Propagator positivity bounds for cosmological correlators

TL;DR

This paper derives an infinite set of positivity bounds on effective field theory coefficients for heavy field propagators in de Sitter space, constraining models of inflation and primordial non-Gaussianity.

Contribution

It introduces a novel set of two-sided positivity bounds applicable to cosmological correlators, linking fundamental principles to inflationary EFT constraints.

Findings

Positivity bounds restrict EFT parameters for inflationary models.

Constraints on primordial non-Gaussianity from heavy scalar exchanges.

Implications for cosmological collider signals and their shapes.

Abstract

Using unitarity and causality, we derive an infinite tower of two-sided positivity bounds on the effective field theory coefficients which describe the propagation of heavy fields on de Sitter spacetime. We design this EFT to describe propagators with the in-in boundary conditions that are relevant for cosmological correlators. Our positivity bounds therefore identify EFT correlators that can never emerge from a consistent underlying model of inflation. This implies non-trivial constraints on primordial non-Gaussianity; for instance the cosmological collider oscillations in the squeezed bispectrum from the exchange of a heavy scalar are tied to the shape of its EFT background.