Impact of EDGES 21cm Global Signal on Primordial Power Spectrum

TL;DR

This paper examines how the EDGES 21cm global signal constrains the primordial power spectrum's scale dependence, especially the running parameters, by linking early universe fluctuations to high-redshift 21cm observations.

Contribution

It introduces new constraints on the primordial power spectrum's running parameters using EDGES 21cm data, connecting cosmological models with astrophysical observations.

Findings

Certain parameter space of $oldsymbol{oldsymbol{oldsymbol{ extit{ extalpha}}_s}}$ and $oldsymbol{oldsymbol{oldsymbol{ extbeta}}_s}$ is disfavored by EDGES data.

The bounds on running parameters depend on astrophysical assumptions.

Some Planck-allowed parameters are incompatible with EDGES observations.

Abstract

We investigate the impact of the recent observation of the 21cm global signal by EDGES on primordial power spectrum, particularly focusing on the running parameters $\alpha_s$ and $ \beta_s$ which characterize the detailed scale dependence of the primordial spectrum. When primordial power spectrum is enhanced/suppressed on small scales, the structure formation proceeds faster/slower and changes the abundance of small size halos, which affects the sources of Lyman $\alpha$ radiation at high redshifts to alter the position of the absorption line. Recent observation of EDGES detected the 21cm absorption line at $z=17.2$ and this result also indicates that the brightness temperature is consistent with zero for $z \lesssim 14$ and $z \gtrsim 22$, which can exclude a scenario giving the absorption line at such redshifts. We argue that the bound on the running parameters can be obtained by requiring that the absorption line should not exceed observational bounds at such redshift ranges and found that some parameter space of $\alpha_s$ and $\beta_s$ allowed by Planck may be disfavored for some values of astrophysical parameters.