A symmetry for Z psibar psi

LEANDRO DA ROLD

Rehovot

Seminario; Seminar of the Department of Particle Physics and Astrophysics of the Weizmann Institute of Science; 2015

Weizmann Institute

We show that a subgroup of the custodial symmetry O(3) that protects ρ from radiative corrections can also protect the Zbb coupling. Thisallows 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 → bb. We show that when this symmetry protects Zbb it cannot simultaneously protect Zt t and W t b. Therefore one can expectto measure sizable deviations from the SM predictions of these couplings at future collider experiments. We also show under what circumstances ZbR bR can receive corrections in the right direction to explain the anomaly in the LEP/SLD forward?backward asymmetry Ab .