Probing Small Scale Primordial Power Spectrum with 21cm Line Global Signal

TL;DR

This paper demonstrates that the global 21cm hydrogen line signal can effectively constrain the small-scale primordial power spectrum, providing insights into early universe fluctuations and structure formation.

Contribution

It introduces a method to use the 21cm line global signal to probe small-scale primordial fluctuations, accounting for astrophysical uncertainties.

Findings

Absorption trough position constrains small-scale fluctuations.

Astrophysical parameter uncertainties impact the constraints.

21cm line signals can differentiate primordial fluctuation amplitudes.

Abstract

We argue that the global signal of neutral hydrogen 21cm line can be a powerful probe of primordial power spectrum on small scales. Since the amplitude of small scale primordial fluctuations is important to determine the early structure formation and the timing when the sources of Lyman ${\alpha}$ photons are produced, they in turn affect the neutral hydrogen 21cm line signal. We show that the information of the position of the absorption trough can severely constrain the small scale amplitude of primordial fluctuations once astrophysical parameters relevant to the 21cm line signal are fixed. We also discuss how the uncertainties of astrophysical parameters affect the constraints.