Figure 1

The spectrum of relic scalar gravitational waves in inflationary models is flat over a wide range of frequencies. The horizontal axis is ${log}_{10}$ of frequency, in Hz. The vertical axis is ${log}_{10}{\Omega }_{\mathrm{gsw}}$. The inflationary spectrum rises quickly at low frequencies (wave which reentered the Hubble sphere after the Universe became matter-dominated) and falls off above the (appropriately redshifted) frequency scale $f_{\max }$ associated with the fastest characteristic time of the phase transition at the end of inflation. The amplitude of the flat region depends only on the energy density during the inflationary stage; we have chosen the largest amplitude consistent with the WMAP constraints on scalar perturbations. This means that, at LIGO and LISA frequencies, ${\Omega }_{\mathrm{sgw}}<2.3·{10}^{-12}$.Reuse & Permissions