Peng-Xiang Ma, Xu Feng, Mikhail Gorchtein, Lu-Chang Jin, Keh-Fei Liu, Chien-Yeah Seng, Bi-Geng Wang, and Zhao-Long Zhang, Lattice QCD Calculation of Electroweak Box Contributions to Superallowed Nuclear and Neutron Beta Decays, Phys. Rev. Lett. 132, 191901 – Published 8 May 2024

We perform, for the first time, lattice QCD calculation of the universal axial γW-box contribution to both superallowed nuclear and neutron beta decays. In this calcualtion, we incorporate long-distance contributions to the hadronic function using the infinite-volume reconstruction method. Our results yield a higher value of  ∣V_ud∣, reducing the previous 2.1σ tension with the CKM unitarity to 1.8σ.