  We describe the Mott dissociation of pions and kaons within a Beth-Uhlenbeck
approach based on the PNJL model, which allows for a unified description of
bound, resonant and scattering states. Within this model we evaluate the
temperature and chemical potential dependent modification of the phase shifts
both in the pseudoscalar and scalar isovector meson channels for $N_f=2+1$
quark flavors. We show that the character change of the pseudoscalar bound
states to resonances in the continuum at the Mott transition temperature is
signaled by a jump of the phase shift at the threshold from $\pi$ to zero, in
accordance with the Levinson theorem. In particular, we demonstrate the
importance of accounting for the scattering continuum states, which ensures
that the total phase shift in each of the meson channels vanishes at high
energies, thus eliminating mesonic correlations from the thermodynamics at high
temperatures. In this way, we prove that the present approach provides a
unified description of the transition from a meson gas to a quark-gluon plasma.
We discuss the occurrence of an anomalous mode for mesons composed of quarks
with unequal masses which is particularly pronounced for $K^+$ and $\kappa^+$
states at finite densities a a possible mechanism to explain the "horn" effect
for the $K^+/\pi^+$ ratio in heavy-ion collisions.

High Energy Physics - Phenomenology;Nuclear Theory