Particle production during inflation: Observational constraints and signatures

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, phi, and isoinflaton, 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 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 O(10%) of the usual scale-invariant fluctuations from inflation, corresponding to g(2)similar to 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 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.