A Bump in the Blue Axion Isocurvature Spectrum
  Blue axion isocurvature perturbations are both theoretically well-motivated
and interesting from a detectability perspective. These power spectra
generically have a break from the blue region to a flat region. Previous
investigations of the power spectra were analytic, which left a gap in the
predicted spectrum in the break region due to the non-applicability of the used
analytic techniques. We therefore compute the isocurvature spectrum numerically
for an explicit supersymmetric axion model. We find a bump that enhances the
isocurvature signal for this class of scenarios. A fitting function of three
parameters is constructed that fits the spectrum well for the particular axion
model we study. This fitting function should be useful for blue isocurvature
signal hunting in data and making experimental sensitivity forecasts.
