Ansatz for small FCNC with a non-universal $Z^\prime$

TL;DR

This paper proposes a class of models with a non-universal $Z'$ that suppresses FCNC in the down-quark sector, reducing experimental constraints and predicting the largest FCNC in the $tc$ transition.

Contribution

It introduces a specific down-quark mass matrix structure that naturally suppresses FCNC in the down sector while allowing potentially observable effects in the top-charm transition.

Findings

FCNC in the down-quark sector are suppressed or vanish

Largest FCNC occurs in the $tc$ transition with strength comparable to $V_{ts}$

Models are consistent with experimental constraints

Abstract

It is well known that a non-universal $Z^\prime$ induces tree-level FCNC which are severely constrained by experiment, most notably meson mixing. We point out that there is a class of models, with a down-quark mass matrix of the Georgi-Jarlskog form, in which the FCNC in the down-type quark sector vanish or are strongly suppressed. The largest FCNC in these models would occur in the $tc$ transition with a strength comparable to $V_{ts}$.