# Small-scale structure and 21cm fluctuations by primordial black holes

## TL;DR

This paper investigates how primordial black holes influence early small-scale structure formation and 21cm signals, revealing that even a tiny PBH fraction significantly alters halo populations and could be detected by future radio surveys.

## Contribution

It introduces a calculation of halo mass function and power spectrum considering PBH Poisson fluctuations and predicts observable 21cm signatures at high redshifts.

## Key findings

- Small PBH fractions significantly modify small halo abundance.
- PBHs can produce detectable 21cm signals at high redshifts.
- Future experiments like SKA can constrain PBH abundance.

## Abstract

We discuss early structure formation of small scales sourced by primordial black holes (PBHs) which constitute a small part of present cold dark matter component. We calculate the mass function and power spectrum of haloes originated from the Poisson fluctuations of PBH number and show that the number of small haloes is significantly modified in the presence of PBHs even if their fraction accounts for only $10^{-4}$--$10^{-3}$ of total dark matter abundance. We then compute the subsequent 21cm signature from those haloes. We find that PBHs can provide major contributions at high redshifts within the detectability of future experiments such as Square Kilometer Array, and provide a forecast constraint on the PBH fraction.