Parameters extraction by Planck for a CDM model with BSI steplike primordial spectrum and cosmological constant

We consider a class of spatially flat cold dark matter (CDM) models, with a cosmological constant and a broken-scale-invariant (BSI) steplike primordial spectrum of adiabatic perturbations, previously found to be in very good agreement with observations. Performing a Fisher matrix analysis, we show that some free parameters (defining the step) of our BSI model could be extracted with remarkable accuracy by the Planck satellite, thanks to the polarisation anisotropies measurements. Further, cosmological parameters could still be found with very good precision, despite a larger number of free parameters than in the simplest inflationary models.