Updated CMB constraints on dark matter annihilation cross sections

The injection of secondary particles produced by dark matter (DM) annihilation at redshift $100\lesssim z\lesssim 1000$ affects the process of recombination, leaving an imprint on cosmic microwave background (CMB) anisotropies. Here we provide a new assessment of the constraints set by cosmic microwave background data on the mass and self-annihilation cross section of DM particles. Our new analysis includes the most recent WMAP (7-year) and ACT data, as well as an improved treatment of the time-dependent coupling between the DM annihilation energy with the thermal gas. We show, in particular, that the improved measurement of the polarization signal places already stringent constraints on light DM particles, ruling out “thermal” WIMPs with mass $m_{\chi }\lesssim 10\mathrm{GeV}$ annihilating into electrons and WIMPs with mass $m_{\chi }\lesssim 4\mathrm{GeV}$ annihilating into muons.

Figure 1

Constraints on the cross section $⟨\sigma v⟩$ in the function of the mass, obtained using a variable $f(z)$ for particles annihilating in muons ($x$ signs) and in electrons (diamonds) using WMAP7 data (red) and $\mathrm{WMAP}7+\mathrm{ACT}$ data (black) at 95% C.L. The exclusion shaded areas are obtained for the interpolation of the $\mathrm{WMAP}7+\mathrm{ACT}$ data points for muons (dark shading) and electrons (light shading). The black solid line indicates the thermal cross-section $⟨\sigma v⟩=3\times {10}^{-26}{\mathrm{cm}}^3/\mathrm{s}$.