The Open Effective Field Theory of Inflation (2404.15416v2)

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.

• The paper extends conventional inflation models by incorporating non-unitary dynamics from an interacting environmental framework.
• It employs the Schwinger-Keldysh formalism and a systematic power counting scheme to model dissipative processes in cosmological perturbations.
• Enhanced bispectrum signals, particularly in folded configurations, highlight observable implications of open system effects during inflation.

Overview of "The Open Effective Field Theory of Inflation"

The paper entitled "The Open Effective Field Theory of Inflation" presents a comprehensive framework for addressing non-unitary dynamics in the early universe, specifically during the inflationary epoch. The work elaborates on the formulation and usage of an open effective field theory (EFT) to account for interactions of cosmological perturbations with an unspecified environment. This is fundamentally distinct from conventional closed EFTs due to its focus on open systems, wherein the dynamics are possibly dissipative and non-unitary.

Key Contributions

The core achievement of this paper lies in extending the Effective Field Theory of Inflation (EFToI) to incorporate open system dynamics. This is motivated by the observation that inflationary dynamics occur in an environment whose influence is exponentially suppressed yet not entirely negligible. The authors employ the Schwinger-Keldysh formalism to capture the non-unitary evolution of the inflaton sector and its interaction with this environment.

Methodology

The authors develop their open effective field theory by:

• Schwinger-Keldysh Path Integral: Utilizing the Schwinger-Keldysh technique, which is well-suited for handling open quantum systems, the paper formalizes a path integral approach accounting for dissipative processes.
• Goldstone Bosons and Symmetry Breaking: The method involves analyzing the Goldstone boson corresponding to spontaneously broken time translations, emphasizing an assumption of locality in time and space.
• EFT Coefficients and Power Series: The effective actions are expanded in derivatives and organized according to a power counting scheme, allowing for systematic inclusion of various interactions within the model.

Empirical and Theoretical Insights

The paper offers numerical results and analytical approximations for power spectrum and bispectrum predictions, which diverge from unitary assumptions due to environmental interactions. Notably, the possible emergence of bispectrum signals, particularly in folded triangle configurations, marks a characteristic signature of interactions with the inflationary environment.

• Enhanced Bispectrum in Folded Configurations: A significant trait of this approach is the prediction of enhanced, yet finite, bispectrum close to folded limits, signifying environmental effects.
• Theoretical Constructs: Exploration of how unitarity can be preserved at a UV level while presenting an IR non-unitary description also forms an essential part of the paper’s contributions.

Implications and Future Directions

The construction posited in this paper allows for a nuanced understanding of early universe physics, suggesting that the inflationary period cannot be fully modeled using closed system dynamics alone. This open EFT approach potentially offers new avenues for studying quantum information properties in cosmology and provides observable predictions that could be examined with future data.

Future developments might include extending the framework to more general non-local environments and exploring its applicability in effective field theories beyond inflation. Additionally, further work is needed to understand the reduction to semiclassical limits and possible connections with stochastic Inflationary models.

Conclusively, this work represents a pivotal step towards integrating open quantum systems into the canonical model of inflation, proposing a rich interplay between quantum cosmological dynamics and observational cosmology.