Impact of EDGES 21-cm global signal on the primordial power spectrum

Abstract

We investigate the impact of the recent observation of the 21-cm global signal by EDGES on the primordial power spectrum, particularly focusing on the running parameters ${\ensuremath{\alpha}}_{s}$ and ${\ensuremath{\beta}}_{s}$ which characterize the detailed scale dependence of the primordial spectrum. When the primordial power spectrum is enhanced or suppressed on small scales, the structure formation proceeds faster or slower and changes the abundance of small size halos, which affects the sources of Lyman $\ensuremath{\alpha}$ radiation at high redshifts to alter the position of the absorption line. A recent observation of EDGES detected the 21-cm absorption line at $z=17.2$, and this result also indicates that the brightness temperature is consistent with zero for $z\ensuremath{\lesssim}14$ and $z\ensuremath{\gtrsim}22$, 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 find that the parameter space of ${\ensuremath{\alpha}}_{s}$ and ${\ensuremath{\beta}}_{s}$ allowed by Planck may be disfavored for some values of astrophysical parameters.