Primordial black holes from inflaton and spectator field perturbations
  in a matter-dominated era
  We study production of primordial black holes (PBHs) during an early
matter-dominated phase. As a source of perturbations, we consider either the
inflaton field with a running spectral index or a spectator field that has a
blue spectrum and thus provides a significant contribution to the PBH
production at small scales. First, we identify the region of the parameter
space where a significant fraction of the observed dark matter can be produced,
taking into account all current PBH constraints. Then, we present constraints
on the amplitude and spectral index of the spectator field as a function of the
reheating temperature. We also derive constraints on the running of the
inflaton spectral index, ${\rm d}n/{\rm d}{\rm ln}k \lesssim -0.002$, which are
comparable to those from the Planck satellite for a scenario where the
spectator field is absent.
