Parameter extraction by Planck for a cold dark matter model with broken scale invariance 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) step-like primordial spectrum of adiabatic perturbations, previously found to be in very good agreement with observations. Performing a Fisher matrix analysis, we show that, in the case of a large gravitational wave (GW) contribution, some free parameters (defining the step) of our BSI model can be extracted with remarkable accuracy by the Planck satellite, thanks to the polarization anisotropy measurements. Further, cosmological parameters can still be found with very good precision, despite a larger number of free parameters than in the simplest inflationary models.