Fossilized Gravitational Wave Relic and Primordial Clocks
  If long wavelength primordial tensor modes are coupled to short wavelength
scalar modes, the scalar curvature two-point function will have an off-diagonal
component. This `fossil' remnant is a signature of a mode coupling that cannot
be achieved in single clock inflation. Any constraint on its presence allows a
cross check of the relationship between the dynamical generation of the
fluctuations and the evolution of the inflationary background. We use the
example of non-Bunch Davies initial states for the tensor and scalar modes to
demonstrate that physically reasonable fossils, consistent with current data,
can be observable in the near future. We illustrate how the fossil off-diagonal
power spectrum is a complementary probe to the squeezed limit bispectra of the
scalar and tensor sectors individually. We also quantify the relation between
the observable signal and the squeezed limit bispectrum for a general
scalar-scalar-fossil coupling, and note the effect of superhorizon tensor modes
on the anisotropy in scalar modes.
