Nonminimal universal extra dimensions

In this paper, we investigate the phenomenological implications of boundary localized terms (BLTs) in the model of universal extra dimensions (UED). In particular, we study the electroweak Kaluza-Klein mass spectrum resulting from BLTs and their effect on electroweak symmetry breaking via the five-dimensional Higgs mechanism. We find that the addition of BLTs to massive five-dimensional fields induces a nontrivial extra-dimensional profile for the zero and nonzero Kaluza-Klein (KK) modes. Hence BLTs generically lead to a modification of standard model parameters and are therefore experimentally constrained, even at tree level. We study standard model constraints on three representative nonminimal UED models in detail and find that the constraints on BLTs are weak. On the contrary, nonzero BLTs have a major impact on the spectrum and couplings of nonzero KK modes. For example, there are regions of parameter space where the lightest Kaluza-Klein particle is either the Kaluza-Klein Higgs boson or the first KK mode of the ${W}^{3}$.