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De Sitter Diagrammar and the Resummation of Time
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Light scalars in inflationary spacetimes suffer from logarithmic infrared divergences at every order in perturbation theory. This corresponds to the scalar field values in different Hubble patches undergoing a random walk of quantum fluctuations, leading to a simple toy "landscape" on superhorizon scales, in which we can explore questions relevant to eternal inflation. However, for a sufficiently long period of inflation, the infrared divergences appear to spoil computability. Some form of renormalization group approach is thus motivated to resum the log divergences of conformal time. Such a resummation may provide insight into De Sitter holography. We present here a novel diagrammatic analysis of these infrared divergences and their resummation. Basic graph theory observations and momentum power counting for the in-in propagators allow a simple and insightful determination of the leading-log contributions. One thus sees diagrammatically how the superhorizon sector consists of a semiclassical theory with quantum noise evolved by a first-order, interacting classical equation of motion. This rigorously leads to the "Stochastic Inflation" ansatz developed by Starobinsky to cure the scalar infrared pathology nonperturbatively. Our approach is a controlled approximation of the underlying quantum field theory and is systematically improvable.
Forward citations
Cited by 7 Pith papers
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On Cosmological Correlators at One Loop
The one-loop triangle in-in correlator of massless scalars in flat space is evaluated in closed form in terms of dilogarithms, with Landau analysis revealing its physical singularities and a partial-energy factorisati...
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Stochastic inflation from a non-equilibrium renormalization group
Stochastic inflation is the leading infrared limit of a coarse-grained Schwinger–Keldysh effective theory, and the same Fokker–Planck dynamics follows from a Polchinski-type renormalization-group flow for the reduced ...
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Confronting infrared divergences in de Sitter: loops, logarithms and the stochastic formalism
The authors show that loop corrections do not alter tree-level time dependence in de Sitter correlators, so secular growth is a regularization artifact, not a physical effect.
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Renormalisation and matching of massless scalar correlation functions in Soft de Sitter Effective Theory
SdSET is shown to renormalise and match like a flat-space EFT: tree-level trispectrum and six-point matching plus a one-loop power-spectrum match determine the SdSET couplings and initial-condition functions.
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Inflationary Decoherence from the Gravitational Floor
Gravitational self-interactions alone decohere super-Hubble inflationary fluctuations with purity loss growing as (aH/k)^5, faster than the a^3 growth of earlier calculations.
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Stochastic inflation as an open quantum system
Stochastic inflation emerges from an open-quantum-system derivation, with a Lindblad master equation that reduces to and corrects Starobinsky's Fokker-Planck equation.
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The Quantum Mechanics of Rare Events: From Quantum Walks to Stochastic Inflation
Rare fluctuations in quantum walks are ruled by a measurement-induced relative entropy, and applying this to stochastic inflation yields a steady state that violates detailed balance.
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