The influence of critical points on polariton dispersion in the band of two-particle states

The presence of critical points in the two-phonon band in conditions of the Fermi resonance on a polariton may result in a considerable polariton dispersion inside the band of two-particle states. Moreover, the polariton linewidth, conditioned by the decay into two particles, is shown to become zero near critical points; this fact holds certain promise for the determination of the positions of critical points in side the band of two-particle states.