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Primordial perturbations and non-Gaussianities from modulated trapping

David Langlois, Lorenzo Sorbo

TL;DR

Langlois and Sorbo introduce modulated trapping as a novel route to generate primordial curvature perturbations during inflation via resonant particle production whose strength is modulated by a light field, the modulaton $\sigma$. Using the $\delta N$ formalism, they show that the total curvature perturbation is a sum of the standard inflaton contribution and a trap-induced term, with the latter potentially dominating under certain couplings. They derive explicit expressions for the power spectrum and the bispectrum/trispectrum, finding that non-Gaussianities scale as $f_{NL} \propto \Xi^2$ and $\tau_{NL}, g_{NL} \propto \Xi^3$, and identify parameter regimes where detectable non-Gaussianities arise. The work provides a concrete framework for converting isocurvature perturbations into adiabatic fluctuations through backreaction effects during inflation, with distinctive observational signatures depending on how the modulaton couples to the production process.

Abstract

We propose a new mechanism to generate primordial curvature perturbations, based on the resonant production of particles during inflation. It is known that this phenomenon can trap the inflaton for a fraction of e-fold. This effect is governed by the mass of the produced particles and by their coupling to the inflaton, parameters which can depend on the expectation value of other fields. If one of such additional fields - a 'modulaton' - is light, then its fluctuations, acquired during the earlier stages of inflation, will induce a spatial modulation of the trapping, and thus of the end of inflation, corresponding to a curvature perturbation. We calculate the power spectrum, bispectrum and trispectrum of the curvature perturbations generated by this mechanism, taking into account the perturbations due to the inflaton fluctuations as well. We find that modulated trapping could provide the main contribution to the observed power spectrum and lead to detectable primordial non-gaussianities.

Primordial perturbations and non-Gaussianities from modulated trapping

TL;DR

Langlois and Sorbo introduce modulated trapping as a novel route to generate primordial curvature perturbations during inflation via resonant particle production whose strength is modulated by a light field, the modulaton . Using the formalism, they show that the total curvature perturbation is a sum of the standard inflaton contribution and a trap-induced term, with the latter potentially dominating under certain couplings. They derive explicit expressions for the power spectrum and the bispectrum/trispectrum, finding that non-Gaussianities scale as and , and identify parameter regimes where detectable non-Gaussianities arise. The work provides a concrete framework for converting isocurvature perturbations into adiabatic fluctuations through backreaction effects during inflation, with distinctive observational signatures depending on how the modulaton couples to the production process.

Abstract

We propose a new mechanism to generate primordial curvature perturbations, based on the resonant production of particles during inflation. It is known that this phenomenon can trap the inflaton for a fraction of e-fold. This effect is governed by the mass of the produced particles and by their coupling to the inflaton, parameters which can depend on the expectation value of other fields. If one of such additional fields - a 'modulaton' - is light, then its fluctuations, acquired during the earlier stages of inflation, will induce a spatial modulation of the trapping, and thus of the end of inflation, corresponding to a curvature perturbation. We calculate the power spectrum, bispectrum and trispectrum of the curvature perturbations generated by this mechanism, taking into account the perturbations due to the inflaton fluctuations as well. We find that modulated trapping could provide the main contribution to the observed power spectrum and lead to detectable primordial non-gaussianities.

Paper Structure

This paper contains 10 sections, 62 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Model and homogeneous solution
  3. Fluctuations
  4. The power spectrum
  5. Modulaton-independent coupling
  6. Modulaton-dependent coupling
  7. Non-Gaussianities
  8. Modulaton-independent coupling
  9. Modulaton-dependent coupling
  10. Conclusions

Figures (2)

  • Figure 1: Evolution of $|\dot\phi|$ as a function of the number of e-folds $N$ for a model of chaotic inflation with trapping (lower curve) and without trapping (upper curve).
  • Figure 2: Evolution of $\phi$ as a function of the number of e-folds $N$ with trapping (upper curve) and without trapping (lower curve), using the same model and initial conditions as in Fig. 1.