Dicke superradiance, Bose-Einstein condensation of photons and spontaneous symmetry breaking

It is shown that the phenomenon of Dicke superradiance essentially occurs due to spontaneous symmetry breaking. Two generalised versions of the Dicke model are studied, and compared with a model that describes photonic Bose-Einstein condensate, which was experimentally realised sometime back. In all the models, it is seen that the occurrence of spontaneous symmetry breaking is responsible for coherent radiation emission.