Kavli Affiliate: Wayne Hu
| First 5 Authors: Rayne Liu, Wayne Hu, Daniel Grin, ,
| Summary:
Ultralight axions (ULAs) with masses $10^{-33} lesssim m/{rm eV} lesssim
10^{-12}$ are well motivated in string-inspired models and can be part or all
of the dark energy or the dark matter in this range. Since the ULA field
oscillates at a frequency $m$ that can be much larger than the expansion rate
$H$, accurate and efficient calculation of cosmological observables requires an
effective time averaged treatment. While these are well established for $mgg
10 H_{rm eq}$, the Hubble rate at matter radiation equality, here we extend
and develop these techniques to cover the mass range $10^{-33} lesssim m/{rm
eV} lesssim 10^{-18}$. We implement this technique in a full cosmological
Boltzmann code ($mathrm{AxiECAMB}$) with numerical precision sufficiently
accurate for current and next-generation cosmic microwave background as well as
large-scale structure data analysis. New effects including the time averaging
of metric perturbations and hydrostatic equilibrium of the effective fluid
result in many orders of magnitude improvements for power spectra accuracy over
some previous treatments such as $mathrm{AxionCAMB}$ in some extreme regions
of parameter space and order unity changes of the ULA effects near $Lambda$CDM
models. These improvements may impact the model parameters that resolve various
tensions in $Lambda$CDM at a comparable level.
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