| dc.description |
We investigate unitarity of W<sup>+</sup>W<sup>−</sup> scattering in the context of theory space models of the form U(1) × [SU(2)]<sup>N</sup> × SU(2)<sub>N+1</sub>, which are broken down to U(1)<sub>EM</sub> by non-linear Σ fields, without the presence of a physical Higgs Boson. By allowing the couplings of the U(1) and the final SU(2)<sub>N+1</sub> to vary, we can fit the W and Z masses, and we find that the coefficient of the term in the amplitude that grows as E<sup>2</sup>/m<sub>W</sub><sup>2</sup> at high energies is suppressed by a factor of (N+1)<sup>−2</sup>. In the N+1→∞ limit the model becomes a 5-dimensional SU(2) gauge theory defined on an interval, where boundary terms at the two ends of the interval break the SU(2) down to U(1)<sub>EM</sub>. These boundary terms also modify the Kaluza-Klein (KK) mass spectrum, so that the lightest KK states can be identified as the W and Z bosons. The T parameter, which measures custodial symmetry breaking, is naturally small in these models. Depending on how matter fields are included, the strongest experimental constraints come from precision electroweak limits on the S parameter. |
