Superhorizon entanglement entropy from particle decay in inflation

Abstract

In inflationary cosmology all particle states decay as a consequence of the lack of kinematic thresholds. The decay of an initial single particle state yields an \emph{entangled quantum state of the product particles}. We generalize and extend a manifestly unitary field theoretical method to obtain the time evolution of the quantum state. We consider the decay of a light scalar field with mass $M\ll H$ with a cubic coupling in de Sitter space-time. Radiative corrections feature an infrared enhancement manifest as poles in $\Delta =M^2/3H^2$ and we obtain the quantum state in an expansion in $\Delta$. To leading order in $\Delta$ the pure state density matrix describing the decay of a particle with sub-horizon wavevector is dominated by the emission of superhorizon quanta, describing \emph{entanglement between superhorizon and subhorizon fluctuations and correlations across the horizon}. Tracing over the superhorizon degrees of freedom yields a mixed state density matrix from which we obtain the entanglement entropy. Asymptotically this entropy grows with the \emph{physical} volume as a consequence of more modes of the decay products crossing the Hubble radius. A generalization to localized wave packets is provided. The cascade decay of single particle states into many particle states is discussed. We conjecture on \emph{possible} impact of these results on non-gaussianity and on the ``low multipole anomalies'' of the CMB.

discussion on wave packets and cascade decay, 18 pages, 3 figs

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• Entanglement and out-of-equilibrium dynamics in holographic models of de Sitter QFTs
• The Open Effective Field Theory of Inflation
• Cosmological Consequences of Initial State Entanglement
• Imprint of entanglement entropy in the power spectrum of inflationary fluctuations
• Information loss in effective field theory: entanglement and thermal entropies
• Loop corrections in Minkowski spacetime away from equilibrium. Part I. Late-time resummations
• Fermionic influence (action) on inflationary fluctuations
• A quantum heating as an alternative of reheating
• Superhorizon entanglement from inflationary particle production
• On the origin of entropy of gravitationally produced dark matter: the entanglement entropy
• Topological surprises in de Sitter QFT in two-dimensions
• Time evolution of cascade decay
• Entanglement negativity in de Sitter biverse from Stringy Axionic Bell pair: An analysis using Bunch-Davies vacuum