The Zbb vertex in a left-right model

We consider the one-loop corrections to theZbb vertex in a CP-conserving left-right model (LRM), viz. a model with gauge group SU(2)(L)xSU(2)(R)xU(1). We allow the gauge coupling constants of SU(2)(L) and SU(2)(R) to be different. The spontaneous symmetry breaking is accomplished only by doublets and/or singlets of SU(2)(L) and SU(2)(R). The lightest massive neutral gauge boson of our LRM is assumed to have the same Yukawa couplings to bottom-quark pairs as the Z of the Standard Model (SM); this assumption has the advantage that, then, the infrared divergences automatically cancel down in the subtraction of the Zbb vertex in the SM from the same vertex in the LRM. We effect a proper renormalization of the Zbb vertex and check explicitly both its gauge invariance and the cancellation of all the ultraviolet divergences. We find out that a LRM with the above assumptions cannot achieve a better fit to the Zbb vertex than a multi-Higgs extension of the SM, viz. both models can only achieve a decent fit when one admits scalar particles with very low masses less than or similar to 50 GeV. This is true even when we allow for markedly different gauge coupling constants of SU(2)(L) and SU(2)(R).(c) 2023TheAuthors.Published by Elsevier B.V.This is an open access article under the CC BY license(http://creativecommons.org/licenses/by/4.0/).