PoS - Proceedings of Science
Volume 380 - Particles and Nuclei International Conference 2021 (PANIC2021) - Flavour physics - CKM and beyond
Explaining the Cabibbo Angle Anomaly
C.A. Manzari
Full text: pdf
Pre-published on: March 28, 2022
Published on: May 24, 2022
The Cabibbo-Cobayashi-Maskawa (CKM) matrix parametrizes the misalignement between the up- and down-quark mass basis in the Standard Model (SM). The observation of first row CKM unitarity violation has recently emerged as a new anomaly of the SM, known as the "Cabibbo Angle Anomaly" (CAA). With current measurements, comparing the elements $V_{ud}$ and $V_{us}$ extracted from beta and kaon decays respectively, the tension with the SM prediction amounts to $\sim $$3\,\sigma$. Recently, it has been pointed out that this anomaly can also be seen as a discrepancy in the determination of the Fermi constant from muon decay vs $\beta$ and K decays, once CKM unitarity is assumed. In fact, possible explanations in terms on New Physics fall under two broad classes: contributions to $\beta$ decay and/or to $\mu$ decay. In this proceedings, we discuss these solutions in terms of gauge invariant dimension 6 operators in SMEFT and simplified extensions of the Standard Model. The latter could introduce correlations with other anomalies in the SM, pointing to new and interesting directions for model building.
DOI: https://doi.org/10.22323/1.380.0162
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