Physics

In the last two decades, unexpected exotic resonances discovered in experiments challenged the quark model lore of hadrons. Tetraquarks, pentaquarks, molecules, hybrids, and glueball candidates sprung forth and revitalized the field of hadron spectroscopy. Many of those intriguing states decay into three or more particles. Due to non-trivial three-body couplings, determining their masses and widths requires some of the most complicated techniques on the border between lattice QCD and scattering theory. During the talk, I will review recent formal developments in this field, focusing on the importance of the analytic properties of the on-shell three-particle amplitudes. As an example, results from the studies of Efimov states, doubly-charmed tetraquark T_cc, and mixed systems of light mesons will be presented.