Relic gravitational waves and extended inflation

In extended inflation, a new version of inflation where the transition from an inflationary to a radiation-dominated Universe is accomplished by bubble nucleation, bubble collisions supply a potent—and potentially detectable—source of gravitational waves. The energy density in relic gravitons from bubble collisions is expected to be about ${10}^{\mathrm{-}5}$ of closure density. Their characteristic wavelength depends upon the reheating temperature ${\mathit{T}}_{\mathrm{R}\mathrm{H}:}$ λ∼(${10}^4$ cm)[(${10}^{14}$ GeV)/${\mathit{T}}_{\mathrm{RH}}$]. If black holes are produced by bubble collisions, they will evaporate producing shorter-wavelength gravitons.