Langevin description of nonequilibrium quantum fields

Gautier, Florian; Serreau, Julien

doi:10.1103/physrevd.86.125002

Cited by 32 publications

(45 citation statements)

References 71 publications

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“…They provide useful guides for further investigations, e.g., using self-consistent resummation techniques [40]. More generally, we believe the techniques developed here and in [30] are useful tools for discussing infrared effects in the expanding de Sitter space.…”

Section: Resultsmentioning

confidence: 99%

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Infrared dynamics in de Sitter space from Schwinger–Dyson equations

Gautier

Serreau

2013

Physics Letters B

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We study the two-point correlator of an O(N) scalar field with quartic self-coupling in de Sitter space. For light fields in units of the expansion rate, perturbation theory is plagued by large logarithmic terms for superhorizon momenta. We show that a proper treatment of the infinite series of self-energy insertions through the Schwinger-Dyson equations resums these infrared logarithms into power laws. We provide an exact analytical solution of the Schwinger-Dyson equations for infrared momenta when the self-energy is computed at two-loop order. Our findings encompass previously obtained results using either stochastic or Euclidean approaches. The obtained correlator exhibits a rich structure with a superposition of free-field-like power laws. We extract mass and field-strength renormalization factors from the asymptotic infrared behavior. The latter are nonperturbative in the coupling in the case of a vanishing tree-level mass.

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Section: Resultsmentioning

confidence: 99%

“…This highlights the fact that the present perturbative evaluation of the self-energy (16) is not valid in that case. One should instead employ a nonperturbative approximation scheme, such as the 1/N-expansion [40] or self-consistent 2PI techniques [25]. 13 12 Note thatM 2 > 0 ∀ N and that m 2 dyn /M 2 = N/(N + 2).…”

Section: Discussionmentioning

confidence: 99%

Infrared dynamics in de Sitter space from Schwinger–Dyson equations

Gautier

Serreau

2013

Physics Letters B

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“…In particular, they are well suited to the study of the IR properties of de Sitter correlators and are in principle applicable to other approximation schemes. Examples presently under study include 1/N corrections to the two-point function in the O(N ) model and approximations based on twoparticle-irreducible techniques [63].…”

Section: Discussionmentioning

confidence: 99%

Nonperturbative resummation of de Sitter infrared logarithms in the large-Nlimit

Serreau¹,

Renaud²

2013

Phys. Rev. D

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We study the O(N ) scalar field theory with quartic self-coupling in de Sitter space. When the field is light in units of the expansion rate, perturbative methods break down at very low momenta due to large infrared logarithmic terms. Using the nonperturbative large-N limit, we compute the four-point vertex function in the deep infrared regime. The resummation of an infinite series of perturbative (bubble) diagrams leads to a modified power law which is analogous to the generation of an anomalous dimension in critical phenomena. We discuss in detail the role of high momentum (subhorizon) modes, including the issue of renormalization, and show that they influence the dynamics of infrared (superhorizon) modes only through a constant renormalization factor. This provides an explicit example of effective decoupling between high and low energy physics in an expanding space-time.

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“…The noise ξ k (η) is Gaussian and colored with the correlation function 49) where the fluctuation kernel N is given by eqn. (3.41).…”

Section: Effective Action: Fermionic Influence Functionalmentioning

confidence: 99%

Fermionic influence on inflationary fluctuations

Boyanovsky

2016

Phys. Rev. D

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Motivated by apparent persistent large scale anomalies in the CMB we study the influence of fermionic degrees of freedom on the dynamics of inflaton fluctuations as a possible source of violations of (nearly) scale invariance on cosmological scales. We obtain the non-equilibrium effective action of an inflaton-like scalar field with Yukawa interactions (Y D,M ) to light fermionic degrees of freedom both for Dirac and Majorana fields in de Sitter space-time. The effective action leads to Langevin equations of motion for the fluctuations of the inflaton-like field, with self-energy corrections and a stochastic gaussian noise. We solve the Langevin equation in the super-Hubble limit implementing a dynamical renormalization group resummation. For a nearly massless inflaton its power spectrum of super Hubble fluctuations is enhanced, P(k; η) = (Majorana fermions, and η 0 is the renormalization scale at which the inflaton mass vanishes. The full power spectrum is shown to be renormalization group invariant. These corrections to the super-Hubble power spectrum entail a violation of scale invariance as a consequence of the coupling to the fermionic fields. The effective action is argued to be exact in a limit of large number of fermionic fields. A cancellation between the enhancement from fermionic degrees of freedom and suppression from light scalar degrees of freedom conformally coupled to gravity suggests the possibility of a finely tuned supersymmetry among these fields.

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Langevin description of nonequilibrium quantum fields

Cited by 32 publications

References 71 publications

Infrared dynamics in de Sitter space from Schwinger–Dyson equations

Infrared dynamics in de Sitter space from Schwinger–Dyson equations

Nonperturbative resummation of de Sitter infrared logarithms in the large-Nlimit

Fermionic influence on inflationary fluctuations

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