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^-5 of closure density. Their characteristic wavelength depends upon the reheating temperature TRH: {λ}{~}(10⁴ cm)[(10¹⁴ GeV)/TRH]. If black holes are produced by bubble collisions, they will evaporate producing shorter-wavelength gravitons.