Probing primordial perturbations on small scales through dark matter halos

The precise measurements of small-scale primordial perturbations will be one of the main cosmological topics among the several observational missions in the future. I will discuss new approaches to probe the perturbations focusing on the standard dark matter (DM) halos and small-mass DM halos formed at higher redshift from excess power of primordial perturbations, which are sometimes called ultracompact minihalos (UCMHs). I will first show that measurements of the cosmological free-free signals in future radio observations might provide more stringent constraints on the primordial small-scale perturbations while carefully removing the Galactic free-free emission is required. Secondly, I will show the approaches regarding UCMHs. Investigations on the abundance of UCMHs lead us to know the amplitude of primordial perturbations on small scales. I will discuss the ionization effect of first-generation stars formed in UCMHs on the cosmic reionization history using the Planck CMB observation data and test the abundance of UCMHs. I will show the results to limit the abundance of UCMHs with masses larger than 10^8.4 M_solar and the constraint on the amplitude of the primordial small-scale perturbations tighter than that of previous works.