Alla Bezvershenko
We develop an approach to describe the Dicke transition of interacting many-particle systems strongly coupled to the light of a lossy cavity. A mean-field approach is combined with a perturbative treatment of fluctuations beyond mean-field, which becomes exact in the thermodynamic limit. Fluctuations are crucial to determine the mixed state character of the transition and to unravel universal properties of the emerging self-organized states. A rate equation is used to calculate an effective temperature. We validate our results by comparing to time-dependent matrix-product-state calculations.