I summarize the recent advances in determining the effects of self-annihilating WIMP dark matter on the modification of the recombination history , at times earlier than the formation of astrophysical objects .
Depending on mass and self-annihilation cross section , WIMP DM can reproduce sizable amounts of the total free electron abundance at z \buildrel > \over { { } _ { \sim } } 6 ; as known , this affects the CMB temperature and polarization correlation spectra , and can be used to place stringent bounds in the particle mass vs cross-section plane .
WMAP5 data already strongly disfavor the region capable to explain the recent cosmic positron and electrons anomalies in terms of DM annihilation , whereas in principle the Planck mission has the potential to see a signal produced by a candidate laying in that region , or from WIMPs with thermal annihilation cross-sections \langle \sigma v \rangle \sim 3 \times 10 ^ { -26 } cm ^ { 3 } /s and masses with values m _ { \chi } \buildrel < \over { { } _ { \sim } } 50 GeV/c ^ { 2 } .