Cancellation of loop corrections to soft power spectrum of inflation

Inflation theory provides an explanation for the seeds of structure formation and inhomogeneities in the cosmic microwave background (CMB) through quantum fluctuations stretched to cosmological scales during inflation. Mechanisms that enhance small-scale curvature perturbations during inflation can lead to the formation of primordial black holes after horizon re-entry. Recently, some arguments have claimed that loop corrections from such enhanced small-scale fluctuations can give a scale-invariant contribution to the large-scale power spectrum and thereby spoil the inflationary prediction for the CMB. This appears to challenge the standard tree-level expectation that large-scale curvature perturbations are conserved on superhorizon scales in single-clock inflation, and has ignited discussion. In this talk, I will show that the scale-invariant contribution from the enhanced small-scale fluctuations indeed cancels, both in an explicit one-loop calculation and as a consequence of the diffeomorphism symmetry of General Relativity.

This seminar is jointly organized by the iTHEMS–ABBL Joint Astro Study Group and the Cosmology Study Group.