Flavour universality of the $W^\pm$ and $Z$ fermionic couplings

TL;DR

This paper reviews empirical evidence supporting the universality of fermionic couplings to the $W^$ and $Z$ gauge bosons, highlighting the Standard Model's replication of fermion families and the experimental tests of their coupling strengths.

Contribution

It provides a comprehensive overview of the experimental validation of fermion coupling universality in the Standard Model.

Findings

Strong experimental support for flavor universality of $W^$ and $Z$ couplings

Most precise tests confirm equal coupling strengths across fermion families

Both charged-current and neutral-current interactions exhibit universality

Abstract

The Standard Model does not provide any dynamical explanation of the existence of different families of fermions. To account for this experimental fact, it just replicates three times its single-family gauge structure. The equal-charge fermions of the different families couple to the gauge bosons with exactly the same coupling strength. We overview the empirical evidence supporting this important property. The currently most precise experimental tests on the universality of the lepton and quark couplings are discussed. Both charged-current ($W^\pm$) and neutral-current ($Z$) interactions are reviewed.