On testing and extending the inflationary consistency relation for
  tensor modes
  If observations confirm BICEP2's claim of a tensor-scalar ratio $r\approx
0.2$ on CMB scales, then the inflationary consistency relation $n_{t}=-r/8$
predicts a small negative value for the tensor spectral index $n_t$. We show
that future CMB polarization experiments should be able to confirm this
prediction at several sigma. We also show how to properly extend the
consistency relation to solar system scales, where the primordial gravitational
wave density $\Omega_{gw}$ could be measured by proposed experiments such as
the Big Bang Observer. This would provide a far more stringent test of the
consistency relation and access much more detailed information about the early
universe.
