This website can be used to calculate the relic density of dark
matter, and the annihilation cross section in the local halo and in
the limit of low velocity, for a simple example model with Sommerfeld
enhancement and two nearly degenerate dark matter states (detailed in
). It can also be used to estimate the relic fraction of dark
matter in the excited state, x_e, prior to decay (however, see the
 D. P. Finkbeiner, L. Goodenough, T. R. Slatyer, M. Vogelsberger and N. Weiner, "Consistent Scenarios for Cosmic-Ray Excesses from Sommerfeld-Enhanced Dark Matter Annihilation".
 T. R. Slatyer, "The Sommerfeld enhancement for dark matter with an excited state", arXiv:0910.5713.