Vector-like quark interpretation of excess in Higgs signal strength

There is a +2σ deviation in the average Higgs-signal strength for all the 7+8+13 TeV data up to Summer 2018. We find that a slight reduction of the bottom-Yukawa coupling can fit the data better than the standard model. We suggest an extension with a vector-like quark doublet, of which the right-handed component of b′ mixes nonnegligibly with the standard model b quark. We show that the mixing would induce a reduction of the bottom Yukawa coupling. Simultaneously, the coupling of the Z boson to the right-handed b quark increases, which could reduce the forward-backward asymmetry of bottom production at LEP and bring it closer to the experimental value. However, such a mixing is in tension with the ratio Rb of the partial width Z→bb¯ to the total hadronic width, and with the total hadronic width of the Z boson.