Anisotropies in cosmological 21 cm background by oscillons/I-balls of ultra-light axion-like particle

Abstract

Abstract Ultra-light axion-like particle (ULAP) with mass m ∼ 10-22 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 ∼ 10 and affect the structure formation on a scale ∼ 𝒪(0.1) 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 𝒪(0.01 – 0.1).