Step-like discontinuities in Bose-Einstein condensates and Hawking radiation: the hydrodynamic limit

We present a detailed analytical analysis of the propagation of Bogoliubov phonons on top of Bose-Einstein condensates with spatial and temporal step-like discontinuities in the hydrodynamic limit and focus on some features in the correlations patterns, in particular of density-density correlations. The application to the study of the Hawking signal in the formation of acoustic black hole-like configurations is also discussed.