Infinite volume, three-body scattering formalisms in the presence of bound states

Abstract

Strong interactions produce a rich spectrum of resonances that decay into three or more hadrons. Understanding their phenomenology requires a theoretical framework to extract parameters from experimental data and Lattice QCD simulations of hadron scattering. Two classes of relativistic three-body approaches are currently being pursued: the EFT-based and unitarity-based one. We consider a model of relativistic three-body scattering with an 𝑆-wave bound state in the two-body sub-channel using both formalisms. We present and discuss numerical solutions for the multihadron scattering amplitudes in different kinematical regions, obtained from integral equations of the EFT-based approach. The connection of our work to the ongoing program of computing the three-body spectrum from the lattice is highlighted. Finally, we show how to generalize the unitarity-based framework to include all relevant open channels, discuss the nonphysical singularities near the physical region, and show how to eliminate them in a simple case.