Unstable particles in finite volume: The broken phase of the $4$-d $O(4)$ non-linear $\sigma$-model

Frank Zimmermann, Jörg Westphalen, Meinulf Göckeler +1

According to a proposal of Lüscher it is possible to determine elastic scattering phases in infinite volume from the energy spectrum of two-particle states in a periodic box. We de…