A single field inflation model with large local non-Gaussianity

Chen, Xingang; Firouzjahi, Hassan; Namjoo, Mohammad Hossein; Sasaki, Misao

doi:10.1209/0295-5075/102/59001

Cited by 136 publications

(200 citation statements)

References 33 publications

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“…In a precise sense is at the top of the Hubble hierarchy in that the condition < 1 determines the very existence of a background that is undergoing accelerated expansion. Although η being small is colloquially considered one of the requisites of 'slow roll' inflation, this is not strictly true as η 1 merely guarantees a sufficiently long period of slow roll if it and are both roughly constant (see [155] for an illustration of a background where is small and fast decreasing with η of order unity). In other words, indicates whether inflation is happening at a given instant whereas η indicates whether inflation will continue to happen in the future if both slow roll parameters remain constant.…”

Section: Effective Potential Modulations and Phase Transitionsmentioning

confidence: 99%

Features and new physical scales in primordial observables: Theory and observation

Chluba

Hamann

Patil

2015

Int. J. Mod. Phys. D

212

233

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June 22, 20152 All cosmological observations to date are consistent with adiabatic, Gaussian and nearly scale invariant initial conditions. These findings provide strong evidence for a particular symmetry breaking pattern in the very early universe (with a close to vanishing order parameter, ), widely accepted as conforming to the predictions of the simplest realizations of the inflationary paradigm. However, given that our observations are only privy to perturbations, in inferring something about the background that gave rise to them, it should be clear that many different underlying constructions project onto the same set of cosmological observables. Features in the primordial correlation functions, if present, would offer a unique and discriminating window onto the parent theory in which the mechanism that generated the initial conditions is embedded. In certain contexts, simple linear response theory allows us to infer new characteristic scales from the presence of features that can break the aforementioned degeneracies among different background models, and in some cases can even offer a limited spectroscopy of the heavier degrees of freedom that couple to the inflaton. In this review, we offer a pedagogical survey of the diverse, theoretically well grounded mechanisms which can imprint features into primordial correlation functions in addition to reviewing the techniques one can employ to probe observations. These observations include cosmic microwave background anisotropies and spectral distortions as well as the matter two and three point functions as inferred from large-scale structure and potentially, 21 cm surveys.

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Section: Effective Potential Modulations and Phase Transitionsmentioning

confidence: 99%

Features and new physical scales in primordial observables: Theory and observation

Chluba

Hamann

Patil

2015

Int. J. Mod. Phys. D

212

233

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“…Afterwards, the consistency relation was derived in a rather general setup of single field models of inflation [15], while several examples that do not satisfy the consistency relation were also reported [34][35][36] (see also refs. [37,38]).…”

Section: Condition For Consistency Relationmentioning

confidence: 99%

Large gauge transformation, soft theorem, and Infrared divergence in inflationary spacetime

Tanaka

Urakawa

2017

J. High Energ. Phys.

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It is widely known that the primordial curvature perturbation ζ has several universal properties in the infrared (IR) such as the soft theorem, which is also known as the consistency relation, and the conservation in time. They are valid in rather general single clock models of inflation. It has been argued that these universal properties are deeply related to the large gauge transformations in inflationary spacetime. However, the invariance under the large gauge transformations is not sufficient to show these IR properties. In this paper, we show that the locality condition is crucial to show the consistency relation and the conservation of ζ. This argument also can apply to an interacting system with the inflaton and heavy fields which have arbitrary integer spins, including higher spin fields, which may be motivated from string theory. We will also show that the locality condition guarantees the cancellation of the IR divergences in a certain class of variables whose correlation functions resemble cosmologically observable quantities.

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“…In [16,17], a standard kinetic term is considered and the local non-Gaussianity is still f NL ∼ 1. On the other hand, one can consider the single field inflation with small sound speed [18]. In this specific model the local non-Gaussianity is boosted into f NL ∼ 1/c 2 s .…”

Section: Pacs Numbersmentioning

confidence: 99%

“…In the model of [18], λ/Σ = 1/(6c 2 s ), and µ/Σ = 1/(12c 4 s ). In this case the non-Gaussian estimators are…”

Section: Pacs Numbersmentioning

confidence: 99%

Large local non-Gaussianity from general ultra slow-roll inflation

Huang

Wang

2013

J. Cosmol. Astropart. Phys.

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We investigate the non-Gaussian signatures of ultra slow-roll inflation. The bispectrum and the trispectrum are calculated with general initial conditions. The trispectrum is of local shape, as in the case of the bispectrum. We show that the prediction of local non-Gaussianity is robust again generalizing the Bunch-Davies vacuum. The Suyama-Yamaguchi relation is saturated in this scenario. PACS numbers:Inflation [1-3] generates remarkably Gaussian fluctuations [4]. While the departure from the Gaussianity plays a key role in classifying inflation models [5,6]. The non-Gaussianities generated in the primordial epoch can be characterized by their shapes. For example, the local shape non-Gaussianity [7,8] indicates large super-Hubble interactions; equilateral [9] or orthogonal [10] shapes indicate modifications of the kinetic Lagrangian of the inflaton; intermediate shapes [11,12] are signs of existence for interacting sectors with energy scale of order Hubble; and a folded shape [9] arises from modified initial conditions.To relate inflationary models to observations, on the one hand, it is important to find out which model better fits data. On the other hand, it is equally (if not more) important to be able to rule out classes of models, with general assumptions. Consistency relations for non-Gaussianities are here in position for the ability to rule out models.The best studied consistency relation for non-Gaussianity is the Maldacena's squeezed limit [8,13,14]: In a 3-point function ζ k1 ζ k2 ζ k3 , when one of the mode has wavelength much greater than the other two (say, k 1 k 2 k 3 ), at the horizon crossing time of k 2 and k 3 , the mode k 1 is already super-Hubble and thus behaves as a shift of background. For single field inflation, this shift of background can be characterized fully by a modified Hubble crossing time for mode k 2 and k 3 . As a result, the 3-point function ζ k1 ζ k2 ζ k3 can be calculated from the scale dependence of the power spectrum asThis consistency relation can be understood as a no-go theorem, obstructing single field inflation to produce large local non-Gaussianities. However, no-go theorems are no better than their assumptions. When assuming the long wave length mode behaves as a shift of background, one need to be careful about the differences between a long wave length mode and a shift of background. The differences include:• The long wave length mode exits the horizon at an earlier time during inflation. However, a shift of background never exits the horizon. Thus initial correlations between k 1 and k 2 , k 3 , if not suppressed in the k 1 /k 2 → 0 limit, may provide a violation of the no-go theorem. There is indeed known counter example of this type: by allowing non-Bunch-Davies initial conditions for inflation [9].• The dynamics of the background scale factor is governed by the Friedmann equation, which is a first order differential equation, with only one mode (i.e. only one integration constant). However, the long wave length perturbation satisfies a second order different...

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A single field inflation model with large local non-Gaussianity

Cited by 136 publications

References 33 publications

Features and new physical scales in primordial observables: Theory and observation

Features and new physical scales in primordial observables: Theory and observation

Large gauge transformation, soft theorem, and Infrared divergence in inflationary spacetime

Large local non-Gaussianity from general ultra slow-roll inflation

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