Control of multi-particle intermediate-state effects in lattice QCD calculations of long-distance weak amplitudes

Develop and validate lattice QCD methodologies that reliably control and quantify contributions from multi-particle intermediate states in long-distance components of rare weak decay amplitudes (such as K→πℓℓ, KL→μ+μ−, and Bs→μ+μ−γ). This includes establishing a consistent finite-volume formalism and systematic-error estimates so that precise Standard Model predictions for these processes can be obtained.

Background

The precision interpretation of rare and forbidden flavour-changing processes increasingly relies on first-principles lattice QCD inputs, including long-distance contributions to weak amplitudes.

Recent advances have enabled first steps toward computing these long-distance effects, but robust treatment of multi-hadron intermediate states remains a key bottleneck for achieving controlled uncertainties.

Resolving this issue is essential for making stringent Standard Model predictions that can be confronted with the high-precision measurements expected at future e+e− facilities.