“School of Astronomy”
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| Paper IPM / Astronomy / 17920 |
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| Abstract: | |
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We revisit the one-loop corrections on cosmic microwave background scale perturbations induced from small-scale modes in single field models which undergo a phase of ultraslow-roll inflation. There were concerns that large loop corrections are against the notion of the decoupling of scales and that they are canceled out once the boundary terms are included in the Hamiltonian. We highlight that the nonlinear coupling between the long and short modes and the modulation of the short mode power spectrum by the long mode are the key physical reasons behind the large loop corrections. In particular, in order for the modulation by the long mode to be significant there should be a strong scale-dependent enhancement in the power spectrum of the short mode, which is the hallmark of the ultraslow-roll inflation. We highlight the important roles played by the would-be decaying mode which were not taken into account properly in recent works claiming loop cancellation. We confirm the original conclusion that loop corrections are genuine and that they can be dangerous for primordial black hole formation unless the transition to the final attractor phase is mild.
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