A symmetry for Z psibar psi, Model Building

LEANDRO DA ROLD

Rehovot

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

Weizmann Institute

We consider one of the most significant deviations from the Standard Model:the forward-backward asymmetry of the b-quark measured at leptonic colliders. We investigate the possibility to solve this discrepancy by introducing new physics at the TeV scale. We focus on models where the Higgs is a pseudo Nambu-Goldstone boson of a new strongly coupled sector with a global SO(5) symmetry broken spontaneously to SO(4). Besides the usual top partners, we introduce bottom partners in the representations 16 and 4 of SO(5) and show that they can improve significantly the fit by correcting the Zb ̄ couplings. We also estimate the corrections to the couplings at one-loop and obtain that the tree-level ones dominate and can give a reliable estimation. We find that the large shift required for ZbR ̄R leads to light custodians associated to the b-quark, similar to the top partners, as well as a rich phenomenology involving neutral interactions in the bottom-sector.