Formation of Primordial Black Holes from Warm Inflation
  Primordial Black Holes (PBHs) serve as a unique probe to the physics of the
early Universe, particularly inflation. In light of this, we study the
formation of PBHs by the collapse of overdense perturbations generated during a
model of warm inflation. For our model, we find that the primordial curvature
power spectrum is red-tilted (spectral index $n_s<1$) at the large scale (small
$k$) and is consistent with the $n_s-r$ values allowed from the CMB
observations. Along with that, it has a blue-tilt ($n_s>1$) for the small PBH
scales (large $k$), with a sufficiently large amplitude of the primordial
curvature power spectrum required to form PBHs. These features originate
because of the inflaton's coupling with the other fields during warm inflation.
We discuss the role of the inflaton dissipation to the enhancement in the
primordial power spectrum at the PBH scales. We find that for some parameter
range of our warm inflation model, PBHs with mass $\sim 10^3$ g can be formed
with significant abundance. Such tiny mass PBHs have a short lifetime $\sim
10^{-19}$ s and would have evaporated into Hawking radiation in the early
Universe. Further in this study, we discuss the evaporation constraints on the
initial mass fraction of the generated PBHs and the possibility of Planck mass
PBH relics to constitute the dark matter.
