number n(q^c_L)=6 of quark singlets, and for the orientifold the lower bound can be one less. As a consequence there is a generic flavour changing neutral current problem in such models.

LaTeX, 14 pages. A paragraph generalising the results to left-right symmetric models has been added