A new theory framework for the electroweak radiative corrections in Kl3 decays

Chien-Yeah Seng, Daniel Galviz, Ulf-G. Meißner
2020 Journal of High Energy Physics  
We propose a new theory framework to study the electroweak radiative corrections in K l3 decays by combining the classic current algebra approach with the modern effective field theory. Under this framework, the most important O(G F α) radiative corrections are described by a single tensor T µν involving the time-ordered product between the charged weak current and the electromagnetic current, and all remaining pieces are calculable order-by-order in Chiral Perturbation Theory. We further point
more » ... y. We further point out a special advantage in the K 0 l3 channel that it suffers the least impact from the poorly-constrained low-energy constants. This finding may serve as a basis for a more precise extraction of the matrix element V us in the future. K l2 : |V us | = 0.2253(7) K l3 : |V us | = 0.2231(8). (1.4) This seemingly small difference, however, makes a huge impact on ∆ CKM when combined with the updated determination of |V ud | in ref. [7]: K l2 : ∆ CKM = −0.0012(4) K l3 : ∆ CKM = −0.0022(5). (1.5) The first line in this equation exhibits an interesting hint for possible BSM physics, but might be loosened after accounting for possible missing nuclear effects in the V ud extraction. The second line, on the other hand, represents almost a confirmed signal. Furthermore, a recent lattice study of the Kπ form factor at zero momentum transfer improves the K l3 -extraction: |V us | = 0.22333(61), leading to ∆ CKM = −0.0021(4), a 5σ violation of
doi:10.1007/jhep02(2020)069 fatcat:oppa6fz7fbb6pcj53qilujrvtm