Unstable states in a finite volume
PD Dr. Akaki Rusetsky (Universität Bonn)

I review selected topics in the study of the properties of the unstable states on the lattice. In particular, I consider the generalization of Luescher formula for the case of multiparticle scattering by using twisted boundary conditions. It is shown that one may use this technique to investigate the position of the S-matrix poles in the pi pi and pi eta scattering near K barK threshold, which correspond to f0 and a0 mesons.
Further, I discuss the application of Luescher approach to the calculation of the resonance matrix elements. Finally, an alternative method for the extraction of a resonance energy and width is formulated and tested for the 1+1 dimensional spin model.