Hyper non-Gaussianities in inflation with strongly non-geodesic motion. (arXiv:1902.03221v1 [hep-th])

<a href="http://arxiv.org/find/hep-th/1/au:+Fumagalli_J/0/1/0/all/0/1">Jacopo Fumagalli</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Garcia_Saenz_S/0/1/0/all/0/1">Sebastian Garcia-Saenz</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Pinol_L/0/1/0/all/0/1">Lucas Pinol</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Renaux_Petel_S/0/1/0/all/0/1">Sébastien Renaux-Petel</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Ronayne_J/0/1/0/all/0/1">John Ronayne</a>

Several recent proposals to embed inflation into high-energy physics rely on

inflationary dynamics characterized by a strongly non-geodesic motion in

negatively curved field space. This naturally leads to a transient instability

of perturbations on sub-Hubble scales, and to their exponential amplification.

Supported by first-principle numerical computations, we demonstrate that a

non-standard single-field effective field theory with imaginary speed of sound

enables one to gain analytical insight into primordial non-Gaussianities in

this type of models. We show that the bispectrum is enhanced in flattened

configurations and, more importantly, that the trispectrum and all higher-order

correlation functions are exponentially amplified. These “hyper

non-Gaussianities”, whose amplitude we can relate to the amplification of the

tree-level power spectrum, can easily lead to a loss of perturbative control.

For example our results exclude the recent proposal of hyperinflation in its

most interesting incarnation that satisfies the de Sitter swampland conjecture.

More generally we provide powerful model-independent constraints on

non-standard inflationary attractors motivated by the search for ultraviolet

completions of inflation.

Several recent proposals to embed inflation into high-energy physics rely on

inflationary dynamics characterized by a strongly non-geodesic motion in

negatively curved field space. This naturally leads to a transient instability

of perturbations on sub-Hubble scales, and to their exponential amplification.

Supported by first-principle numerical computations, we demonstrate that a

non-standard single-field effective field theory with imaginary speed of sound

enables one to gain analytical insight into primordial non-Gaussianities in

this type of models. We show that the bispectrum is enhanced in flattened

configurations and, more importantly, that the trispectrum and all higher-order

correlation functions are exponentially amplified. These “hyper

non-Gaussianities”, whose amplitude we can relate to the amplification of the

tree-level power spectrum, can easily lead to a loss of perturbative control.

For example our results exclude the recent proposal of hyperinflation in its

most interesting incarnation that satisfies the de Sitter swampland conjecture.

More generally we provide powerful model-independent constraints on

non-standard inflationary attractors motivated by the search for ultraviolet

completions of inflation.

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