Abstract: |
Current measurements of cosmic structure provide unprecedented constraints on the initial density field. A sharply blue-tilted isocurvature component of the density fluctuations, indicative of an evolving mass during inflation, is accessible to CMB and large-scale structure observations. I discuss an axionic spectator field model whose power spectrum has a characteristic bump associated with a transition from a blue to a flat spectrum. Through careful numerical analysis I construct a fitting function capturing the essential features of this power spectrum component. Employing Time-RG cosmological perturbation theory, I develop a phenomenological treatment of the galaxy power spectrum sensitive to scale-dependent corrections to the initial power spectrum as well as to late-time scale-dependent growth due, for example, to massive neutrinos. Finally, I combine these theoretical tools in order to constrain isocurvature using the Planck and BOSS surveys, which prefer a strongly blue-tilted isocurvature component at the two sigma level, and I consider the phenomenological implications of these results. |