The Open Effective Field Theory of Inflation

TL;DR

This paper develops an open effective field theory framework for inflation, incorporating dissipative and non-unitary effects, to better understand primordial perturbations and their observable signatures.

Contribution

It introduces a Schwinger-Keldysh path integral approach for an open EFT of inflation, including environment interactions and derivative expansion predictions.

Findings

Predicted an enhanced bispectrum near folded configurations.

Derived power spectrum and bispectrum depend on finite effective couplings.

Matched the open EFT to explicit inflationary models.

Abstract

In our quest to understand the generation of cosmological perturbations, we face two serious obstacles: we do not have direct information about the environment experienced by primordial perturbations during inflation, and our observables are practically limited to correlators of massless fields, heavier fields and derivatives decaying exponentially in the number of e-foldings. The flexible and general framework of open systems has been developed precisely to face similar challenges. Building on previous work, we develop a Schwinger-Keldysh path integral description for an open effective field theory of inflation, describing the possibly dissipative and non-unitary evolution of the Goldstone boson of time translations interacting with an unspecified environment, under the key assumption of locality in space and time. Working in the decoupling limit, we study the linear and interacting theory in de Sitter and derive predictions for the power spectrum and bispectrum that depend on a finite number of effective couplings organised in a derivative expansion. The smoking gun of interactions with the environment is an enhanced but finite bispectrum close to the folded kinematical limit. We demonstrate the generality of our approach by matching our open effective theory to an explicit model. Our construction provides a standard model to simultaneously study phenomenological predictions as well as quantum information aspects of the inflationary dynamics.