COBE, Inflation, and Light Scalars
  Comparison of theobservedanisotropy with that predicted iadiabaticDM models suggest that much of thserved signal may be due to long wavelenh gravitational waves. In inflationary models this requires the generation of tensor fluctuations to be at least comparable to scalar density fltuations. This i is feasible, but depends sensitively on the inflaton potential. Alternatively, isocurvature quantum fluctuations in an axion-like field could produce a quadrupole anisotropy proportional to the gravitational wave anisotropy,k independent of the inflaton potential. These could also produce large scale structure with more power on larger scales than their adiabatic counterparts. 
Lawrence M. Krauss