Is the CMB telling us that dark matter is weaker than weakly
  interacting?
  If moduli, or other long-lived heavy states, decay in the early universe in
part into light and feebly interacting particles (such as axions), these decay
products could account for the additional energy density in radiation that is
suggested by recent measurements of the CMB. These moduli decays will also,
however, alter the expansion history of the early universe, potentially
diluting the thermal relic abundance of dark matter. If this is the case, then
dark matter particles must annihilate with an even lower cross section than
required in the standard thermal scenario (sigma v < 3x10^-26 cm^3/s) if they
are to make up the observed density of dark matter. This possibility has
significant implications for direct and indirect searches for dark matter.
