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

TL;DR

This paper explores how ultra-light axion-like particles forming oscillons can influence 21 cm background anisotropies, potentially observable by future radio telescopes like SKA, offering insights into small-scale structure formation.

Contribution

It introduces the impact of ULAP-induced oscillons on 21 cm anisotropies and assesses their detectability with upcoming observations, linking particle physics to cosmological signals.

Findings

Oscillons can amplify 21 cm anisotropies on small scales.

Future observations like SKA could detect ULAP effects if their abundance is sufficient.

ULAP oscillons influence structure formation at redshifts up to z~10.

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 $\mathcal{O}(0.01 \text{--} 0.1)$.