Large-scale structure of the Universe in unstable dark matter models

We discuss the formation and evolution of the large-scale structure in unstable dark matter (UDM) models. The main feature of the models is that galaxy formation starts after decays. We found reasonable agreement with the observed picture for models with mass of decaying particles 60–90 eV and decay time (0.3–1.5)×109 yr. Galaxy formation in UDM models starts at z = 3 if products of decays are relativisitic at present or at least at z = 6–7 if the products are non-relativistic. The resemblance of the simulated galaxy distribution to the real one is essentially improved if we taken into account that: (i) galaxies were formed only from matter passed through shocks, (ii) only the first fraction of shocked matter was used to form galaxies and (iii) galaxy formation processes produced small-scale fluctuations inside superclusters. For the Harrison–Zeldovich spectrum, UDM models predict large-scale ΔT/T fluctuations, which contradict the results of the 'Relict' experiment. More steep spectra provide a possible solution for the problem.