Exploring the Co-SIMP dark matter model using the 21-cm signal from dark ages

TL;DR

This work tests the co-SIMP dark matter model using the redshifted 21-cm signal from the dark ages. By parameterizing the DM–IGM coupling with $C_{\rm int}$, the authors compute the global brightness temperature $\overline{T}_{21}$ and the 21-cm power spectrum, showing that stronger co-SIMP interactions deepen and shift the absorption trough to higher redshifts, while later epochs see a suppression due to altered collisional coupling. Fisher forecasts and signal-to-noise estimates for global-signal and interferometric measurements across multiple experimental configurations indicate that upcoming space-based and lunar 21-cm experiments could distinguish co-SIMP scenarios from $\Lambda$CDM with significant significance (up to $\sim$10–100$\,\sigma$ in favorable cases). The results underscore the potential of 21-cm cosmology as a powerful probe of DM microphysics and motivate dedicated dark-ages experiments. Key quantitative findings include a CDM trough at $z\approx85.6$ with $\overline{T}_{21}\approx-\!40.6$ mK, deepened troughs for $C_{\rm int}=1$–$3$ up to $-78.3$ mK at $z\approx87$, and substantial PS detectability enhancements in optimal configurations.

Abstract

The redshifted 21-cm signal from the dark ages offers a powerful probe of cosmological models and the underlying dark matter microphysics. We investigate deviations from the standard $Λ$CDM prediction, an absorption trough of approximately $-40.6\,\mathrm{mK}$ at redshift $z \simeq 85.6$, in the context of co-SIMP dark matter. The strength of co-SIMP interactions, quantified by the parameter $C_{\rm int}$, enhances the absorption depth and shifts the trough to higher redshifts. For example, a model with $C_{\rm int}=1.0$ produces a minimum brightness temperature of $-50.6\,\mathrm{mK}$ at $z \simeq 86.2$. The 21-cm power spectrum increases with $C_{\rm int}$ in addition to the global signal. We assess the detectability of these signatures using signal-to-noise ratio (SNR) and Fisher matrix forecasts. The maximum SNR reaches $\sim 15.7$ for $C_{\rm int}=1.0$ for the global signal. Fisher forecast for $1,000$ hours of integration time shows that this model can be distinguished from a null-signal at $4.3σ$ and from the $Λ$CDM model case at $1.6 σ$, with order-of-magnitude improvements for 100,000 hours of integration. For the 21-cm power spectrum, our forecasts reveal complementary trends; with a modest setup (collecting area of $5\,\mathrm{km}^2$ and 1,000 hours of integration time), the $C_{\rm int}=1.0$ model can be detected at $4.63σ$ and differentiated from the standard scenario at $1.78 σ$. These findings highlight the potential of the 21-cm cosmology to probe the properties of dark matter and demonstrate that upcoming dark ages experiments, particularly space-based and lunar observations, can offer a promising avenue to test co-SIMP models.

Figures (10)

• Figure 1: Schematic diagram for $2\rightarrow 3$ co-SIMP interaction process.
• Figure 2: The global signal shows an overall depletion relative to the $\Lambda$CDM scenario across entire redshift range. However, for $z \geq 50$, the magnitude of depletion increases with increasing $C_{\rm int}$, whereas for $z < 50$, the trend reverses, leading to a reduction in depletion with higher $C_{\rm int}$.
• Figure 3: The 21-cm power spectra for the three different values of $C_{\rm int}$ of co-SIMP model, compared with CDM. Left panel is for $z=60$, while right panel is for $z=40$.
• Figure 4: The redshift evolution of 21-cm power spectra for the co-SIMP models for three different values of $C_{\rm int}$, compared with the CDM model. The power spectra are plotted at four values of $k$ (Mpc$^{-1}$).For $z\gtrsim 50$, the power spectrum increases with stronger DM interactions, whereas the trend reverses for $z<50$.
• Figure 5: The SNR for the global 21-cm signal measurements as a function $z$, considering various $C_{\rm int}$, for $t_{\rm int}=10,000$ hours and $\Delta \nu=5$ MHz. The black dashed line represents the CDM scenario. Co-SIMP interaction enhances the SNR for $z\gtrsim 50$, however, the trend reverses for $z<50$.