Non-Gaussianity of General Multiple-Field Inflationary Models

Sun, Chaoyi; Zhang, D. H.

doi:10.1142/s0218271806008887

Cited by 8 publications

(6 citation statements)

References 16 publications

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“…Are there interesting enhancements of non-Gaussian effects in these models? Estimates of the three-point function have been made by a number of authors [14][15][16][17][18], but as yet no complete formalism exists which allows the bispectrum to be followed from horizon-crossing up to the time of observation. Moreover, Gong & Tanaka recently pointed out that the most widely-used formulation of nonlinear perturbation theory is not covariant [19].…”

Section: Introductionmentioning

confidence: 99%

The inflationary bispectrum with curved field-space

Elliston

Seery

Tavakol

2012

J. Cosmol. Astropart. Phys.

126

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Abstract. We compute the covariant three-point function near horizon-crossing for a system of slowly-rolling scalar fields during an inflationary epoch, allowing for an arbitrary field-space metric. We show explicitly how to compute its subsequent evolution using a covariantized version of the separate universe or 'δN ' expansion, which must be augmented by terms measuring curvature of the field-space manifold, and give the nonlinear gauge transformation to the comoving curvature perturbation. Nonlinearities induced by the field-space curvature terms are a new and potentially significant source of non-Gaussianity. We show how inflationary models with non-minimal coupling to the spacetime Ricci scalar can be accommodated within this framework. This yields a simple toolkit allowing the bispectrum to be computed in models with non-negligible field-space curvature.

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Section: Introductionmentioning

confidence: 99%

The inflationary bispectrum with curved field-space

Elliston

Seery

Tavakol

2012

J. Cosmol. Astropart. Phys.

126

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“…They provided covariant formulae for the bispectrum of the field fluctuations at horizon crossing and extended the δN formalism [4,5,6,9] to provide a generalisation of the well-known δN result for the trivial field space metric [10] to a curved one. There have been previous studies of non-Gaussianity from a curved field space metric, but none so general or providing explicitly covariant results, see for example [11].…”

Section: Introductionmentioning

confidence: 99%

General formula for the running of local fNL

Byrnes¹,

Gong²

2013

Physics Letters B

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We compute the scale dependence of f NL for models of multi-field inflation, allowing for an arbitrary field space metric. We show that, in addition to multi-field effects and self interactions, the curved field space metric provides another source of scale dependence, which arises from the field-space Riemann curvature tensor and its derivatives. The scale dependence may be detectable within the near future if the amplitude of f NL is not too far from the current observational bounds.

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“…Indeed, in models descending from the low-energy limit of superstring theory or string compactification, there are many light moduli fields describing the higher-dimensional degrees of freedom, which could play a role during inflation. Therefore, it is interesting and of physical significance to generalize the above analysis of non-Gaussianities in single-field models to the multiple-field inflation models [29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47]. Most of the previous works focus on the models with standard canonical kinetic terms for the scalar fields involved.…”

Section: Introductionmentioning

confidence: 99%

“…Models with non-canonical kinetic terms have also been investigated, in particular the effective multiple-field DBI-inflation [45,46,47]. Models with non-trivial field space metric G IJ have also been considered [40].…”

Section: Introductionmentioning

confidence: 99%

Primordial non-Gaussianities of general multiple-field inflation

Gao

2008

J. Cosmol. Astropart. Phys.

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We perform a general study of the primordial scalar non-Gaussianities in multi-field inflationary models in Einstein gravity. We consider models governed by a Lagrangian which is a general function of the scalar fields and their first-order spacetime derivatives. We use δN formalism to relate scalar fields and the curvature perturbations. We calculate the explicit cubic-order perturbative action and the three-point function of curvature perturbation evaluated at the horizon-crossing. Under reasonable assumptions, in the small slow-varying parameters limit and with a sound speed c s close to one, we find that the non-Gaussianity is completely determined by these slow-varying parameters and some other parameters which are determined by the structure of the inflationary model. Our work generalizes previous results, and implies the possibility of the existence of large non-Gaussianity in model constructing, and it would be also useful to study the non-Gaussianity in multi-field inflationary models which will be constructed in the future.

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Non-Gaussianity of General Multiple-Field Inflationary Models

Abstract: Using the "δN -formalism," we obtain the expression of the non-Gaussianity of multiplefield inflationary models with the non-trivial field-space metric. Further, we have rewritten the result by using the slow-rolling approximation.

Cited by 8 publications

References 16 publications

The inflationary bispectrum with curved field-space

The inflationary bispectrum with curved field-space

General formula for the running of local fNL

Primordial non-Gaussianities of general multiple-field inflation

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