Description
I will present an effective field theory (EFT) that captures the dominant late-time behavior of massless spectator fields in de Sitter space in the presence of heavy internal fields. As expected, when the mass of these internal fields is large, the leading term reproduces the infrared-divergent contributions to correlation functions obtained in the single-field description. Remarkably, even when the mass of the spectator field is below the Hubble scale, there still exists an EFT description organized in terms of leading local operators with subdominant nonlocal corrections. Crucially, this EFT describes a mixed rather than a pure state, and its four-point functions display logarithmically growing divergences at late times. In this regime, standard perturbation theory breaks down and must be reorganized. The resulting EFT is not obtained by integrating out heavy modes in the Wilsonian sense, but instead emerges from an explicit expansion of the time-evolution operator. The outcome is a local, Markovian, and generically non-unitary effective theory that resums the leading infrared behavior of the full theory to all orders. I will discuss its structure, diagrammatic interpretation, and implications for resumming loop corrections to inflationary correlators even when the heavy fields never go on shell.
