Speaker
Andreas Pargner
(Karlsruhe Insitute of Technology)
Description
Based on the work published in arXiv: 1903.06194. In collaboration with M. Feix (Univ. Heidelberg), J. Frank (KIT), R. Reischke (IIT, Haifa), B.M. Schaefer (Univ. Heidelberg), T. Schwetz (KIT).
We assume that dark matter is comprised of axion-like particles (ALPs) generated by
the realignment mechanism in the post-inflationary scenario. This leads to isocurvature
fluctuations with an amplitude of order one for scales comparable to the horizon at the
time when the ALP field starts oscillating. The power spectrum of these fluctuations
is flat for small wave numbers, extending to scales relevant for cosmological observables.
Denoting the relative isocurvature amplitude at $k_* = 0.05$~Mpc$^{-1}$ by $f_{\rm iso}$,
Planck observations of the cosmic microwave background (CMB) yield $f_{\rm iso} < 0.31$
at the $2\sigma$-level. This excludes the hypothesis of post-inflationary ALP dark matter
with masses $m_a < 10^{-20}$-$10^{-16}$~eV, where the range is due to details of the ALP
mass-temperature dependence. Future CMB stage IV and 21-cm intensity mapping experiments
may improve these limits by 1-2 orders of magnitude in $m_{a}$.
Primary author
Andreas Pargner
(Karlsruhe Insitute of Technology)
