Something about Z-penguins I want to tell

TL;DR

This paper discusses how precision measurements at LEP and SLC restrict large negative corrections to Z-penguin amplitudes in models with constrained minimal flavor violation, impacting predictions for rare K and B decays.

Contribution

It provides new stringent bounds on non-standard contributions to Z-penguin amplitudes based on LEP and SLC data, constraining flavor-changing decay predictions.

Findings

Large negative corrections to Z-penguin amplitudes are excluded by LEP/SLC data.

Derived tight limits on the Inami-Lim function C.

Predicted branching ratios for rare K and B decays are tightly constrained.

Abstract

We stress that in models with constrained minimal flavor violation large negative corrections to the flavor-changing Z-penguin amplitudes are excluded by the precision measurements of the Z -> b anti-b pseudo observables performed at LEP and SLC. The derived stringent range for the non-standard contribution to the universal Inami-Lim function C leads to tight two-sided limits for the branching ratios of all Z-penguin dominated flavor-changing K- and B-decays.