Oscillations in the CMB from axion monodromy inflation

Abstract

We study the CMB observables in axion monodromy inflation. These well-motivated scenarios for inflation in string theory have monomial potentials over super-Planckian field ranges, with superimposed sinusoidal modulations from instanton effects. Such periodic modulations of the potential can drive resonant enhancements of the correlation functions of cosmological perturbations, with characteristic modulations of the amplitude as a function of wavenumber. We give an analytical result for the scalar power spectrum in this class of models, and we determine the limits that present data places on the amplitude and frequency of modulations. Then, incorporating an improved understanding of the realization of axion monodromy inflation in string theory, we perform a careful study of microphysical constraints in this scenario. We find that detectable modulations of the scalar power spectrum are commonplace in wellcontrolled examples, while resonant contributions to the bispectrum are undetectable in some classes of examples and detectable in others. We conclude that resonant contributions to the spectrum and bispectrum are a characteristic signature of axion monodromy inflation that, in favorable cases, could be detected in near-future experiments.arXiv:0907.2916v1 [hep-th]

Inflation and String Theory

“…Backreaction on the volume.-As mentioned above, a D3-brane with finite energy density backreacts on the overall compactification volume, which therefore depends on the brane position z α [218,320]: 36) where k(z α ,z α ) is the Kähler potential (5.14) and γ is a constant. In Appendix B of [218], the parameter γ was related to the stabilized value of the Kähler modulus,…”

“…In favorable cases, the embedding into quantum gravity can also entail small modifications of the theory that lead to additional observational signatures. For example, in axion monodromy inflation nonperturbative corrections introduce modulations of the power spectrum [36] and the bispectrum [37]. This is an example where the structure of the ultraviolet completion could potentially be inferred from correlated signatures.…”

“…In nonvacuum solutions containing these sources -or carrying the corresponding charges without any local sources -the compactification manifold is generally not Ricci-flat. For non-vacuum configurations with maximal symmetry in the noncompact spacetime, the product ansatz (3.36) is generalized to a 'warped' product: 36) where now g µν is the metric of a maximally symmetric spacetime, the warp factor A(y) is a function on X 6 , and the internal metric g mn is not necessarily Ricci-flat.…”

“…Such vacua are necessarily isolated: classical transitions from one to another require energy input. The string landscape is the collection of all consistent solutions of string theory that have four large spacetime dimensions 36 and do not have moduli. The expectation that string theory has a vast array of isolated solutions dates back to the early days of the theory [447,448], but detailed understanding of flux compactifications in recent years has brought the landscape into focus and has made explicit investigation possible.…”

“…Instead of computing all physically relevant quantities (a.k.a. 'observables') -such as gauge groups, coupling constants, and mass spectrain a small number of actual vacua, one can instead determine the statistical 36 The four-dimensional spacetime is often assumed to be maximally symmetric, i.e. de Sitter space, Minkowski space, or anti-de Sitter space.…”