Higgs Couplings and Precision Electroweak Data

Understand

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 2.4 sigma deviation in the forward-backward asymmetry of the bottom quark A_{FB}^b, and 2) the 2.3 sigma deviation in R_b, the ratio of the Z \rightarrow b \bar 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_{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 Z b\bar b vertex and thus correcting A_{FB}^b and R_b.