Formation and internal structure of superdense dark matter clumps and ultracompact minihaloes

Abstract

We discuss the formation mechanisms and structure of the superdensedark matter clumps (SDMC) and ultracompact minihaloes (UCMH),outlining the differences between these types of DM objects. Wedefine as SDMC the gravitationally bounded DM objectswhich have come into virial equilibrium at the radiation-dominated(RD) stage of the universe evolution. Such objects can be formed from theisocurvature (entropy) density perturbations or from the peaks in thespectrum of curvature (adiabatic) perturbation. The axionminiclusters (Kolb and Tkachev 1994) are the example of the formermodel. The system of central compact mass (e.g. in the form of SDMCor primordial black hole (PBH)) with the outer DM envelope formed inthe process of secondary accretion we refer to as UCMH. Therefore, theSDMC can serve as the seed for the UCMH in some scenarios. Recently,the SDMC and UCMH were considered in the many works,and we try to systematize them here. Weconsider also the effect of asphericity of the initial densityperturbation in the gravitational evolution, which decreases the SDMCamount and, as the result, suppresses the gamma-ray signal from DMannihilation.