A novel mechanism of inflation is proposed where, starting only from a preexisting de Sitter background, no scalar fields are present, and density perturbations arise from the nonlinear evolution of gravitational waves, which unavoidably arise as quantum vacuum oscillations of the metric. This model-free picture of the early Universe gives concrete predictions that can be tested against cosmological observations.

…In this framework, inflation is driven by a de Sitter space time, where tensor metric fluctuations (i.e., gravitational waves) naturally arise from quantum vacuum oscillations, and scalar fluctuations are generated via second-order tensor effects. We compute the power spectrum of such scalar fluctuations and show it to be consistent with near scale invariance…