Cosmological Search for Ultra-Light Axions
Proceedings of the 11th Patras Workshop on Axions, WIMPs and WISPs, PATRAS 2015 (2015) 3-10
Authors:
D Grin, R Hlozek, DJE Marsh, PG Ferreira
Abstract:
Ultralight axions (ULAs) with masses in the range 10-33 eV ma 10-18 eV (motivated by string theory) might contribute to the dark-matter or dark-energy density of the Universe. ULAs would suppress the growth of structure on small scales and change the shape of the cosmic microwave background (CMB) anisotropy power spectra. In this work, we compute cosmological observables over the full ULA mass range and then use them to search for evidence of ULAs using CMB temperature data from the Planck satellite, large-scale CMB polarization data from Wilkinson Microwave Anisotropy Probe (WMAP), smallerscale CMB experiments, as well as the WiggleZ galaxy-redshift survey. In the mass range 10-32 eV ma 10-25.5 eV, the ULA relic-density must obey the constraint ah2 0.006 at 95%-confidence. For ma & 10-24 eV, ULAs are indistinguishable from standard cold dark matter on the length scales probed while for ma . 10-32 eV, ULAs are allowed to compose a significant fraction of the dark energy. If primordial gravitational waves are detected, limits to the primordial isocurvature fraction will put severe constraints on ULA dark matter. In the future, weak-lensing measurements of the CMB will yield even more powerful probes of the ULA hypothesis.
