Calculation of the Ostriker-Vishniac Effect for Cosmological Models with Ulta-light Axions
Abstract
We extend the formalism for computing the Ostriker-Vishniac effect which probes density-velocity correlations at small angular scales to cosmological models with scale-dependent growth arising in the context of ultra-light axions (ULAs). Such scalar particles with masses in the range 10-33-20 eV are motivated in string theory and were originally proposed to solve the CP violation problem. The axion field initially evolves slowly in time and has equation of state w ≈ -1. Once m_a is approximately greater or equal to 3H the field starts oscillating rapidly and the effective equation of state is weff ≈ 0, leading to the ULA number density approximately diluting with matter. The oscillatory nature of the axion field gives rise to a scale-dependent perturbation sound speed, leading perturbations on small scales to oscillate rather than grow, suppressing the growth of structure. Using the angular power spectrum of the Ostriker-Vishniac effect one would be able to probe the growth of structure during the period of reionization, sharpening the constraints on axion abundance already derived from primary CMB anisotropies and large-scale structure surveys. We present numerical calculations showing how the modifications to the growth of structure as a function of time and scale effect the Ostriker-Vishniac angular power spectrum in the presence of ULAs.
- Publication:
-
American Astronomical Society Meeting Abstracts #233
- Pub Date:
- January 2019
- Bibcode:
- 2019AAS...23334915F