Primordial black hole (PBH) abundance limits constrain the primordial power spectrum, and hence models of inflation, on scales far smaller than those probed by cosmological observations. Single field inflation models compatible with all cosmological data can have large enough perturbations on small scales to overproduce PBHs, and hence be excluded. The standard formulas for the amplitude of perturbations do not hold for modes that exit the horizon close to the end of inflation however. We use a modified flow analysis to identify models where the amplitude of perturbations on small scales is large. For these models we carry out a numerical evolution of the perturbations and use PBH constraints to eliminate models which overproduce PBHs. We demonstrate that PBHs strongly constrain models of inflation and show that a numerical evaluation of the power spectrum decreases the number of otherwise viable models.
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