Towards a formalism for pion-pion scattering from staggered lattice QCD

by Dean Valois (University of Granada)

Tuesday May 12, 2026, 4:00 PM → 6:00 PM Europe/Zurich

4/2-037 - TH meeting room (CERN)

Scattering processes featuring the strong interactions can be studied using lattice QCD by means of the Lüscher formalism. This approach relies on analyticity and unitarity of the S-matrix to relate finite-volume energy levels to infinite-volume scattering amplitudes. One of the most common fermion actions in lattice QCD studies relies on staggered fermions due to their high computational efficiency. However, simulations employing staggered fermions, in addition to the fourth rooting procedure, manifest unitarity-violating effects. Moreover, the meson sector of this theory contains multiple pions as a result of the so-called taste splitting. Both of these discretization artifacts scale with the lattice spacing squared and thus disappear in the continuum. Nevertheless, at non-zero lattice spacing, unitarity violation and taste splitting hinder the applicability of the Lüscher formalism to observables computed using staggered fermions. In this talk, we will discuss two approaches to deal with the challenges of extracting scattering amplitudes from staggered lattice QCD: (1) extrapolating the energy levels, at a fixed volume, to the continuum, where the standard version of the Lüscher formalism works, and (2) generalizing the formalism to incorporate staggered lattice artifacts. In both cases, we will highlight the crucial role played by Rooted Staggered Chiral Perturbation Theory, the effective theory describing low-energy QCD with staggered fermions.