Particle Production During Inflation: Observational Constraints and Signatures

TL;DR

This paper investigates how particle production during inflation can create observable features in the primordial power spectrum, constraining models and exploring potential signatures like bumps and non-gaussianities.

Contribution

It introduces a simple model predicting bump-like features in the power spectrum and provides observational constraints on the coupling strength and resulting non-gaussianities.

Findings

Bump-like features with up to 10% amplitude are allowed in CMB scales.

Upper limits on the coupling g^2 are derived from observational constraints.

Implications for string theory and inflation models like brane/axion monodromy are discussed.

Abstract

In a variety of inflation models the motion of the inflaton may trigger the production of some non-inflaton particles during inflation, for example via parametric resonance or a phase transition. Particle production during inflation leads to observables in the cosmological fluctuations, such as features in the primordial power spectrum and also nongaussianities. Here we focus on a prototype scenario with inflaton, \phi, and iso-inflaton, \chi, fields interacting during inflation via the coupling g^2 (\phi-\phi_0)^2\chi^2. Since several previous investigations have hinted at the presence of localized "glitches" in the observed primordial power spectrum, which are inconsistent with the simplest power-law model, it is interesting to determine the extent to which such anomalies can be explained by this simple and well-motivated model. Our prototype scenario predicts a bump-like feature in the primordial power spectrum, rather than an oscillatory "ringing" pattern as has previously been assumed. We discuss the observational constraints on such features. We find that bumps with amplitude as large as 10% of the usual scale invariant fluctuations from inflation are allowed on scales relevant for Cosmic Microwave Background experiments. Our results imply an upper limit on the coupling g^2 which is crucial for assessing the detectability of the nongaussianity produced by inflationary particle production. We also discuss more complicated features that result from superposing multiple instances of particle production. Finally, we point to a number of microscopic realizations of this scenario in string theory and supersymmetry and discuss the implications of our constraints for the popular brane/axion monodromy inflation models.