High Energy / Nuclear Theory / RIKEN seminars

[NT/RIKEN seminar] The quest for explaining the top-row CKM unitarity deficit

by Chien Yeah Seng


Symmetries of the weak sector of the Standard Model and its completeness find an exact mathematical realization in the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix. Of various relations among its elements, the top-row unitarity relation is by far the one known with the highest precision.
The last few years have seen a rapid development in both the theory and experiments related to the extraction of the top-row CKM matrix elements and the respective unitarity relation, as quoted in the 2020 PDG: 


The apparent 3sigma deviation from unitarity points towards the possibility of BSM physics. Therefore, it is important to further reduce all the SM uncertainties in both V_{ud} and V_{us} in order to reach a level sufficient to claim a discovery. This involves a better understanding of various QCD matrix elements that enter the beta decays of neutron, nuclei and kaon, in particular those governing the electromagnetic radiative corrections (EMRC) in such processes. In this talk I will briefly describe the recent progress along this direction and discuss possible improvements in the future.