Flattened non-Gaussianities from the effective field theory of inflation with imaginary speed of sound

García-Sáenz, Sebastián; Renaux‐Petel, Sébastien

doi:10.1088/1475-7516/2018/11/005

Cited by 49 publications

(97 citation statements)

References 57 publications

(112 reference statements)

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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: 97%

Revisiting non-Gaussianity in multifield inflation with curved field space

García-Sáenz

Pinol

Renaux‐Petel

2020

J. High Energ. Phys.

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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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Section: Generalities and Regime Of Validitymentioning

confidence: 97%

Revisiting non-Gaussianity in multifield inflation with curved field space

García-Sáenz

Pinol

Renaux‐Petel

2020

J. High Energ. Phys.

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“…In the single-field EFT with an imaginary speed of sound, the mode function of the curvature perturbation can be written as [10,12]…”

Section: Hyper-large Non-gaussianities?mentioning

confidence: 99%

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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“…Folded non-Gaussianity is known to arise in the scalar sector of specific models of inflation, see e.g. [34][35][36][37]. It would be interesting to investigate models where the same shape of nG arise in the tensor sector, for example in models with extra spin-2 degrees of freedom in an EFT approach to inflation (see e.g.…”

Section: Characterization Of a Stationary Non-gaussian Sgwbmentioning

confidence: 99%

Probing a stationary non-Gaussian background of stochastic gravitational waves with pulsar timing arrays

Powell

Tasinato

2020

J. Cosmol. Astropart. Phys.

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We introduce the concept of stationary graviton non-Gaussianity (nG), an observable that can be probed in terms of 3-point correlation functions of a stochastic gravitational wave (GW) background. When evaluated in momentum space, stationary nG corresponds to folded bispectra of graviton nG. We determine 3-point overlap functions for testing stationary nG with pulsar timing array GW experiments, and we obtain the corresponding optimal signal-tonoise ratio. For the first time, we consider 3-point overlap functions including scalar graviton polarizations (which can be motivated in theories of modified gravity); moreover, we also calculate 3-point overlap functions for correlating pulsar timing array with ground based GW detectors. The value of the optimal signal-to-noise ratio depends on the number and position of monitored pulsars. We build geometrical quantities characterizing how such ratio depends on the pulsar system under consideration, and we evaluate these geometrical parameters using data from the IPTA collaboration. We quantitatively show how monitoring a large number of pulsars can increase the signal-to-noise ratio associated with measurements of stationary graviton nG. arXiv:1910.04758v1 [gr-qc]

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Flattened non-Gaussianities from the effective field theory of inflation with imaginary speed of sound

Cited by 49 publications

References 57 publications

Revisiting non-Gaussianity in multifield inflation with curved field space

Revisiting non-Gaussianity in multifield inflation with curved field space

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

Probing a stationary non-Gaussian background of stochastic gravitational waves with pulsar timing arrays

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