Higgsless ElectroWeak symmetry breaking

Abstract

We present Higgsless models where the electroweak symmetry breaking is achieved by suitable boundary conditions for the gauge fields. We study tree level corrections to precision electroweak physics. Such models inherit from their similarity with technicolor theories a large contribution to the oblique parameters, S in particular. We show that it is possible to suppress S using brane induced kinetic terms and unequal left-right bulk gauge couplings, paying the price of heavy KK modes. In the allowed region, they are eventually ineffective in restoring perturbative unitarity in W scattering above 2 TeV. We show that such problem can be easily solved by delocalizing the light fermions in the bulk, which lowers their couplings to the KK gauge bosons. We conclude by presenting some extra dimensional descriptions of models where there are two separate strongly interacting sectors contributing to electroweak symmetry breaking ("topcolor" type models). We show that the tension that exists between obtaining a large top quark mass and the correct value of the Zbb couplings in ordinary higgsless models can be largely relieved.