Inflaton Clusters and Inflaton Stars
  In a broad class of scenarios, inflation is followed by an extended era of
matter-dominated expansion during which the inflaton condensate is
nonrelativistic on subhorizon scales. During this phase density perturbations
grow to the point of nonlinearity and collapse into bound structures. This
epoch strongly resembles structure formation with ultra-light axion-like
particles. This parallel permits us to adapt results from studies of
cosmological structure formation to describe the nonlinear dynamics of this
post-inflationary epoch. We show that the inflaton condensate fragments into
"inflaton clusters", analogues of axion dark matter halos in present-day
cosmology. Moreover, solitonic objects or "inflaton stars" can form inside
these clusters, leading to density contrasts as large as $10^6$ in the
post-inflationary universe.
