Speaker
Description
Theoretical developments over the last few years have lead to large shifts in the nuclear corrections to superallowed beta decays, albeit with enlarged uncertainties given different theoretical approaches. Nevertheless, this has lead to a shift in the value of $V_{ud}$, and a discrepancy when compared to the value implied by CKM unitarity.
On top of this, improved precision in lattice QCD calculations have revealed another discrepancy between kaon and pion semi-leptonic decays. The combination of these three can be referred as the Cabibbo angle anomalies (since in a two flavour model all three observables should determine a single parameter, the Cabibbo angle).
After summarising the current state of these issues, I will talk about new physics models that modify the coupling of the $W$ boson to quarks as a potential explanation. I will describe the results of a general analysis of all corresponding SMEFT operators, as well as of vector-like quarks, which are UV completions of these EFT scenarios, and how other constraints are important in determining the most likely explanation.
Based upon work in arXiv:2212.06862.
