Evidence for an inflationary phase transition from the LSS and CMB anisotropy data

In the light of the recent Boomerang and Maxima observations of the CMB whi ch show an anomalously low second acoustic peak, we reexamine the predictio n by Adams et al (1997) that this would be the consequence of a 'step' in t he primordial spectrum induced by a spontaneous symmetry breaking phase tra nsition during primordial inflation. We demonstrate that a deviation from s cale-invariance around k similar to 0.1 h Mpc(-1) can simultaneously explai n both the feature identified earlier in the APM galaxy power spectrum as w ell the recent CMB anisotropy data, with a baryon density consistent with t he BBN value. Such a break also allows a good fit to the data on cluster ab undances even for a critical density matter-dominated universe with sere co smological constant.