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 CMB 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 GeV .