Control multi-particle intermediate-state contributions in lattice QCD calculations of second-order weak processes

Determine how to control and incorporate contributions from multi-hadron intermediate states in lattice QCD computations of long-distance second-order weak processes, including K→πℓ+ℓ−, KL→μ+μ−, and Bs→μ+μ−γ, so that precise Standard Model predictions can be provided for global flavour fits and rare-decay phenomenology.

Background

Lattice QCD enables first-principles calculations of hadronic matrix elements that enter precision flavour observables, but extending these methods to processes governed by second-order weak interactions still faces technical challenges.

In rare kaon and B-meson decays, long-distance contributions from multi-hadron intermediate states can be sizeable and must be accurately controlled to match the experimental precision anticipated at future Higgs/electroweak/top factories.

Addressing this problem will improve the reliability of theoretical inputs to global analyses of flavour observables, thereby sharpening indirect searches for physics beyond the Standard Model.