Extra Dimension Kaluza-Klein Excitations and Electroweak Symmetry Breaking

We review the possibilities that the Kaluza-Klein excitations of graviton states induce electroweak symmetry breaking and that electroweak symmetry breaking could have a large impact on KK phenomenology. In one popular approach [1] to extra dimensions with length scales far larger than the inverse Planck mass [2], ordinary particles are confined on a brane (having three spatial dimensions) with gravity propagating in the bulk. This talk summarizes our paper [3] showing that the KK modes could have a dramatic impact on electroweak symmetry breaking, possibly providing the EWSB mechanism and how, in turn, EWSB could have a large impact on KK phenomenology. We consider a theory with δ extra dimensions of compactified size L. In the standard approach [4, 5], a linearized approximation is employed in which the metric tensor is expanded to first order in κ = √ 16πGN about the flat-space limit to obtain an effective Lagrangian and corresponding equations of motion for the KK modes and Standard Model fields on the brane. Focusing on the Higgs sector, there are three key components to the resulting overall Lagrangian. (a) The Higgs Lagrangian, LΦ, containing an arbitrary Higgs potential −V (Φ) that for simplicity we take to be a function of a single real Higgs scalar field Φ. The corresponding contribution to the energy momentum tensor is Tμν = ημνV (Φ). (b) We also have the massive KK states, with masses m~n2 = 4π2~n2 L2 , where ~n = (n1, n2, . . . , nδ), and corresponding mass-term To appear in the Proceedings of the 7th International Symposium on Particles, Strings and Cosmology, PASCOS 99. Presented by J. Gunion