Influence of quark boundary conditions on the pion mass in finite volume
  We calculate the mass shift for the pion in a finite volume with renormalization group (RG) methods in the framework of the quark-mesons model. In particular, we investigate the importance of the quark effects on the pion mass. As in lattice gauge theory, the choice of quark boundary conditions has a noticeable effect on the pion mass shift in small volumes, in addition to the shift due to pion interactions. We compare our results to chiral perturbation theory calculations and find differences due to the fact that chiral perturbation theory only considers pion effects in the finite volume. 
J. Braun (1), B. Klein (2), H.J. Pirner (1 and 3) ((1) Institute for   Theoretical Physics, University of Heidelberg, (2) GS...