Tree FCNC and non-unitarity of CKM matrix

TL;DR

This paper explores the implications of tree-level FCNC caused by CKM matrix non-unitarity, analyzing models like vector-like down quarks and leptophobic Z' to understand their effects on flavor physics observables.

Contribution

It introduces a step-by-step definition of CKM unitarity, proposes tests for non-unitarity, and examines specific models affecting flavor-changing neutral currents.

Findings

Non-unitarity of CKM can lead to observable FCNC signatures.

Phase angles in the unitarity triangle are altered in vector-like quark models.

Leptophobic Z' models impact B_s mixing measurements.

Abstract

We discuss possible signatures of the tree level FCNC, which results from the non-unitarity of CKM matrix. We first define the unitaity step-by-step, and possible test of the non-unitaity through the 4-value-KM parametrization. We, then, show how the phase angle of the unitary triangle would change in case of the vector-like down quark model. As another example of tree FCNC, we investigate the leptophobic $Z'$ model and its application to the recent $B_s$ mixing measurements.