Effective field theory during inflation: Reduced density matrix and its quantum master equation

Boyanovsky, D.

doi:10.1103/physrevd.92.023527

Cited by 97 publications

(137 citation statements)

References 101 publications

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“…It is noteworthy that in contrast with the scalar field case where the corrections lead to a suppression of the amplitude as discussed in refs. [43,44], the fermionic case yields a growth of the amplitude when the wavelength of the perturbation becomes super-Hubble. This important difference is traced back to the fermionic loop in the self-energy in contrast with the bosonic loop studied in refs.…”

Section: Homogeneous Solutionmentioning

confidence: 99%

“…In absence of interactions the Langevin equation (3.48) is simply the equation of motion for free fields, its solution is more conveniently written in terms of the real growing and decaying modes as (see refs. [43,44] for details),…”

Section: Effective Action: Fermionic Influence Functionalmentioning

confidence: 99%

“…[43,44]. The operators Q k , P − k form a canonical conjugate pair and feature the following expectation values in the initial density matrix…”

Section: Effective Action: Fermionic Influence Functionalmentioning

confidence: 99%

“…A large number of degrees of freedom in the standard model and beyond are fermionic, which motivates us to apply the methods developed in refs. [41,43,44] to the case when the inflaton is Yukawa coupled to fermionic fields, to understand how the coupling to these degrees of freedom affect the power spectrum of inflaton fluctuations. Our work differs substantially from previous studies of fermions coupled to the inflaton field in the literature [19,[45][46][47][48], which focused on fermion production, or the fermionic contribution to the effective inflaton mass or self-energy.…”

Section: Motivations and Objectivesmentioning

confidence: 99%

“…[42] in terms of local correlations of environmental degrees of freedom. More recently the non-equilibrium effective action that describes the non-equilibrium dynamics of the fluctuations of an inflaton-like scalar field coupled to nearly massless scalar fields conformally or minimally coupled to gravity was studied both from the quantum density matrix [43] as well as the influence functional [44] approaches. These two approaches are complementary, both yield the effective equations of motion for fluctuations whose solution represents a non-perturbative resummation of selfenergy diagrams, however the influence action reveals a direct connection with a stochastic description [41,44].…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Homogeneous Solutionmentioning

confidence: 99%

Section: Effective Action: Fermionic Influence Functionalmentioning

confidence: 99%

“…[43,44]. The operators Q k , P − k form a canonical conjugate pair and feature the following expectation values in the initial density matrix…”

Section: Effective Action: Fermionic Influence Functionalmentioning

confidence: 99%

Section: Motivations and Objectivesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fermionic influence on inflationary fluctuations

Boyanovsky

2016

Phys. Rev. D

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Open EFTs, IR effects & late-time resummations: systematic corrections in stochastic inflation

Burgess¹,

Holman²,

Tasinato³

2016

J. High Energ. Phys.

124

122

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Though simple inflationary models describe the CMB well, their corrections are often plagued by infrared effects that obstruct a reliable calculation of late-time behaviour. We adapt to cosmology tools designed to address similar issues in other physical systems with the goal of making reliable late-time inflationary predictions. The main such tool is Open EFTs which reduce in the inflationary case to Stochastic Inflation plus calculable corrections. We apply this to a simple inflationary model that is complicated enough to have dangerous IR behaviour yet simple enough to allow the inference of late-time behaviour. We find corrections to standard Stochastic Inflationary predictions for the noise and drift, and we find these corrections ensure the IR finiteness of both these quantities. The latetime probability distribution, P(φ), for super-Hubble field fluctuations are obtained as functions of the noise and drift and so these too are IR finite. We compare our results to other methods (such as large-N models) and find they agree when these models are reliable. In all cases we can explore in detail we find IR secular effects describe the slow accumulation of small perturbations to give a big effect: a significant distortion of the late-time probability distribution for the field. But the energy density associated with this is only of order H 4 at late times and so does not generate a dramatic gravitational back-reaction.

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Hot cosmic qubits: late-time de Sitter evolution and critical slowing down

Kaplanek

Burgess

2020

J. High Energ. Phys.

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Temporal evolution of a comoving qubit coupled to a scalar field in de Sitter space is studied with an emphasis on reliable extraction of late-time behaviour. The phenomenon of critical slowing down is observed if the effective mass is chosen to be sufficiently close to zero, which narrows the window of parameter space in which the Markovian approximation is valid. The dynamics of the system in this case are solved in a more general setting by accounting for non-Markovian effects in the evolution of the qubit state. Self-interactions for the scalar field are also incorporated, and reveal a breakdown of late-time perturbative predictions due to the presence of secular growth.

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Effective field theory during inflation: Reduced density matrix and its quantum master equation

Cited by 97 publications

References 101 publications

Fermionic influence on inflationary fluctuations

Fermionic influence on inflationary fluctuations

Open EFTs, IR effects & late-time resummations: systematic corrections in stochastic inflation

Hot cosmic qubits: late-time de Sitter evolution and critical slowing down

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