Abstract
We study the preheating of gauge fields in a simple axion monodromy model and compute the induced entropy perturbations and their effect on the curvature fluctuations. We find that the correction to the spectrum of curvature perturbations has a blue spectrum with index ns = 5/2. Hence, these induced modes are harmless for the observed structure of the universe. Since the spectrum is blue, there is the danger of overproduction of primordial black holes. However, we show that the observational constraints are easily satisfied.
Highlights
Axion monodromy inflation [1] may be the most promising way to obtain large field inflation in the context of superstring theory 1
Large field inflation models have the advantage over most small field models in that the inflationary slow-roll trajectory is a local attractor in initial condition space [5]
In addition to the axion field, gauge fields to which the axion couples via a Pontryagin term in the effective action
Summary
Axion monodromy inflation [1] (see [2]) may be the most promising way to obtain large field inflation in the context of superstring theory 1. On cosmological scales the amplitude of the induced curvature fluctuations must be smaller than the observed perturbations 2. This is easy to satisfy if the spectrum of the induced fluctuations is blue, as in our case. It was realized that the spectrum of these fluctuations is blue, and there are potential constraints on the theory due to possible over-production of primordial black holes. This has been studied e.g. in [10, 11] (see [12]). The same Pontryagin term leads to an inverse cascade [14] for cosmological magnetic fields, and it can be used to provide a scaling quintessence model for dark energy [15]
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