CMB and large‐scale structure as a test of mixed models with n > 1

We compute cosmic background radiation (CBR) anisotropies in mixed models with different hot components, including neutrinos or volatile hot dark matter (HDM). The latter arises from heavier particles decaying well before matter‐‐radiation equivalence (lifetime ∼ 10 4 ‐‐10 7 s). The CBR power spectra of these models exhibit a higher Doppler peak than cold dark matter (CDM), and the discrepancy is even stronger in volatile models, both because the decay also gives rise to a neutral scalar, and because they allow quite a late derelativization of HDM, even for large Ο h . CBR experiments, together with large‐scale structure (LSS) data, are then used to constrain the space parameter of mixed models, when values of the primeval spectral index n > 1 are also considered. Even if n>1 is allowed, however, LSS alone prescribes that Ο h 90.30. LSS can be fitted by taking simultaneously a low derelativization redshift z der (down to ≃600, as is allowed in volatile models) and a high n , while CBR data from balloon‐borne experiments cause a severe selection on this part of the parameter space. In fact, late derelativization and n >1 have opposite effects on the fluctuation spectrum P ( k ), while, in contrast, they sum their action on the angular spectrum C l . Hence, unless we assume a suitable reionization, n 01.3 seems excluded by balloon‐borne experiment outputs, while a good fit of almost all CBR and LSS data is found for Ω h values between 0.11 and 0.16, n ∼1.1 and z der ∼2000‐‐5000. A smaller n is allowed, but z der should never be smaller than ≃1200.