The Roper resonance in a finite volume

Daniel Severt,Ulf-G Meißner

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