The Roper resonance in a finite volume

Daniel Severt,Ulf-G Meißner

Figure 2. Energy levels for various box sizes L, considering only pion and nucleon as intermediate states. Red solid lines display the numerical results, and blue dashed lines the free energy levels of the pion and nucleon for $| \vec{n}{| }^{2}=1,2,3,4$ (lowest to highest curve).