Anisotropies in Cosmological 21 cm Background by Oscillons/I-balls of
  Ultra-light Axion-like Particle
  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 $\mathcal{O}(0.01 \text{--} 0.1)$.
