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

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">S&#xe9;bastien 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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