First complete calculation of how rare kaon decays happen

Physicists computed from first principles how kaons decay into leptons and antineutrinos, calculating all four structure-dependent form factors that govern these rare processes. The lattice QCD approach simulates quarks and gluons on a discrete spacetime grid, accounting for quantum fluctuations and using three different grid spacings to reach the continuum limit. These results give the Standard Model's most precise predictions for four kaon decay channels, allowing experimentalists to spot deviations that could hint at physics beyond the Standard Model.