We study the primordial non-Gaussinity predicted from simple models of
inflation with a linear potential and superimposed oscillations. This generic
form of the potential is predicted by the axion monodromy inflation model, that
has recently been proposed as a possible realization of chaotic inflation in
string theory, where the monodromy from wrapped branes extends the range of the
closed string axions to beyond the Planck scale. The superimposed oscillations
in the potential can lead to new signatures in the CMB spectrum and bispectrum.
In particular the bispectrum will have a new distinct shape. We calculate the
power spectrum and bispectrum of curvature perturbations in the model, as well
as make analytic estimates in various limiting cases. From the numerical
analysis we find that for a wide range of allowed parameters the model produces
a feature in the bispectrum with fnl ~ 50 or larger while the power spectrum is
almost featureless. This model is therefore an example of a string-inspired
inflationary model which is testable mainly through its non-Gaussian features.
Finally we provide a simple analytic fitting formula for the bispectrum which
is accurate to approximately 5% in all cases, and easily implementable in codes
designed to provide non-Gaussian templates for CMB analyses.Comment: 14 pages, 4 figures, added references, and a new figure with the
general shap
