Probing de Sitter from the horizon

TL;DR

This paper explores the physics within a de Sitter static patch by analyzing horizon correlators, generalizing quasinormal spectra, and establishing a finite-temperature effective field theory with positivity constraints.

Contribution

It introduces a novel approach to probe de Sitter space using horizon correlators, extending quasinormal spectrum analysis and formulating a boundary-coupled EFT with unitarity-based positivity constraints.

Findings

Generalized quasinormal spectrum in interacting theories

Connected horizon correlators to spectral density in dS

Derived positivity constraints on EFT parameters

Abstract

In a QFT on de Sitter background, one can study correlators between fields pushed to the future and past horizons of a comoving observer. This is a neat probe of the physics in the observer's causal diamond (known as the static patch). We use this observable to give a generalization of the quasinormal spectrum in interacting theories, and to connect it to the spectral density that appears in the K\"all\'en-Lehmann expansion of dS correlators. We also introduce a finite-temperature effective field theory consisting of free bulk fields coupled to a boundary. In matching it to the low frequency expansion of correlators, we find positivity constraints on the EFT parameters following from unitarity.