Mixed models with n>1 and large-scale structure constraints

Recent data on CBR anisotropies show a Doppler peak higher than expected in CDM cosmological models, if the spectral index n = 1. However, CDM and LCDM models with n > 1 can hardly be consistent with LSS data. Mixed models, instead, whose transfer function is naturally steeper because of free-streaming in the hot component, may become consistent with data if n > 1, when Omega(h) is large. This is confirmed by our detailed analysis, extended both to models with a hot component whose momentum space distribution had a thermal origin (like massive neutrinos), and to models with a non-cold component arising from heavier particle decay. In this work we systematically search models which fulfill all constraints which can be implemented at the linear level. We find that a stringent linear constraint arises from fitting the extra-power parameter Gamma. Other significant constraints arise comparing the expected abundances of galaxy clusters and high-z systems with observational data. If low values of Gamma are permitted, mixed models with 1 less than or equal to n less than or equal to 1.4 can have up to similar to 45% of non-cold component, without violating any further linear constraint. Keeping to models with Gamma greater than or equal to 0.13, a suitable part of the space parameter still allows up to similar to 30% of hot component (it is worth outlining that our stringent criteria allow only models with 0.10 less than or similar to Omega(h) less than or similar to 0.16, if n less than or equal to 1). Spectra with n.1 are briefly discussed within the frame of inflationary theories. We also outline that models with such large non-cold component would ease the solution of the so-called baryon catastrophe in galaxy clusters. (C) 1998 Elsevier Science B.V. All rights reserved.