CMB Constraints on Sommerfeld-Enhanced Dark Matter

          @misc{ pirsa_PIRSA:09060039,
            doi = {10.48660/09060039},
            url = {https://pirsa.org/09060039},
            author = {Slatyer, Tracy},
            keywords = {Particle Physics, Cosmology},
            language = {en},
            title = {CMB Constraints on Sommerfeld-Enhanced Dark Matter},
            publisher = {Perimeter Institute},
            year = {2009},
            month = {jun},
            note = {PIRSA:09060039 see, \url{https://pirsa.org}}
          }
          

Abstract

Dark matter (DM) annihilation around the redshift of last scattering can alter the recombination history of the universe, broaden the last scattering surface, and influence the observed temperature and polarization fluctuations of the cosmic microwave background (CMB). Unlike other indirect astrophysical signals of DM annihilation, these CMB signatures are free of the significant uncertainties inherent in modeling galactic physics, and provide an independent method to test and constrain models of dark matter. Recently measured anomalous excesses of 10-1000 GeV electron and positron cosmic rays have motivated DM models with large annihilation cross sections when the relative velocity of the annihilating particles is low. We have calculated in detail the efficiency with which energy from DM annihilation is deposited into the photon-baryon plasma around the redshift of last scattering, for an array of annihilation channels, allowing precise predictions of the effect of DM annihilation on the CMB. I will discuss CMB constraints for specific annihilation channels, which can strongly limit the allowed parameter space for DM models fitting the excesses measured by PAMELA and/or Fermi. I will also describe degeneracies between the effect of DM annihilation and changes to the cosmological parameters, and their implications. In particular, DM annihilation could alter the apparent value of the scalar spectral index n_s as measured by WMAP.