Primordial fluctuations and non-Gaussianities in sidetracked inflation

García-Sáenz, Sebastián; Renaux‐Petel, Sébastien; Ronayne, J. W.

doi:10.1088/1475-7516/2018/07/057

Cited by 94 publications

(187 citation statements)

References 99 publications

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“…We close this paper with a general, analytic WKB computation of the growth of the perturbations in the two-field theory with strong turning. Our result agrees with the numerical analysis of [2], and gives further evidence for the correctness of the single-field effective field theory with imaginary speed of sound developed and used in [9,10,12].…”

Section: Introductionsupporting

confidence: 87%

Mild non-Gaussianities under perturbative control from rapid-turn inflation models

Bjorkmo

Ferreira

Marsh

2019

J. Cosmol. Astropart. Phys.

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Inflation can be supported in very steep potentials if it is generated by rapidly turning fields, which can be natural in negatively curved field spaces. The curvature perturbation, ζ, of these models undergoes an exponential, transient amplification around the time of horizon crossing, but can still be compatible with observations at the level of the power spectrum. However, a recent analysis (based on a proposed single-field effective theory with an imaginary speed of sound) found that the trispectrum and other higher-order, non-Gaussian correlators also undergo similar exponential enhancements. This arguably leads to 'hyper-large' non-Gaussianities in stark conflict with observations, and even to the loss of perturbative control of the calculations. In this paper, we provide the first analytic solution of the growth of the perturbations in two-field rapid-turn models, and find it in good agreement with previous numerical and single-field EFT estimates. We also show that the nested structure of commutators of the in-in formalism has subtle and crucial consequences: accounting for these commutators, we show analytically that the naively leading-order piece (which indeed is exponentially large) cancels exactly in all relevant correlators. The remaining non-Gaussianities of these models are modest, and there is no problem with perturbative control from the exponential enhancement of ζ. Thus, rapidturn inflation with negatively curved field spaces remains a viable and interesting class of candidate theories of the early universe.

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Section: Introductionsupporting

confidence: 87%

Mild non-Gaussianities under perturbative control from rapid-turn inflation models

Bjorkmo

Ferreira

Marsh

2019

J. Cosmol. Astropart. Phys.

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“…As fat inflation models with large turning rates, we show an example of two-field natural inflation model discussed in [34] (AAW1), the recent three field model in [58] (APR) and the sidetrack models in [24]. These all have large Ω/H, and only the sidetrack models have a non-zero negative curvature R. In table 6 we show the ratio between the masses and the Hubble parameter for AW1, APR and the sidetrack models (both the minimal an hyperbolic examples have similar mass hierarchies).…”

Section: Discussionmentioning

confidence: 97%

“…Let us also point out that when more than two fields are present, one can define a turning rate associated to every normal direction and they will contribute to the total turning rate 10 Recent multifield inflation investigations have pointed out that small turning rates are not necessary for a successful period of slow-roll inflation [23][24][25][26][27][28], as we showed explicitly above. Most of these studies focus on the case of non-zero negative curvature of the scalar manifold.…”

Section: Slow-roll Fat Inflation and Large Turnsmentioning

confidence: 88%

Fat inflatons, large turns and the η-problem

Chakraborty

Chiovoloni

Loaiza-Brito

et al. 2020

J. Cosmol. Astropart. Phys.

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It is commonly believed that a successful period of inflation driven by a single or several scalar fields requires a specific hierarchy of masses given by M inf H M heavy , where M inf can correspond to several or a single light field and M heavy corresponds to any heavy field that might be integrated out if it satisfies suitable conditions. This is at the heart of the so called η-problem in inflation, since large contributions to the masses of the inflatons might spoil the slow-roll conditions required for inflation. We show that, while this is an unavoidable conclusion in single field inflation, in multifield inflation, heavy fields as defined above, may be fully responsible for a successful period of what we call fat slow-roll inflation. Moreover we show that in this scenario, the turning rate of the inflationary trajectory, Ω/H, is larger than one. Thus, the η-problem is evaded with large turns in fat inflation. Depending on the perturbations' mass spectra, cosmological predictions will differ either slightly or largely with respect to those of the single field case. We illustrate this scenario in a concrete example in Type IIB string flux compactifications, where a probe D5-brane moving along the angular and radial directions in a warped throat drives fat D5-brane natural inflation. An instantaneous superplanckian decay constant can be defined, consistent with our low energy approximations, thanks to the strong warping of the geometry. We compute the cosmological observables, which differ from the single field case. We also discuss fat inflation in the context of recently proposed swampland de Sitter conjectures.

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“…In a related manner, the expression of χ (2.11) in the two-field theory simply boils down to ∂ 2 χ LO /a 2 = ζ /c 2 s in the single-field EFT. We note that models giving rise to c 2 s < 0 -an imaginary sound speed -have been recently studied, as well as the implications of such a non-standard framework [26,28,88].…”

Section: Generalities and Regime Of Validitymentioning

confidence: 96%

Revisiting non-Gaussianity in multifield inflation with curved field space

2020

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Recent studies of inflation with multiple scalar fields have highlighted the importance of non-canonical kinetic terms in novel types of inflationary solutions. This motivates a thorough analysis of non-Gaussianities in this context, which we revisit here by studying the primordial bispectrum in a general two-field model. Our main result is the complete cubic action for inflationary fluctuations written in comoving gauge, i.e. in terms of the curvature perturbation and the entropic mode. Although full expressions for the cubic action have already been derived in terms of fields fluctuations in the flat gauge, their applicability is mostly restricted to numerical evaluations. Our form of the action is instead amenable to several analytical approximations, as our calculation in terms of the directly observable quantity makes manifest the scaling of every operator in terms of the slow-roll parameters, what is essentially a generalization of Maldacena's single-field result to non-canonical two-field models. As an important application we derive the single-field effective field theory that is valid when the entropic mode is heavy and may be integrated out, underlining the observable effects that derive from a curved field space.

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Primordial fluctuations and non-Gaussianities in sidetracked inflation

Cited by 94 publications

References 99 publications

Mild non-Gaussianities under perturbative control from rapid-turn inflation models

Mild non-Gaussianities under perturbative control from rapid-turn inflation models

Fat inflatons, large turns and the η-problem

Revisiting non-Gaussianity in multifield inflation with curved field space

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