A class of spatially-flat models with cold dark matter ( CDM ) , a cosmological constant and a broken-scale-invariant ( BSI ) steplike primordial ( initial ) spectrum of adiabatic perturbations , generated in an exactly solvable inflationary model where the inflaton potential has a rapid change of its first derivative at some point , is confronted with existing observational data on angular fluctuations of the CMB temperature , galaxy clustering and peculiar velocities of galaxies .
If we locate the step in the initial spectrum at k \simeq 0.05 h { \mathrm { M } pc } ^ { -1 } , where some feature in the spectrum of Abell clusters of galaxies was found that could reflect a property of the initial spectrum , and if the large scales flat plateau of the spectrum is normalized according to the COBE data , the only remaining parameter of the spectrum is p - the ratio of amplitudes of the metric perturbations between the small scales and large scales flat plateaux .
Allowed regions in the plane of parameters ( \Omega = 1 - \Omega _ { \Lambda } , H _ { 0 } ) satisfying all data have been found for p lying in the region ( 0.8-1.7 ) .
Especially good agreement of the form of the present power spectrum in this model with the form of the cluster power spectrum is obtained for the inverted step ( p < 1 , p = 0.7 - 0.8 ) , when the initial spectrum has slightly more power on small scales .