  The high positron production rate required to explain the flux of 511 keV
gamma rays from the galactic center has inspired many models in which dark
matter creates positrons. These models include the annihilation of light dark
matter and scattering of dark matter with excited states (exciting dark
matter). We show that existing cosmic microwave background data robustly
constrains such models when the annihilation or scattering cross section is not
velocity suppressed depending on the model of the galactic dark matter halo.
Upcoming data from the Planck mission can exclude the fiducial Via Lactea II
halo model, which also provides a good fit to the 511 keV morphology. We
additionally find combined constraints on exciting dark matter scattering and
annihilation and update constraints on the lifetimes of dark matter excited
states. Finally, we apply constraints to models of dark matter decay in which
produced positrons fall into the galactic center and produce the 511 keV signal
on their annihilation, demonstrating that most of the parameter space of
interest is ruled out.
