Two-Body Transition Amplitudes: A Pathway to Resonant Form-Factors

Understanding the structure of hadronic resonant states has proven difficult due to their short lifetimes as well as the non-perturbative nature of QCD. However, such information can be extracted from a class of scattering amplitudes that couple two-body states via a single external current. In this talk, I will present an exact analytic representation for the on-shell amplitudes in terms of generalized form-factors and known kinematic functions. From these amplitudes, I will then show how to define the elastic form-factors of resonant states. The finite-volume formalism presented in [Phys. Rev. D 100, 034511] allowed for the extraction of these amplitudes from lattice QCD. Combined with this formalism, this work provides a comprehensive foundation for calculating resonant from-factors using lattice techniques.