We study the interaction between dark sectors by considering the momentum transfer caused by the dark matter scattering elastically within the dark energy fluid .
Describing the dark scattering analogy to the Thomson scattering which couples baryons and photons , we examine the impact of the dark scattering in CMB observations .
Performing global fitting with the latest observational data , we find that for a dark energy equation of state w < -1 , the CMB gives tight constraints on dark matter-dark energy elastic scattering .
Assuming a dark matter particle of proton mass , we derive an elastic scattering cross section of \sigma _ { D } < 3.295 \times 10 ^ { -10 } \sigma _ { T } where \sigma _ { T } is the cross section of Thomson scattering .
For w > -1 , however , the constraints are poor .
For w = -1 , \sigma _ { D } can formally take any value .