Pion dissociation and Levinson's theorem in hot PNJL quark matter
  Pion dissociation by the Mott effect in quark plasma is described within the generalized Beth-Uhlenbeck approach on the basis of the PNJL model which allows for a unified description of bound, resonant and scattering states. As a first approximation, we utilize the Breit-Wigner ansatz for the spectral function and clarify its relation to the complex mass pole solution of the pion Bethe-Salpeter equation. Application of the Levinson theorem proves that describing the pion Mott dissociation solely by means of spectral broadening of the pion bound state beyond T_Mott leaves out a significant aspect. Thus we acknowledge the importance of the continuum of scattering states and show its role for the thermodynamics of pion dissociation. 
A. Wergieluk, D. Blaschke, Yu. L. Kalinovsky, A. Friesen
nucl-th hep-ph