Eur. Phys. J. C (2011) 71: 1786
https://doi.org/10.1140/epjc/s10052-011-1786-z

Regular Article - Theoretical Physics

Unitarity in Dirichlet Higgs model

¹ Department of Physics, Kobe University, Kobe, 657-8501, Japan
² Department of Physics, Osaka University, Osaka, 560-0043, Japan
³ Theory Division, CERN, 1211, Geneva 23, Switzerland

^* e-mail: odakin@phys.sci.osaka-u.ac.jp
^** e-mail: kin-ya.oda@cern.ch

Received: 20 December 2010
Revised: 11 August 2011
Published online: 8 November 2011

Abstract

We show that a five-dimensional Universal Extra Dimension model, compactified on a line segment, is consistently formulated even when the gauge symmetry is broken solely by non-zero Dirichlet boundary conditions on a bulk Higgs field, without any quartic interaction. We find that the longitudinal W ⁺ W ⁻ elastic scattering amplitude, under the absence of the Higgs zero mode, is unitarized by exchange of infinite towers of KK Higgs bosons. Resultant amplitude scales linearly with the scattering energy , exhibiting five-dimensional nature. A tree-level partial-wave unitarity condition is satisfied up to 6.7 (5.7) TeV for the KK scale m _KK=430 (500) GeV, favored by the electroweak data within 90% CL.