Formation of Primordial Black Holes in Inflationary Cosmology

I present two inflationary universe models in which density fluctuations with a sharp peak on a specific scale are produced. When that scale reenters the Hubble radius in the subsequent radiation-dominated era, significant amount of primordial black holes can be produced that may be identified with massive compact halo objects with mass ∼ 0.5M⊙ observed through gravitational microlensing experiments.