English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We discuss the issue of perturbativity in single-field inflationary modelswith a phase of ultra slow-roll (USR) tailor suited to generate an order-oneabundance of primordial black holes (PBHs). More in detail, we impose thecondition that loop corrections made up of short-wavelength modes enhanced bythe USR dynamics do not alter the tree-level power spectrum of curvatureperturbations. In our analysis, the USR phase is preceded and followed by twostages of ordinary slow-roll (SR), and we model the resulting SR/USR/SRdynamics using both instantaneous and smooth transitions. Focusing on scalesrelevant for CMB observations, we find that it is not possible, with thesearguments, to rule out the scenario of PBH formation via USR, not even in thelimit of instantaneous transition. However, we also find that loop correctionsof short modes on the power spectrum of long modes, even though not largeenough to violate perturbativity requirements, remain appreciable and, mostimportantly, are not tamed in realistic realisations of smooth SR/USR/SRtransitions. This makes perturbativity a powerful theoretical tool to constrainUSR dynamics. We extend the analysis at any scale beyond those relevant for CMBobservations. We find that loop corrections of short modes remain within thefew percent if compared to the tree-level power spectrum. However, we also findone notable exception of phenomenological relevance: we show that the so-calleddip in the power spectrum of curvature perturbation is an artifact of thetree-level computation.

One loop to rule them all: Perturbativity in the presence of ultra slow-roll dynamics