Anisotropies in Cosmological 21 cm Background by Oscillons/I-balls of Ultra-light Axion-like Particle

Abstract

Ultra-light axion-like particle (ULAP) with mass $m\sim 10^{-22}\mathrm{eV}$ has recently been attracting attention as a possible solution to the small-scale crisis. ULAP forms quasi-stable objects called oscillons/I-balls, which can survive up to a redshift $z\sim 10$ and affect the structure formation on a scale $\sim \mathcal{O}(0.1)\mathrm{Mpc}$ by amplifying the density fluctuations. We study the effect of oscillons on 21~cm anisotropies caused by neutral hydrogen in minihalos. It is found that this effect can be observed in a wide mass range by future observations such as Square Kilometer Array~(SKA) if the fraction of ULAP to the total dark matter density is $\mathcal{O}(0.01\text{–}0.1)$.

Comments: 18 pages, 7 figures