Large-scale structure of the Universe and the nature of dark matter

We use a sample of similar to 4500 Lyman-alpha absorbers to investigate their properties in the framework of a model of formation and evolution of dark matter (DM) structure elements based on the modified Zeldovich theory of gravitational instability. This model is consistent with numerical simulations of absorbers formation and emphasizes the generic similarity of the large-scale structure in the galaxy distribution and absorbers. This model allows us to estimate the column dendity and over-density of DM and gaseous matter and the entropy of the gas trapped within the DM potential wells. The obtained parameters of the DM component are consistent with theoretical expectations for the Gaussian initial perturbations with the dark matter like power spectrum. The analysis of redshift distribution of absorbers confirms the self-consistency of this model of absorbers, Gaussianity of the initial perturbations and allows one to estimate the shape of the initial power spectrum at small scales that, in turn, restricts the mass of the dominant fraction of DM particles to M(DM) greater than or equal to 1.5-5 keV.