Sensitivity of the Global 21-cm Signal to Dark Matter-Baryon Scattering

Abstract

With current and upcoming experiments on the horizon, the global 21-cm signal can open up new avenues for probing dark matter (DM) physics at redshifts that are otherwise inaccessible to other observables. This work investigates the effects of elastic scattering between DM and baryons on the global 21-cm signal in two distinct interacting DM (IDM) models: Coulomb-like and velocity-independent interactions. Our analysis incorporates key astrophysical parameters essential for accurately modeling the global signal, including star formation efficiency, escape fraction of ionizing photons, normalization of the X-ray luminosity, the number of Lyman-Werner photons emitted per stellar baryon, the minimum virial temperature of star-forming halos, as well as the IDM particle mass and cross section. We perform a Fisher analysis to forecast the sensitivity of four global 21-cm signal experimental scenarios as probes of DM-baryon scattering. We find that global signal experiments, even at the sensitivity of the current facilities such as EDGES and SARAS3, could improve existing cosmological and astrophysical constraints on DM-baryon scattering. Our results also highlight the degeneracies among the DM-baryon interaction cross section and astrophysical quantities. In particular, degeneracies between the IDM cross section and two astrophysical parameters, the minimum virial temperature, and Lyman-Werner photon production, can significantly impact the DM interaction inference. Conversely, the velocity-independent cross section is found to be insensitive to uncertainties in the X-ray luminosity. These findings underscore the necessity of accurately characterizing the uncertainties in astrophysical parameters to leverage the full potential of the 21-cm global signal experiments in probing IDM physics.

Figures (6)

• Figure 1: The Global 21-cm signal as a function of frequency in IDM models with $n=0$ (left-hand panel) and $n=-4$ (right-hand panel), for DM particle mass of $1$ GeV, are shown. The error bars represents the rms noise of the EDGES experiment. The color scheme captures the change in the signal as a function of the interaction cross section.
• Figure 2: The Radiometer and RMS (white) noise for EDGES and SARAS3 experiments are shown in solid and dashed lines, respectively. Radiometer noise levels are calculated using the specifications listed in Table \ref{['tab:experiment_specs']}, while the white noise levels are calculated using the smoothed noise reported by the respective experiment edges_naturesingh2022detection.
• Figure 3: Forecasts on astrophysical parameters and the cross section of interactions for the velocity-independent cross section IDM model with a fixed DM mass of $10$ MeV are presented. These forecasts are obtained for an EDGES-like experiment, using the RMS noise model for the input covariance matrix. The two-dimensional contours represent the $68\%$ and $95\%$ confidence regions of the posterior probability distribution, shown by the dotted and solid black curves, respectively, while the top panel of each represents the marginalized posterior distributions for the corresponding parameters. The gray lines correspond to the fiducial values of each parameter.
• Figure 4: Similar to the triangle plot in Fig. \ref{['plt:n0_tri_global']} for $n = 0$, we present the forecasts on astrophysical parameters and $\mathrm{\sigma}_{0}$ for the Coulomb-like IDM model with a fixed DM mass of $10$ MeV. These forecasts are obtained for an EDGES-like experiment, using the RMS noise model for the input covariance matrix. The two-dimensional contours represent the $68\%$ and $95\%$ confidence regions of the posterior probability distribution, shown by the dotted and solid black curves, respectively, while the top panel of each column represents the marginalized posterior distributions for the corresponding parameters. The gray lines correspond to the fiducial values of each parameter.
• Figure 5: The 95% confidence level upper limit forecasts on $\log_{10}(\sigma_{0}/\mathrm{cm}^2)$ as a function of IDM mass are shown for a velocity-independent cross section IDM model ($n=0$) and four different experimental scenarios. The previous bounds from CMB nguyen2021observational and Milky Way satellite abundance maamari2021bounds are also plotted for the comparison. While a SARAS-like experiment shows results comparable to the current best bound, the other three experimental scenarios predict stronger forecasts.