Primordial black holes from single-field inflation: a fine-tuning audit

Understand

All single-field inflationary models invoke varying degrees of tuning in order to account for cosmological observations.

• Mechanisms that generate primordial black holes (PBHs) from enhancement of primordial power at small scales posit inflationary potentials that transiently break scale invariance and possibly adiabaticity over a range of modes.
• This requires additional tuning on top of that required to account for observations at scales probed by cosmic microwave background (CMB) anisotropies.
• In this paper we study the parametric dependence of various single-field models of inflation that enhance power at small scales and quantify the degree to which coefficients in the model construction have to be tuned in order for certain observables to lie within specified ranges.