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In-in formalism for the entropy of quantum fields in curved spacetimes
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We show how to compute the purity and entanglement entropy for quantum fields in a systematic perturbative expansion. To that end, we generalize the in-in formalism to non-unitary dynamics (i.e. accounting for the presence of an environment) and to the calculation of quantum information measures, which are not observables in the usual sense. This allows us to reduce the problem to one involving standard correlation functions, and to organize their computation in a diagrammatic expansion for which we construct the corresponding Feynman rules. As an illustration, we apply the formalism to a cosmological setting inspired by the effective field theory of inflation. We find that at late times, non-linear loop corrections share the same time behavior as the linear contribution, and only yield a slight redressing of the purity. In particular, when the environment is heavy compared to the Hubble scale, the phenomenon of recoherence previously encountered is robust to the class of non-linear extensions considered. Bridging the gap between perturbative quantum field theory and open quantum systems paves the way to a better understanding of renormalization and resummation in open effective field theories. It also enables a more systematic exploration of quantum information properties in field theoretic settings.
Forward citations
Cited by 6 Pith papers
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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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Quantitative classicality in cosmological interactions during inflation
For standard slow-roll interactions, the quantum off-shell contribution to the inflationary bispectrum becomes subdominant before horizon crossing, so classical evolution with quantum initial conditions is often sufficient.
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Effective Field Theory and In-In Correlators
Matching in-in correlators between a full theory and its effective theory requires extra boundary terms in flat space, but those terms fade away in de Sitter space.
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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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An Open Effective Field Theory for light in a medium
A dissipative open EFT for photons in a medium is constructed, featuring a deformed advanced gauge symmetry and a noise constraint vμ(jμ+ξμ)=0.
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Does decoherence violate decoupling?
Tracing out a heavy field can appear to decohere a light field, but the apparent decoherence is an artifact of the chosen bipartition; the energy-based EFT projection preserves purity.
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