Speaker
Description
In the early days of QCD phenomenology, resonances were thought to arise from single-particle constituent-quark-model-like states dressed by their decay channels to become short-lived resonances. The lowest lying resonances were of primary importance and sophisticated models were developed to accommodate them. Here the N*(1440) Roper resonance, its partner the Δ(1600) resonance and the Λ(1405) all captured the attention of model builders. However, through the consideration of coupled-channel scattering, it is well known that resonances can also arise through nonperturbative rescattering processes without any resort to a quark-model-like state. Remarkably, experimental data alone is unable to resolve these two very different interpretations of the physical structure of baryon resonances.
The important development that is enabling the resolution of resonance structure is the ability to bring the coupled-channel analysis of experimental scattering data to the finite-volume of lattice QCD where predictions can be confronted with lattice-QCD calculations. This combination of experiment and lattice QCD demands that we reevaluate our notions of baryon resonance structure.
In this presentation, the infinite-volume world of experiment and the finite-volume world of lattice QCD are bridged by Hamiltonian effective field theory (HEFT), a nonperturbative extension of effective field theory incorporating the Luescher formalism. We'll discuss the model (in)dependence of the HEFT approach and then apply it to the Nucleon, Delta and Lambda spectra with an emphasis on resolving the physical structure of these spectra. New results for the Δ(1600) and Λ(1670) will be highlighted. We'll confront state of the art lattice QCD calculations of low-lying scattering states in these channels and examine the extent to which these lattice calculations are in accord with experiment. Finally, the impact these findings have on the missing baryon resonances problem will be summarised.
