Constraining the early universe with ultralight primordial black holes and vice-versa

In our presentation, we focus on ultralight PBHs, not tightly constrained in the literature, produced naturally during the preheating instability in the context of single-field inflationary models. In particular, we find that the PBH production mechanism can be so efficient that PBHs subsequently dominate the content of the universe and reheating proceeds from their evaporation. Taking into account observational constraints on the PBH abundance one can constrain the energy scales at the end of inflation and at the onset of the radiation era. Vice-versa, by studying induced second order gravitational waves generated by density perturbations underlain by PBHs themselves and taking into account GW back-reaction effects one can set constraints on the initial abundance of PBHs as a function 
of their mass.