Current Dark Matter Annihilation Constraints from CMB and Low-Redshift Data

TL;DR

This work provides updated constraints on dark matter annihilation from a joint analysis of CMB data (Planck, WMAP9, ACT, SPT) combined with low-redshift probes, incorporating a refined energy-deposition framework. It introduces an updated universal energy-deposition curve $e(z)$ derived from $f_{\text{sys}}(z)$ for 41 channels and a corresponding $f_{\text{eff},\text{new}}$ mapping to $p_{\text{ann}} = f_{\text{eff},\text{new}} \frac{\langle\sigma v\rangle}{M_\chi}$, enabling robust constraints on redshift-dependent energy deposition. The results yield a 95% CL bound of $p_{\text{ann}} < 0.66\times10^{-6}$ m$^{3}$ s$^{-1}$ kg$^{-1}$ (all data) and exclude thermal DM with $M_\chi < 26$ GeV for $f_{\text{eff}}=1$ (or $M_\chi < 5$ GeV for $f_{\text{eff}}=0.2$), improving upon WMAP9 alone by roughly a factor of 2. These constraints intersect with interpretations of AMS-02/PAMELA and Fermi signals and with direct-detection hints, and future Planck data and CMB Stage IV experiments are expected to further tighten the limits by about another factor of ~2.

Abstract

Updated constraints on dark matter cross section and mass are presented combining CMB power spectrum measurements from Planck, WMAP9, ACT, and SPT as well as several low-redshift datasets (BAO, HST, supernovae). For the CMB datasets, we combine WMAP9 temperature and polarization data for l <= 431 with Planck temperature data for 432 < l < 2500, ACT and SPT data for l > 2500, and Planck CMB four-point lensing measurements. We allow for redshift-dependent energy deposition from dark matter annihilation by using a `universal' energy absorption curve. We also include an updated treatment of the excitation, heating, and ionization energy fractions, and provide updated deposition efficiency factors (f_eff) for 41 different dark matter models. Assuming perfect energy deposition (f_eff = 1) and a thermal cross section, dark matter masses below 26 GeV are excluded at the 2-sigma level. Assuming a more generic efficiency of f_eff = 0.2, thermal dark matter masses below 5 GeV are disfavored at the 2-sigma level. These limits are a factor of ~2 improvement over those from WMAP9 data alone. These current constraints probe, but do not exclude, dark matter as an explanation for reported anomalous indirect detection observations from AMS-02/PAMELA and the Fermi Gamma-ray Inner Galaxy data. They also probe relevant models that would explain anomalous direct detection events from CDMS, CRESST, CoGeNT, and DAMA, as originating from a generic thermal WIMP. Projected constraints from the full Planck release should improve the current limits by another factor of ~2, but will not definitely probe these signals. The proposed CMB Stage IV experiment will more decisively explore the relevant regions and improve upon the Planck constraints by another factor of ~2.

Figures (5)

• Figure 1: Universal energy deposition curve, $e(z)$, using approximations for the fraction of energy converted to heat, ionization, and excitation (dashed blue curve), and accounting for more accurate calculations of the energy fractions from Galli2013 (solid red curve).
• Figure 2: Fisher projected constraint obtained by including the range $500<l<5000$ and extending it cumulatively for each multipole below $l=500$. Experimental parameters are from Planck, an ACTpol-like experiment, and a cosmic variance limited experiment (see Table \ref{['tab:specs']}). Most of the leverage comes from $250<l<400$.
• Figure 4: 95% confidence limit contours for $n_s$ versus $p_\text{ann}$ and $\text{ln}(10^{10}A_s)$ versus $p_\text{ann}$, marginalized over the other parameters, for selected combinations of datasets.
• Figure 5: From top to bottom --- constraints on $p_{\text{ann}}$ from WMAP9 alone (pink) and from current data including WMAP9, Planck TT power spectrum and 4-point lensing signal, ACT, SPT, BAO, HST, and SN data (blue). Also shown are Fisher forecasts for the complete Planck temperature and polarization power spectra (green), for a proposed CMB Stage IV experiment ($50<l<4000$ combined with $l<50$ from Planck, shown in purple), and for a cosmic variance limited experiment (up to $l=4000$) (red). The dashed line shows the thermal cross section of $3\times 10^{-26}\text{cm}^3\text{s}^{-1}$ for $f_\text{eff}=1$. The dot-dashed line shows the thermal cross section multiplied by a typical energy deposition fraction of $f_\text{eff}=0.2$ (see Table \ref{['table:feffs']}).
• Figure 6: Current constraints are compared with dark matter model fits to data from other indirect and direct dark matter searches. The data from indirect searches include that from AMS-02, PAMELA, and Fermi, and the data from direct searches include that from CDMS, CoGeNT, CRESST, and DAMA. The lighter shaded direct detection region allows for p-wave annihilations, and the dashed vertical lines for the indirect detection regions allow for p-wave annihilations for non-thermally produced dark matter.