Theoretical point of view on Cabibbo angle anomaly

TL;DR

This paper discusses the Cabibbo angle anomaly, a deviation from CKM unitarity, and explores potential new physics explanations including vector-like quarks and sterile neutrinos, highlighting future experimental probes.

Contribution

It provides a theoretical analysis of the Cabibbo angle anomaly and proposes two new physics models to explain the deviation from CKM unitarity.

Findings

Identifies a 3σ deficit in first-row CKM unitarity.

Proposes heavy vector-like quark models as an explanation.

Suggests sterile neutrino models as an alternative explanation.

Abstract

We present the current situation of the determinations of the first-row CKM components and show the Cabibbo angle anomaly corresponding to a deficit in the first-row CKM unitarity condition at the $3\sigma$ level. In this contribution, we show two new physics interpretations: heavy vector-like quark models and a MeV scale sterile neutrino models. The super tau-charm facility will directly probe the other CKM unitarity conditions related to $V_{cd}$.