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Equilateral Non-Gaussianity and New Physics on the Horizon

Daniel Baumann, Daniel Green

Abstract

We examine the effective theory of single-field inflation in the limit where the scalar perturbations propagate with a small speed of sound. In this case the non-linearly realized time-translation symmetry of the Lagrangian implies large interactions, giving rise to primordial non-Gaussianities. When the non-Gaussianities are measurable, these interactions will become strongly coupled unless new physics appears close to the Hubble scale. Due to its proximity to the Hubble scale, the new physics is not necessarily decoupled from inflationary observables and can potentially affect the predictions of the model. To understand the types of corrections that may arise, we construct weakly-coupled completions of the theory and study their observational signatures.

Equilateral Non-Gaussianity and New Physics on the Horizon

Abstract

We examine the effective theory of single-field inflation in the limit where the scalar perturbations propagate with a small speed of sound. In this case the non-linearly realized time-translation symmetry of the Lagrangian implies large interactions, giving rise to primordial non-Gaussianities. When the non-Gaussianities are measurable, these interactions will become strongly coupled unless new physics appears close to the Hubble scale. Due to its proximity to the Hubble scale, the new physics is not necessarily decoupled from inflationary observables and can potentially affect the predictions of the model. To understand the types of corrections that may arise, we construct weakly-coupled completions of the theory and study their observational signatures.

Paper Structure

This paper contains 36 sections, 164 equations, 4 figures.

Table of Contents

  1. Introduction
  2. The Effective Theory of Inflation
  3. Goldstone Description of Inflation
  4. A Gauge Theory Analogy
  5. Decoupling Limit
  6. Energy Scales
  7. Symmetry Breaking
  8. Strong Coupling
  9. A Hint of New Physics?
  10. New Physics near Hubble
  11. Preliminary Remarks
  12. Weakly-Coupled UV-Completions
  13. The $\pi$-$\sigma$ Model
  14. Extrinsic Curvature Terms
  15. Observational Consequences
  16. ...and 21 more sections

Figures (4)

  • Figure 1: Relevant energy scales in single-field inflation with small speed of sound.
  • Figure 2: Relevant energy scales in the $\pi$-$\sigma$ model.
  • Figure 3: Relevant energy scales in the model with extrinsic curvature terms.
  • Figure 4: Comparison between the shape produced by the dominant higher-derivative correction in both UV-completions, the equilateral shape and the orthogonal shape. All shapes are normalized relative to the amplitude in the equilateral configuration.