Oscillations in the CMB from axion monodromy inflation

Abstract

We study the CMB observables in axion monodromy inflation. These\nwell-motivated scenarios for inflation in string theory have monomial\npotentials over super-Planckian field ranges, with superimposed sinusoidal\nmodulations from instanton effects. Such periodic modulations of the potential\ncan drive resonant enhancements of the correlation functions of cosmological\nperturbations, with characteristic modulations of the amplitude as a function\nof wavenumber. We give an analytical result for the scalar power spectrum in\nthis class of models, and we determine the limits that present data places on\nthe amplitude and frequency of modulations. Then, incorporating an improved\nunderstanding of the realization of axion monodromy inflation in string theory,\nwe perform a careful study of microphysical constraints in this scenario. We\nfind that detectable modulations of the scalar power spectrum are commonplace\nin well-controlled examples, while resonant contributions to the bispectrum are\nundetectable in some classes of examples and detectable in others. We conclude\nthat resonant contributions to the spectrum and bispectrum are a characteristic\nsignature of axion monodromy inflation that, in favorable cases, could be\ndetected in near-future experiments.\n