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The Cosmological Bootstrap: Inflationary Correlators from Symmetries and Singularities

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33 Pith papers citing it
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abstract

Scattering amplitudes at weak coupling are highly constrained by Lorentz invariance, locality and unitarity, and depend on model details only through coupling constants and particle content. In this paper, we develop an understanding of inflationary correlators which parallels that of flat-space scattering amplitudes. Specifically, we study slow-roll inflation with weak couplings to extra massive particles, for which all correlators are controlled by an approximate conformal symmetry on the boundary of the spacetime. After classifying all possible contact terms in de Sitter space, we derive an analytic expression for the four-point function of conformally coupled scalars mediated by the tree-level exchange of massive scalars. Conformal symmetry implies that the correlator satisfies a pair of differential equations with respect to spatial momenta, encoding bulk time evolution in purely boundary terms. The absence of unphysical singularities completely fixes this correlator. A spin-raising operator relates it to the correlators associated with the exchange of particles with spin, while weight-shifting operators map it to the four-point function of massless scalars. We explain how these de Sitter four-point functions can be perturbed to obtain inflationary three-point functions. We reproduce many classic results in the literature and provide a complete classification of all inflationary three- and four-point functions arising from weakly broken conformal symmetry. The inflationary bispectrum associated with the exchange of particles with arbitrary spin is completely characterized by the soft limit of the simplest scalar-exchange four-point function of conformally coupled scalars and a series of contact terms. Finally, we demonstrate that the inflationary correlators contain flat-space scattering amplitudes via a suitable analytic continuation of the external momenta.

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Kontorovich-Lebedev-Fourier Space for de Sitter Correlators

hep-th · 2026-04-16 · unverdicted · novelty 8.0

A Kontorovich-Lebedev-Fourier space is built for (d+1)-dimensional de Sitter correlators from the Casimir operator of SO(1,d+1), producing rational propagators and Feynman rules that turn tree and loop diagrams into spectral integrals and orthogonality relations.

Cosmological Correlators in KLF and the Double-Exchange

hep-th · 2026-07-06 · conditional · novelty 7.0

The double-exchange cosmological correlator is computed in KLF space, yielding a double series over hypergeometric functions that improves on prior four-layer representations.

Laplace Space for Cosmological Correlators

hep-th · 2026-06-25 · unverdicted · novelty 7.0

Laplace transform converts cosmological correlator diagrams into flat-space integrals against kernels, yielding a closed-form rapidly convergent series for the massive single-exchange case valid across the full kinematic domain.

On the amplitude expansion of gluon correlators in $\textrm{AdS}_4$

hep-th · 2026-06-22 · unverdicted · novelty 7.0

Tree-level gluon correlators in AdS4 decompose into energy poles with residues given by flat-space amplitudes, curvature corrections captured by lower-point amplitudes with merged data via AdS Berends-Giele currents.

Cosmological Weight-Shifting Matrices

hep-th · 2026-05-28 · unverdicted · novelty 7.0

Introduces weight-shifting matrices for de Sitter diagrams, generalized with Kronecker products to arbitrary tree-level graphs, to derive massless wavefunction coefficients from conformally coupled seeds.

Cosmological Collider in the Grassmannian

hep-th · 2026-05-20 · unverdicted · novelty 7.0 · 2 refs

Four-point wavefunction coefficients for external conformally coupled scalars exchanging a particle of generic mass and spin are expressed in closed form as hypergeometric functions of Mandelstam invariants times Legendre polynomials in the cosmological Grassmannian.

On the simplicity of de Sitter correlators

hep-th · 2026-04-29 · unverdicted · novelty 7.0

De Sitter correlators in conformally coupled φ³ theory admit a time-integral representation built from flat-space correlators, revealing intrinsic simplifications including vanishing of odd conjugate-momentum graphs and a smaller symbol alphabet than the corresponding wavefunction coefficients.

Differential Equations for Massive Correlators

hep-th · 2026-04-09 · unverdicted · novelty 7.0

A graph-tubing combinatorial framework governs the first-order differential equations obeyed by master integrals for massive cosmological correlators in de Sitter space.

Strongly Coupled Sectors in Inflation: Gapped Theories of Unparticles

hep-th · 2025-12-29 · unverdicted · novelty 7.0

Compactified 5D unparticle theories generate gapped excitations whose exchange in inflationary correlators yields oscillations modulated by anomalous dimensions and possible interference patterns under brane-localized interactions.

Medicine show: A Calogero model with principal series states

hep-th · 2025-07-23 · unverdicted · novelty 7.0

A deformed Calogero model accommodates unitary principal series states of sl(2,R) via operator domain changes, preserving unitarity and invariance while altering integrability, with solutions for N=2 and 3.

Strongly Coupled Sectors in Inflation: Gapless Theories and Unparticles

hep-th · 2025-03-22 · unverdicted · novelty 7.0

Computes inflationary bispectra and trispectra from tree-level unparticle exchanges using Mellin-Barnes methods and symmetry-based differential equations, revealing that full shapes are needed to distinguish unparticles from light particles.

On Cosmological Correlators with Boundary Contributions

gr-qc · 2026-06-04 · unverdicted · novelty 6.0

The paper derives a correspondence between boundary terms and field redefinitions for cosmological correlators and classifies non-vanishing boundary contributions in massive-exchange diagrams under dS isometries and broken boosts.

Cosmological Collider Signatures from Right-Handed Neutrino Loop

hep-ph · 2026-05-20 · unverdicted · novelty 6.0

Right-handed neutrino loops in inflation with seesaw mechanism generate enhanced cosmological collider signatures via a chemical potential from a dimension-5 operator, softening Boltzmann suppression and amplifying oscillatory non-Gaussianity for the dominant helicity mode.

Non-Relativistic Cosmological Collider Signals

hep-ph · 2026-05-19 · unverdicted · novelty 6.0

Non-relativistic propagation of a tilted-ghost spectator field during inflation produces boostless cosmological collider non-Gaussianity via an effective chemical-potential-like tilt parameter.

Kinematic Flow for Banana Loops and Unparticles

hep-th · 2026-04-24 · unverdicted · novelty 6.0

Banana loop cosmological correlators are captured by master integrals from tubings of marked graphs, with connection matrices derived from activation, merger, swap, and copy rules unique to unparticle exchanges.

Massive Exchange and the Sign of the Equilateral Bispectrum

hep-th · 2026-04-07 · unverdicted · novelty 6.0

The equilateral bispectrum from massive scalar exchange in inflation is not universally negative in the full EFT of inflation; its sign depends on a critical ratio of operator coefficients.

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