Strong dynamics, minimal flavor and $R_b$

TL;DR

This paper examines how strong dynamics models of electroweak symmetry breaking affect Z-boson decay to bottom quarks and discusses the resulting experimental constraints, emphasizing the role of composite vector mesons and unitarity bounds.

Contribution

It provides a detailed analysis of the impact of composite vector mesons on Z decay widths and derives constraints on strong dynamics models without extended matter sectors.

Findings

Composite vector mesons mix with electroweak gauge fields.

Strong dynamics models predict observable shifts in Z→bb decay.

Unitarity bounds further restrict model parameters.

Abstract

We discuss how models of electroweak symmetry breaking based on strong dynamics lead to observable contributions to the Z-boson decay width to bbbar pairs even in the absence of any extended sector responsible for dynamical generation of the masses of the Standard Model matter fields. These contributions are due to composite vector mesons mixing with the Standard Model electroweak gauge fields and lead to stringent constraints on models of this type. Constraints from unitarity of WW-scattering are also considered.