DBI in the sky: Non-Gaussianity from inflation with a speed limit

Alishahiha, Mohsen; Silverstein, Eva; Tong, David

doi:10.1103/physrevd.70.123505

Cited by 904 publications

(1,214 citation statements)

References 46 publications

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“…Furthermore, by extending the analysis to the slow-roll inflation, we find that parity violation in the bispectrum does not vanish and its magnitude is proportional to the slow roll parameter. Although the parity violation we found is small in the case of slow-roll inflationary scenario, it can become significant in the non-standard inflations such as Dirac-Born-Infeld inflation [20,21]. Much larger parity violation is also expected to occur in the recently developed effective field theory approaches [22,23,24] to which our formulation can be also applicable.…”

Section: Introductionmentioning

confidence: 76%

Parity violation in graviton non-gaussianity

Soda

Kodama

Nozawa

2011

J. High Energ. Phys.

112

109

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Abstract:We study parity violation in graviton non-gaussianity generated during inflation. We develop a useful formalism to calculate graviton non-gaussianity. Using this formalism, we explicitly calculate the parity violating part of the bispectrum for primordial gravitational waves in the exact de Sitter spacetime and prove that no parity violation appears in the non-gaussianity. We also extend the analysis to slow-roll inflation and find that the parity violation of the bispectrum is proportional to the slow-roll parameter. We argue that parity violating non-gaussianity can be tested by the CMB. Our results are also useful for calculating three-point function of the stress tensor in the non-conformal field theory through the gravity/field theory correspondence.

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Section: Introductionmentioning

confidence: 76%

Parity violation in graviton non-gaussianity

Soda

Kodama

Nozawa

2011

J. High Energ. Phys.

112

109

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“…DBI inflationary models based on string theory Alishahiha et al 2004) provide physically well-motivated examples of the P(X, φ)-model. They are characterized by an almost equilateral NG with f equil NL = −(35/108)c −2 s for c s 1, which typically is f equil NL < −5.…”

Section: General Single-field Models Of Inflationmentioning

confidence: 99%

Planck2015 results

Ade

Aghanim

Arnaud

et al. 2016

A&A

472

256

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The Planck full mission cosmic microwave background (CMB) temperature and E-mode polarization maps are analysed to obtain constraints on primordial non-Gaussianity (NG). Using three classes of optimal bispectrum estimators -separable template-fitting (KSW), binned, and modalwe obtain consistent values for the primordial local, equilateral, and orthogonal bispectrum amplitudes, quoting as our final result from temperature alone f local NL = 2.5 ± 5.7, f equil NL = −16 ± 70, and f ortho NL = −34 ± 33 (68% CL, statistical). Combining temperature and polarization data we obtain f local NL = 0.8 ± 5.0, f equil NL = −4 ± 43, and f ortho NL = −26 ± 21 (68% CL, statistical). The results are based on comprehensive cross-validation of these estimators on Gaussian and non-Gaussian simulations, are stable across component separation techniques, pass an extensive suite of tests, and are consistent with estimators based on measuring the Minkowski functionals of the CMB. The effect of time-domain de-glitching systematics on the bispectrum is negligible. In spite of these test outcomes we conservatively label the results including polarization data as preliminary, owing to a known mismatch of the noise model in simulations and the data. Beyond estimates of individual shape amplitudes, we present model-independent, three-dimensional reconstructions of the Planck CMB bispectrum and derive constraints on early universe scenarios that generate primordial NG, including general single-field models of inflation, axion inflation, initial state modifications, models producing parityviolating tensor bispectra, and directionally dependent vector models. We present a wide survey of scale-dependent feature and resonance models, accounting for the "look elsewhere" effect in estimating the statistical significance of features. We also look for isocurvature NG, and find no signal, but we obtain constraints that improve significantly with the inclusion of polarization. The primordial trispectrum amplitude in the local model is constrained to be g local NL = (−9.0 ± 7.7) × 10 4 (68% CL statistical), and we perform an analysis of trispectrum shapes beyond the local case. The global picture that emerges is one of consistency with the premises of the ΛCDM cosmology, namely that the structure we observe today was sourced by adiabatic, passive, Gaussian, and primordial seed perturbations.

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“…[12,13] (see [14,15] for earlier studies under slow-roll approximation). A distinguishing feature of the model in this type is that a large positive nonlocal non-Gaussianity can be obtained due to an enhancement of a small sound speed for the perturbation [16,17], which is in contrast to the prediction of a canonical single-field inflation model [18]. Established on the scenario of multiple brane inflation [12,13] and motivated by the model of spinflation [19], an explicit construction of the curvaton brane model was recently realized in Ref.…”

Section: Introductionmentioning

confidence: 99%

Large nonlocal non-Gaussianity from a curvaton brane

Cai

Wang

2010

Phys. Rev. D

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We use a generalized N formalism to study the generation of the primordial curvature perturbation in the curvaton brane scenario inspired by stringy compactifications. We note that the non-Gaussian features, especially the trispectra, crucially depend on the decay mechanism in a general curvaton scenario. Specifically, we study the bispectra and trispectra of the curvaton brane model in detail to illustrate the importance of curvaton decay in generating nonlinear fluctuations. When the curvaton brane moves nonrelativistically during inflation, the shape of non-Gaussianity is local, but the corresponding size is different from that in the standard curvaton scenario. When the curvaton brane moves relativistically in inflationary stage, the shape of non-Gaussianity is of equilateral type.

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DBI in the sky: Non-Gaussianity from inflation with a speed limit

Cited by 904 publications

References 46 publications

Parity violation in graviton non-gaussianity

Parity violation in graviton non-gaussianity

Planck2015 results

Large nonlocal non-Gaussianity from a curvaton brane

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