Towards a discovery of BSM physics from the Cabibbo angle anomaly

TL;DR

This paper reviews recent progress in reducing Standard Model uncertainties in Cabibbo angle measurements, aiming to clarify potential signs of new physics beyond the Standard Model from observed anomalies.

Contribution

It summarizes recent theoretical and experimental developments in analyzing the Cabibbo angle anomaly and discusses future improvements to distinguish new physics from Standard Model effects.

Findings

Identification of key sources of theoretical uncertainties

Progress in refining Standard Model corrections for beta decays

Potential implications for physics beyond the Standard Model

Abstract

New developments in both the theories and experiments related to the extraction of the top-row Cabibbo-Kobayashi-Maskawa matrix elements $V_{ud}$ and $V_{us}$ led to a series of new anomalies, for instance the apparent violation of the top-row unitarity relation. It is important to further reduce all the associated Standard Model theory uncertainties in order to better understand whether such observations point towards the possibility of physics beyond the Standard Model, or rather some unexpectedly large Standard Model effects. This requires improved studies of tree-level and higher-order Standard Model corrections that enter the beta decays of pions, neutron, nuclei and kaons. We will briefly review the recent progress along this direction and discuss possible improvements in the future.