Constraints on primordial density perturbations from induced
  gravitational waves
  We consider the stochastic background of gravitational waves produced during
the radiation-dominated hot big bang as a constraint on the primordial density
perturbation on comoving length scales much smaller than those directly probed
by the cosmic microwave background or large-scale structure. We place weak
upper bounds on the primordial density perturbation from current data. Future
detectors such as BBO and DECIGO will place much stronger constraints on the
primordial density perturbation on small scales.
