Phase decoherence of gravitational wave backgrounds
  Metric perturbations affect the phase of gravitational waves as they
propagate through the inhomogeneous universe. This effect causes Stochastic
Gravitational Wave Backgrounds (SGWBs) to lose any phase coherence that may
have been present at emission or horizon entry. We show that, for a standard
cosmological model, this implies complete loss of coherence above frequencies
$f \sim 10^{-12}$ Hz. The result is that any attempts to map SGWBs using
phase-coherent methods have no foreseeable applications. Incoherent methods
that solve directly for the intensity of the SGWBs are the only methods that
can reconstruct the angular dependence of any SGWB.
