We show that a subgroup of the custodial symmetry O (3) that protects Δρ from radiative corrections can also protect the Z b over(b, ̄) coupling. This allows one to build models of electroweak symmetry breaking, such as higgsless, little Higgs or 5D composite Higgs models, that are safe from corrections to Z → b over(b, ̄). We show that when this symmetry protects Z b over(b, ̄) it cannot simultaneously protect Z t over(t, ̄) and W t over(b, ̄). Therefore one can expect to measure sizable deviations from the SM predictions of these couplings at future collider experiments. We also show under what circumstances Z bR over(b, ̄)R can receive corrections in the right direction to explain the anomaly in the LEP/SLD forward-backward asymmetry AFBb. © 2006 Elsevier B.V. All rights reserved.
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|Publication status||Published - 28 Sep 2006|