  Motivated by recent experiments with superradiant Bose-Einstein Condensate
(BEC) we consider simple microscopic models describing rigorously the
interference of the two cooperative phenomena, BEC and radiation, in
thermodynamic equilibrium. Our resuts in equilibrium confirm the presence of
the observed superradiant light scattering from BEC: (a) the equilibrium
superradiance exists only below a certain transition temperature; (b) there is
superradiance and matter-wave (BEC) enhancement due to the coherent coupling
between light and matter.
