Cosmic Microwave Background Probes Models of Inflation
  Inflation creates both scalar (density) and tensor (gravity wave) metric perturbations. We find that the tensor mode contribution to the CMB anisotropy on large-angular scales can only exceed that of the scalar mode in models where the spectrum of perturbations deviates significantly from scale invariance (e.g., extended and power-law inflation models and extreme versions of chaotic inflation). If the tensor mode dominates at large-angular scales, then the value of $\Delta T/T$ predicted on $1^\circ$ is less than if the scalar mode dominates, and, for cold dark matter models, $b>1$ can be made consistent with the COBE DMR results. 
R.L. Davis, H.M. Hodges, G.F. Smoot, P.J. Steinhardt, M.S. Turner