Abstract

Our understanding of the universe between the end of inflation and production of light elements is incomplete. How did inflation end? What did the universe look like at the end of inflation? In this talk, I will discuss the different scenarios of particle production at the end of inflation ((p)reheating). I will concentrate on a particular scenario: the fragmentation of the inflaton into localized, long-lived excitations of the inflaton field (oscillons), which end up dominating the energy density of the universe (if couplings to other fields are weak). Oscillons are produced in a large class of inflationary models which are theoretically well motivated and observationally consistent with the cosmic microwave background anisotropies. I will discuss conditions for their existence, emergence and stability and also report on what we have learnt about the fragmentation process from lattice simulations. Finally, I will briefly discuss possible consequences of oscillons in the early universe including a delay in radiation domination.