Mild Non-Gaussianities under Perturbative Control from Rapid-Turn Inflation Models

Abstract

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, $\zeta$, 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 $\zeta$. Thus, rapid-turn inflation with negatively curved field spaces remains a viable and interesting class of candidate theories of the early universe.

arXiv comment19 pages, 2 figures

References in corpus (31)

• Particle Physics Models of Inflation and the Cosmological Density Perturbation
• On the Geometry of the String Landscape and the Swampland
• A General Analytic Formula for the Spectral Index of the Density Perturbations produced during Inflation
• Adiabatic and entropy perturbations from inflation
• Features of heavy physics in the CMB power spectrum
• Scalar perturbations during multiple-field slow-roll inflation
• Perturbations in generalized multi-field inflation
• Effective theories of single field inflation when heavy fields matter
• The string swampland constraints require multi-field inflation
• Mass hierarchies and non-decoupling in multi-scalar field dynamics
• On the importance of heavy fields during inflation
• Heavy fields, reduced speeds of sound and decoupling during inflation
• Strongly Coupled Perturbations in Two-Field Inflationary Models
• Geometrical Destabilization of Inflation
• Hyperinflation
• Spinflation
• Primordial fluctuations and non-Gaussianities in sidetracked inflation
• Primordial perturbations from inflation with a hyperbolic field-space
• On the validity of the perturbative description of axions during inflation
• Hyper non-Gaussianities in inflation with strongly non-geodesic motion
• The rapid-turn inflationary attractor
• Angular inflation in multi-field $\alpha$-attractors
• Hyperinflation generalised: from its attractor mechanism to its tension with the `swampland conjectures'
• Landscape tomography through primordial non-Gaussianity
• Flattened non-Gaussianities from the effective field theory of inflation with imaginary speed of sound
• Sound Speed of Primordial Fluctuations in Supergravity Inflation
• Geometrical destabilization, premature end of inflation and Bayesian model selection
• Reconstructing the Inflationary Landscape with Cosmological Data
• Geometrical Destabilisation of Ultra-Light Axions in String Inflation
• A geometrical instability for ultra-light fields during inflation?
• On backreaction effects in geometrical destabilisation of inflation

Cited by in corpus (27)

• The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics
• Generating PBHs and small-scale GWs in two-field models of inflation
• Inflation and Primordial Black Holes
• Oscillations in the stochastic gravitational wave background from sharp features and particle production during inflation
• Turning in the landscape: a new mechanism for generating Primordial Black Holes
• Bootstrapping Multi-Field Inflation: non-Gaussianities from light scalars revisited
• A manifestly covariant theory of multifield stochastic inflation in phase space: solving the discretisation ambiguity in stochastic inflation
• Large power spectrum and primordial black holes in the effective theory of inflation
• On the inflationary massive field with a curved field manifold
• On Primordial Black Holes from Rapid Turns in Two-field Models
• Multi-field Inflation in High-Slope Potentials
• The Multi-Field, Rapid-Turn Inflationary Solution
• Non-Gaussianities in models of inflation with large and negative entropic masses
• Sudden braking and turning with a two-field potential bump: primordial black hole formation
• $\mathcal{N}$-field cosmology in hyperbolic field space: stability and general solutions
• Dynamical consistency conditions for rapid turn inflation
• Opening the reheating box in multifield inflation
• Dark Matter from Entropy Perturbations in Curved Field Space
• Enhanced power spectra from multi-field inflation
• Non-Gaussianity in rapid-turn multi-field inflation
• On the Consistency of Rapid-Turn Inflation
• Loops in inflation with strongly non-geodesic motion
• Generalised conditions for rapid-turn inflation
• Inflation with vector fields revisited: heavy entropy perturbations and primordial black holes
• Primordial black holes with anisotropic hair
• Separate universe in multifield inflation: a phase-space approach
• Primordial gravitational waves from excited states