Particle production during inflation: Observational constraints and signatures

Abstract

In a variety of inflation models the motion of the inflaton may trigger the production of some noninflaton 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 non-Gaussianities. Here we focus on a prototype scenario with inflaton, $\ensuremath{\phi}$, and isoinflaton, $\ensuremath{\chi}$, fields interacting during inflation via the coupling ${g}^{2}(\ensuremath{\phi}\ensuremath{-}{\ensuremath{\phi}}_{0}{)}^{2}{\ensuremath{\chi}}^{2}$. 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 microscopically well-motivated inflation model. Our prototype scenario predicts a bumplike 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 using a variety of cosmological data sets. We find that bumps with amplitudes as large as $\mathcal{O}(10%)$ of the usual scale-invariant fluctuations from inflation, corresponding to ${g}^{2}\ensuremath{\sim}0.01$, are allowed on scales relevant for cosmic microwave background experiments. Our results imply an upper limit on the coupling ${g}^{2}$ (for a given ${\ensuremath{\phi}}_{0}$) which is crucial for assessing the detectability of the non-Gaussianity 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.