Solving the A{FB}^b anomaly in natural composite models

TL;DR

This paper explores natural composite Higgs models to address the AFB^b anomaly, ensuring compatibility with electroweak precision tests and predicting new fermionic resonances.

Contribution

It identifies the role of custodial symmetry in solving the AFB^b anomaly within composite Higgs models, detailing the embedding of operators and parameter space constraints.

Findings

Successful reproduction of Rb, top, and bottom masses

Predictions for light fermionic resonance spectrum

Corrections to Zt anti-t couplings

Abstract

The Standard Model with a light Higgs provides a very accurate description of the electroweak precision observables. The largest deviation between the Standard Model predictions and the experimental measurements, the forward-backward asymmetry of the bottom quark A{FB}^b, can be interpreted as an indication of new physics at the TeV scale. The strong agreement between theory and experiment in the branching fraction of the Z into b-quarks puts strong constraints for new physics aiming to solve the A{FB}^b puzzle. We study a class of natural composite Higgs models that can solve the A{FB}^b anomaly reproducing the observed Rb as well as the top and bottom masses. We find that the subgroup of the custodial symmetry able to protect Zb_L anti-b_L from large corrections generated by the top sector play an important role if we want to maintain naturalness in the composite sector. We make a thorough study of the composite operators mixing with the b-quark, determine their embedding under the global composite symmetry and the parameter space that lead to the correct Zb anti-b couplings while keeping the top and bottom masses to their physical values. We study the predictions for the spectrum of light fermionic resonances and the corrections to Zt anti-t couplings in this scenario.