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The Cosmological Tree Theorem
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A number of diagrammatic "cutting rules" have recently been developed for the wavefunction of the Universe which determines cosmological correlation functions. These leverage perturbative unitarity to relate particular "discontinuities" in Feynman-Witten diagrams (with cosmological boundary conditions) to simpler diagrams, in much the same way that the Cutkosky rules relate different scattering amplitudes. In this work, we make use of a further causality condition to derive new cutting rules for Feynman-Witten diagrams. These lead to the cosmological analogue of Feynman's tree theorem for amplitudes, which can be used to systematically expand any loop diagram in terms of (momentum integrals of) tree-level diagrams. As an application of these new rules, we show that certain singularities in the wavefunction cannot appear in equal-time correlators due to a cancellation between "real" and "virtual" contributions that closely parallels the KLN theorem. Finally, when combined with the Bunch-Davies condition that certain unphysical singularities are absent, these cutting rules completely determine any tree-level exchange diagram in terms of simpler contact diagrams. Altogether, these results remove the need to ever perform nested time integrals when computing cosmological correlators.
Forward citations
Cited by 7 Pith papers
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All Tree-Level Massive Cosmological Correlators via Spectral Gluing
Tree-level massive de Sitter correlators are constructed by gluing Lauricella-type vertex functions according to graph combinatorics, and the hypergeometric content collapses to rational functions once the dynamical p...
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Propagator positivity bounds for cosmological correlators
An infinite tower of two-sided positivity bounds constrains the EFT coefficients of heavy fields on de Sitter, ruling out correlators with no unitary/causal UV completion.
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Unitarity, Recursion and Soft Limits in (EA)dS through Dressing
Structural properties of (E)AdS cosmological correlators—cutting rules, tree theorems, BCFW recursion, and soft limits—are obtained by dressing flat-space amplitudes with auxiliary propagators.
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Correlators are simpler than wavefunctions
Equal-time correlators are simpler than wavefunctions because they come from full-spacetime integrals; this implies fewer poles, cleaner factorization, and a systematic pole expansion whose first subleading term vanishes.
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Efficient training of photonic quantum generative models
Photonic quantum generative models can be trained classically via maximum mean discrepancy, with deployment corresponding to boson sampling.
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Cosmological Cutting Rules from Flat-Space Unitarity via Dressing
Flat-space Cutkosky cuts, after cosmological dressing and analytic continuation, become the Disc operations appearing in dS/EAdS cosmological cutting rules.
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EFT Perspective On de-Sitter S-Matrix
In a carefully chosen limit, the de Sitter scattering amplitude is written as an integral transform of the flat-space amplitude, and requiring energy conservation on exceptional de Sitter scalars reproduces DBI and Sp...
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