Three-pion scattering from lattice QCD

The majority of QCD states are unstable resonances that couple strongly to multi-particle channels, with a significant fraction of these coupling to asymptotic three-particle states. Lattice QCD, being a framework that incorporates all dynamical coupling non-perturbatively, provides a promising pathway toward studying the excitations of the theory. Although challenging, lattice QCD calculations of systems composed of three-hadrons are finally being performed. In this talk, I present a calculation by the Hadron Spectrum Collaboration, Phys.Rev.Lett. 126:012001 (2021), which is the first to go from the lattice QCD correlation functions to the desired infinite-volume scattering amplitudes. I review outstanding challenges to study the low-lying resonances of QCD that couple to three particles.