Top and bottom: A brane of their own

Abstract

We consider extra dimensional descriptions of models where there are two separate strongly interacting sectors contributing to electroweak symmetry breaking (“topcolor” type models). In the extra dimensional picture there would be two separate (anti-de Sitter) bulks meeting on the Planck brane, with each bulk having its own corresponding IR (TeV) brane. Sources for electroweak symmetry breaking can then be localized on both of these IR branes, while the different generations of fermions may be separated from each other. We describe the modes propagating in such a setup, and consider the cases where the electroweak symmetry breaking on either of the two IR branes come either from a higgsless scenario (via boundary conditions) or a (top-)Higgs. We show that the tension that exists between obtaining a large top quark mass and the correct value of the Zb¯b couplings in ordinary higgsless models can be largely relieved in the higgsless—top-Higgs versions of the two IR brane models. This may also be true in the purely higgsless—higgsless case, however since that model is necessarily in the strongly coupled regime the tree-level results for the properties of the third generation may get large corrections. A necessary consequence of such models is the appearance of additional pseudo-Goldstone bosons (“top-pions”), which would be strongly coupled to the third generation.