The $Z b \bar b$ vertex in a left-right model

Duarte Fontes; Darius Jurčiukonis; Luís Lavoura

doi:10.1016/j.nuclphysb.2023.116373

paper

The $Z b b ˉ$ vertex in a left-right model

arXiv:2212.12075 · doi:10.1016/j.nuclphysb.2023.116373

Abstract

We consider the one-loop corrections to the $Z b b ˉ$ vertex in a $C P$ -conserving left--right model (LRM), $v i z$ . a model with gauge group $S U (2)_{L} \times S U (2)_{R} \times U (1)$ . We allow the gauge coupling constants of $S U (2)_{L}$ and $S U (2)_{R}$ to be different. The spontaneous symmetry breaking is accomplished only by doublets and/or singlets of $S U (2)_{L}$ and $S U (2)_{R}$ . 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 $Z b b ˉ$ vertex in the SM from the same vertex in the LRM. We effect a proper renormalization of the $Z b b ˉ$ 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 $Z b b ˉ$ vertex than a multi-Higgs extension of the SM, $v i z$ . both models can only achieve a decent fit when one admits scalar particles with very low masses $≲ 50$ GeV. This is true even when we allow for markedly different gauge coupling constants of $S U (2)_{L}$ and $S U (2)_{R}$ .

arXiv comment57 pages, 8 figures; v2: added section 3, figure 2 and three references; v3: matches published version

The Zbbˉ vertex in a left-right model

Abstract

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The $Z b b ˉ$ vertex in a left-right model