Revisiting Zbb¯ couplings in the littlest Higgs model with T parity under current experimental constraints

Abstract

In the littlest Higgs model with $T$ parity (LHT), we revisited $Zb\overline{b}$ couplings under current experimental constraints including the LHC Higgs data and the precision electroweak data. We study the LHT effects in the branching ratio ${R}_{b}$, the forward-backward asymmetry ${A}_{FB}^{b}$ and the left- and right-handed couplings ${g}_{Lb}$, ${g}_{Rb}$. We find that the LHT effects in ${R}_{b}$ are sizable enough to be observed at future $Z$-factories (ILC, CEPC, FCC-ee) in the allowed parameter space, while these effects in ${A}_{FB}^{b}$ are weak so that it is difficult to detect at the future experiments. The LHT model provides the large correction to the left-handed coupling ${g}_{Lb}$, which can be limited by current and future experiments.