The Z -> bb decay asymmetry and flavor changing neutral currents

TL;DR

The paper discusses a discrepancy in Z boson decay asymmetry measurements that could suggest new physics affecting third-generation quarks, with implications for rare decay rates and potential explanations involving extended gauge theories.

Contribution

It proposes that the observed asymmetry discrepancy may indicate new interactions in third-generation quarks, linking it to enhanced rare decay rates and extended gauge symmetry models.

Findings

Discrepancy in A_b parameter at 99% confidence level.

Potential for enhanced rare K and B decay rates.

Implications for extended gauge theories like SU(2)_L x SU(2)_R.

Abstract

The measured value of A_b, the Z \bar bb asymmetry parameter, disagrees with the Standard Model at 99% confidence level. If genuine the discrepancy could indicate new interactions unique to third generation quarks, implying enhanced Z penguin amplitudes. Enhanced rates are predicted for rare K and B decays, such as K^{+} --> pi^{+}\bar nu nu, K_{L} --> pi^{0}\bar nu nu, B --> X_{s}\bar nu nu, and B_{s} --> \bar mu mu. Measurements of epsilon^{\prime}/epsilon then imply QCD penguin amplitudes must also be similarly enhanced. The Higgs sector of an SU(2)_L x SU(2)_R gauge theory has some of the features needed to explain these phenomena and would also imply right-handed penguin amplitudes.