The 43rd International Symposium on Lattice Field Theory (Lattice 2026)

Feynman-Hellmann determination of $K\to\pi$ transition matrix elements

Not scheduled

20m

University of Maryland, College Park

Poster presentation Quark and lepton flavor physics

Speaker

Mischa Batelaan (Adelaide University)

Description

We present a lattice QCD calculation of the $K\to\pi$ vector-current matrix element using a flavour-changing Feynman-Hellmann approach, extending the transition-matrix-element formalism developed for baryons to the meson sector.
A flavour-changing temporal vector current added to the action mixes the $K$ and $\pi$ interpolating fields, and the matrix element $\langle K|V_4|\pi\rangle$ is read from the induced avoided level crossing rather than from an explicit three-point function.
We develop a generalized eigenvalue analysis using pseudoscalar and temporal-axial interpolators that disentangles the forward-propagating states and extracts the resulting shifts in their energies.
We discuss the implications for $f_+(0)$ and $|V_{us}|$.