On testing and extending the inflationary consistency relation for tensor modes

Understand

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.