Bispectrum islands: bootstrap bounds on cosmological correlators
File(s)
Published version
Author(s)
de Rham, Claudia
Jazayeri, Sadra
Tolley, Andrew J
Type
Journal Article
Abstract
Inspired by the amplitude bootstrap program, the spirit of this work is to constrain the space of consistent inflationary correlation functions—specifically, the bispectrum of curvature perturbations—using fundamental principles such as unitarity, locality, analyticity, and symmetries. To this end, we assume a setup for inflation in which de Sitter isometries are only mildly broken by the slow roll of the inflaton field, and study the bispectrum imprinted by a generic hidden sector during inflation. Assuming that the hidden sector’s contributions to primordial non-Gaussianity are dominated by the exchange of a scalar operator (which does not preclude high-spin UV completions), we derive nontrivial positivity constraints on the resulting bispectrum 𝐵(𝑘1,𝑘2,𝑘3). In particular, we show that 𝐵 must be negative in a certain region around the equilateral configuration. For instance, for isosceles triangles (with 𝑘2 =𝑘3) this region is given by 0.027 ≲𝑘3/𝑘1 ≤2. Furthermore, we demonstrate that unitarity imposes upper and lower bounds on the bispectrum shape, thereby carving out a bispectrum island where consistent shapes in our setup can reside. We complement our analysis by contemplating alternative setups where the coupling to the hidden sector is allowed to strongly break de Sitter boosts. We also identify situations that would push the bispectrum off the island and the profound physical features they would reveal.
Date Issued
2025-10-15
Date Acceptance
2025-09-16
Citation
Physical Review D: Particles, Fields, Gravitation and Cosmology, 2025, 112 (8)
ISSN
1550-7998
Publisher
American Physical Society
Journal / Book Title
Physical Review D: Particles, Fields, Gravitation and Cosmology
Volume
112
Issue
8
Copyright Statement
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3 .
License URL
Identifier
10.1103/q6rq-sj9t
Subjects
Astronomy & Astrophysics
Physical Sciences
Physics
Physics, Particles & Fields
Science & Technology
Publication Status
Published
Article Number
083531
Date Publish Online
2025-10-16