  We consider a quantum theory of elastic light scattering from macroscopic
atomic sample existing in the Bose-Einstein condensate (BEC) phase. Following
to the second quantized formalism we introduce a set of coupled and closed
diagram equations for the polariton propagator contributing to the $T$ -matrix
and scattering amplitude. Our approach allows to follow important density
correction to the quasi-energy structure caused by static interaction and
radiation losses associated with incoherent scattering in the case of near
resonance excitation.
