Higgs couplings and precision electroweak data

Abstract

In light of the discovery of a Higgs-like particle at the LHC, we revisit the status of the precision electroweak data, focusing on two discrepant observables: 1) the long-standing 2.4σ deviation in the forward-backward asymmetry of the bottom quark $A_{\mathrm{FB}}^b$, and 2) the 2.3σ deviation in R _b , the ratio of the $Z\ \to\ b\overline{b}$ partial width to the inclusive hadronic width, which is now in tension after a recent calculation including new two-loop electroweak corrections. We consider possible resolutions of these discrepancies. Taking the data at face value, the most compelling scenario is that new physics directly affects $A_{\mathrm{FB}}^b$ and R _b , bringing the prediction into accord with the measured values. We propose a modified ‘Beautiful Mirrors’ scenario which contains new vector-like quarks that mix with the b quark, modifying the $Zb\overline{b}$ vertex and thus correcting $A_{\mathrm{FB}}^b$ and R _b . We show that this scenario can lead to modifications to the production rates of the Higgs boson in certain channels, and in particular a sizable enhancement in the diphoton channel. We also describe additional collider tests of this scenario.