Search for strongly blue axion isocurvature

It is known that if the Peccei-Quinn symmetry-breaking field is displaced from its minimum during inflation, the axion isocurvature spectrum is generically strongly blue tilted with a break transition to a flat spectrum. We fit this spectrum (incorporated into the "vanilla" Lambda-CDM cosmological model) to the Planck and BOSS DR11 data to assess how much the existing data can accommodate the presence of axionic bluetilted isocurvature perturbations. We find that the preferred parameter region is consistent with all of the dark matter being composed of QCD axions in the context of inflationary cosmology with an expansion rate of order 10(8) GeV, the axion decay constant of order 10(13) GeV, and the initial misalignment angle of order unity. The data are consistent with there being no isocurvature perturbations at the level of just above one sigma. Intriguingly, isocurvature with a spectral break may at least partially explain the low-l vs high-l anomalies seen in the CMB data.