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

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 α s and β 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 α 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 14 and z 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 α s and β s allowed by Planck may be disfavored for some values of astrophysical parameters.

Probing the small-scale matter power spectrum with large-scale 21-cm data

“…Here, as in Refs. [22][23][24][25][26][27]39], we take advantage of this lower bound on the amount of Lyman-α photons to probe different dark-matter models. We will phrase the EDGES requirement in terms of the dimensionless coupling coefficient x α , which enters in the definition of the spin temperature (ignoring collisional coupling during cosmic dawn) as…”

“…Previous works have studied the effect of non-CDM models on the 21-cm signal [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. Those models typically suppress the matter power spectrum beyond some wavenumber k, delaying the onset of cosmic dawn.…”

Insight into primordial magnetic fields from 21-cm line observation with EDGES experiment

“…Note that the EDGES result is difficult to explain by the standard scenario: The amplitude of the absorption trough is almost twice as large as the maximal value expected in the standard cosmology. However, instead of giving an explanation on this anomaly, several authors have already applied the EDGES result to constrain some models: the Hawking evaporation of small primordial black holes (PBHs) (Clark et al 2018), the emission from the accretion discs around large PBHs (Hektor et al 2018), the decaying (Clark et al 2018;Mitridate & Podo 2018) or annihilating dark matter (Cheng et al 2018;D'Amico et al 2018), warm dark matter (Safarzadeh et al 2018), primordial power spectrum (Yoshiura et al 2018) and so on.…”

Probing small scale primordial power spectrum with 21cm line global signal

“…Since the amplitude of primordial fluctuations changes how structure formation proceeds, which affects the timing when Lyman α photon sources are switched on, then in turn, changes the structure of the global signal of neutral hydrogen 21cm line. Indeed, in our previous work [9], we have derived constraints on the so-called running parameters, which are commonly used to characterize higher order scale-dependence of primordial power spectrum and denoted as α s and β s , using this argument in the light of recent report from the EDGES low band result [10] where the absorption trough is detected at the frequency of ν = 78 MHz, corresponding to the redshift of z ∼ 17.2 #1 . In [9], we have shown that, by just using the information of the position (frequency) of the absorption trough, one can derive the constraint on α s and β s whose uncertainties are comparable to Planck #2 .…”

“…Indeed, in our previous work [9], we have derived constraints on the so-called running parameters, which are commonly used to characterize higher order scale-dependence of primordial power spectrum and denoted as α s and β s , using this argument in the light of recent report from the EDGES low band result [10] where the absorption trough is detected at the frequency of ν = 78 MHz, corresponding to the redshift of z ∼ 17.2 #1 . In [9], we have shown that, by just using the information of the position (frequency) of the absorption trough, one can derive the constraint on α s and β s whose uncertainties are comparable to Planck #2 . Here it should be noted that, although it is very common to parametrize primordial power spectrum with the spectral index n s and its runnings α s , β s , these parameters are usually defined at a reference wave number on large scale, which means that we extrapolate the power spectrum to smaller scales.…”