Higgs Couplings and Precision Electroweak Data

TL;DR

This paper revisits electroweak precision data post-Higgs discovery, addressing anomalies in bottom quark observables with a new vector-like quark model that also predicts altered Higgs production rates.

Contribution

It proposes a modified 'Beautiful Mirrors' model with vector-like quarks to resolve bottom quark anomalies and predicts enhanced Higgs diphoton production.

Findings

The model can reconcile A_{FB}^b and R_b discrepancies.

Predicts increased Higgs diphoton decay rate.

Suggests new collider signatures for vector-like quarks.

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 2.4 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. 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.