Leptophilic New Physics and the Cabibbo Angle Anomaly

TL;DR

This paper explores leptophilic extensions of the Standard Model to explain the Cabibbo Angle Anomaly, analyzing how new particles like vectorlike leptons, scalar singlets, or Z' bosons impact CKM unitarity and the determination of V_{ud}.

Contribution

It introduces simplified leptophilic models that modify the Fermi constant and CKM element measurements, providing new insights into the anomaly.

Findings

Leptophilic models can account for the CKM unitarity deficit.

New contributions to the Fermi constant are significant in these models.

The models suggest potential signals for future experimental tests.

Abstract

The Cabibbo Angle Anomaly, an apparent deficit in first-row CKM unitarity, can be addressed by leptophilic Standard Model extensions that generate new contributions to the Fermi constant and affect the determination of the CKM element $V_{ud}$. We focus on simplified models with this property, including the Standard Model extended by vectorlike leptons, by the singly charged scalar singlet, or by a leptophilic $Z'$ boson.