hep-ph/0305237
Gauge Theories on an Interval: Unitarity without a Higgs
Authors: C.Csaki, C.Grojean, H.Murayama, L.Pilo, J.Terning
We consider extra dimensional gauge theories on an interval. We first
review the derivation of the consistent boundary conditions (BC's) from
the action principle. These BC's include choices that give rise to
breaking of the gauge symmetries. The boundary conditions could be
chosen to coincide with those commonly applied in orbifold theories, but
there are many more possibilities. To investigate the nature of gauge
symmetry breaking via BC's we calculate the elastic scattering
amplitudes for longitudinal gauge bosons. We find that using a
consistent set of BC's the terms in these amplitudes that explicitly
grow with energy always cancel without having to introduce any
additional scalar degree of freedom, but rather by the exchange of
Kaluza--Klein (KK) gauge bosons. This suggests that perhaps the SM Higgs
could be completely eliminated in favor of some KK towers of gauge
fields. We show that from the low-energy effective theory perspective
this seems to be indeed possible. We display an extra dimensional toy
model, where BC's introduce a symmetry breaking pattern and mass
spectrum that resembles that in the standard model.