Name: Thomas Tram Bülow
 Institution: Institute of Physics and Astronomy, Aarhus University
 Title: Properties of Sommerfeld Enhanced DM
 Key Words: Dark Matter, Sommerfeld Enhancement, Freeze Out, CMB Spectrum distortions
 Abstract: In the last few years there has been some interest in WIMP Dark Matter models featuring a
velocity dependent cross section through the Sommerfeld enhancement mechanism. The idea is to
have light bosons mediate a force between the WIMPs, which gives rise to a Yukawa-potential. In
the first part of this article, we analyse the Sommerfeld enhancement in detail. We find analytic
expressions for the boost factor for three different model-potentials, Coulomb, the spherical well and
the spherical cone well and compare with the numerical solution in the Yukawa case. In the second
part of the article, we do a detailed computation of the Dark Matter relic density for models having
Sommerfeld-enhancement by solving the Boltzmann equation numerically. As an application we
compare the expected distortions of the CMB blackbody spectrum to the bounds set by FIRAS.