The squeezed limit of the bispectrum in multi-field inflation

Kenton, Zachary; Mulryne, David J.

doi:10.1088/1475-7516/2015/10/018

Cited by 24 publications

(43 citation statements)

References 135 publications

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“…where the first line again matches the standard result [45,46]. In contrast, note that this standard result cannot be obtained within the usual classical δN formalism because of the intrinsic non-Gaussianity of the field at Hubble exit [45,47].…”

Section: Introductionsupporting

confidence: 79%

Critical Number of Fields in Stochastic Inflation

et al. 2017

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Stochastic effects in generic scenarios of inflation with multiple fields are investigated. First passage time techniques are employed to calculate the statistical moments of the number of inflationary e-folds, which give rise to all correlation functions of primordial curvature perturbations through the stochastic δN formalism. The number of fields is a critical parameter. The probability of exploring arbitrarily large-field regions of the potential becomes non-vanishing when more than two fields are driving inflation. The mean number of e-folds can be infinite, depending on the number of fields; for plateau potentials, this occurs even with one field. In such cases, correlation functions of curvature perturbations are infinite. They can, however, be regularised if a reflecting (or absorbing) wall is added at large energy or field value. The results are found to be independent of the exact location of the wall and this procedure is, therefore, well-defined for a wide range of cutoffs, above or below the Planck scale. Finally, we show that, contrary to single-field setups, multi-field models can yield large stochastic corrections even at sub-Planckian energy, opening interesting prospects for probing quantum effects on cosmological fluctuations. IntroductionIn the inflationary paradigm [1-6], cosmological inhomogeneities result from the parametric amplification of the vacuum quantum fluctuations of the gravitational and matter fields during an early accelerated expansion [7][8][9][10][11][12]. The transition from quantum fluctuations to classical but stochastic density perturbations [13][14][15][16][17][18] plays an important role in this scenario. In particular, it implies that the open quantum system comprising the superHubble degrees of freedom can be described with a classical stochastic theory, the stochastic inflation formalism [10,[19][20][21][22][23][24][25][26][27]. This consists of an effective description of the long-wavelength parts of the quantum fields, which are "coarse grained" at a fixed physical scale, larger than the Hubble radius during the whole inflationary era. In this framework, the short-wavelength quantum fluctuations act as a classical noise on the dynamics of the super-Hubble scales, and at leading order in slow roll, the coarse-grained fields φ i follow Langevin equations

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Section: Introductionsupporting

confidence: 79%

Critical Number of Fields in Stochastic Inflation

et al. 2017

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“…Note that this expression is essentially a (covariantised) version of the standard δ N expression for f NL [38], which there corresponds to a quasi-local configuration for the bispectrum (close, but not identical, to the local one -cf. the discussion in [39]). Taking (49) and noting that one can write N ,A = UU ,A /(U ,B U ,B ) [23], after some algebra we then find that f local NL can in fact succinctly be expressed as…”

Section: Observables and Single Field Dynamicsmentioning

confidence: 92%

Inflation in a scale-invariant universe

et al. 2018

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A scale-invariant universe can have a period of accelerated expansion at early times: inflation. We use a frame-invariant approach to calculate inflationary observables in a scale-invariant theory of gravity involving two scalar fields: the spectral indices, the tensor-to-scalar ratio, the level of isocurvature modes, and non-Gaussianity. We show that scale symmetry leads to an exact cancellation of isocurvature modes and that, in the scale symmetry-broken phase, this theory is well described by a single scalar-field theory. We find the predictions of this theory strongly compatible with current observations.

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“…However, since we are primarily interested in local non-Gaussianity which is confirmed on super-horizon scales, we skip over this term. Whilst f (4) N L is momentum independent parameter and accounts for the super-horizon contribution (one can refer to [45,46] for more discussions).…”

Section: Local Non-gaussianity Using δN Formalismmentioning

confidence: 99%

The size of local bispectrum and trispectrum in a non-minimal inflation

Asadi

Nozari

2018

Nuclear Physics B

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Focusing on the local type primordial non-Gaussianities, we study the bispectrum and trispectrum during a non-minimal slow-roll inflation. We use the so-called δN formalism to investigate the super-horizon evolution of the primordial perturbations in this setup. Firstly we obtain the main equations of the model and introduce the framework of the δN formalism for this case. Then we give analytical expressions for the nonlinear parameters describing the non-Gaussianity in the slowroll approximation. We analyze the bispectrum by its non-linear parameter, fNL. Furthermore, we calculate τNL and gNL which are non-linear parameters characterizing the amplitude of trispectrum. Finally, by adopting a quadratic form for both the potential and non-minimal coupling (NMC) function, we test our setup in the light of Planck2015 data and constrain the model parameters space. Although the non-Gaussianity parameters are so small in this setup, this model is consistent with recent observation. We extend our analysis to see the situation in the Einstein frame and compare the results in these two frames.PACS numbers: 98.80.Cq , 98.80.Es

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The squeezed limit of the bispectrum in multi-field inflation

Cited by 24 publications

References 135 publications

Critical Number of Fields in Stochastic Inflation

Critical Number of Fields in Stochastic Inflation

Inflation in a scale-invariant universe

The size of local bispectrum and trispectrum in a non-minimal inflation

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