Loop corrections in the separate universe picture
Laura Iacconi, David Mulryne, David Seery

TL;DR
This paper uses the separate universe approach to analyze loop corrections in inflationary models with power spectrum spikes, clarifying back-reaction effects, scale hierarchies, and the role of long-short mode couplings.
Contribution
It introduces a novel application of the separate universe framework to compute and interpret loop corrections and back-reaction in inflationary models with hierarchical scales.
Findings
Back-reaction requires short-scale nonlinearities and long-short couplings.
In absence of long-short couplings, effects are volume-suppressed shot noise.
Explicit computations in ultra-slow-roll scenario illustrate the framework.
Abstract
In inflationary models that produce a spike of power on short scales, back-reaction of small-scale substructure onto large-scale modes is enhanced. We argue that the separate universe framework provides a highly convenient tool to compute loop corrections that quantify this back-reaction. Each loop of interest is characterized by large hierarchies in wavenumber and horizon exit time. The separate universe framework highlights important factorizations involving these hierarchies. We interpret each loop correction in terms of a simple, classical, back-reaction model, and clarify the meaning of the different volume scalings that have been reported in the literature. We argue that significant back-reaction requires both short-scale nonlinearities and long-short couplings that modulate the short-scale power spectrum. In the absence of long-short couplings, only incoherent shot noise-like…
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Taxonomy
TopicsCosmology and Gravitation Theories · Geophysics and Gravity Measurements · Galaxies: Formation, Evolution, Phenomena
