Double peaks of gravitational wave spectrum induced from inflection point inflation

Understand

We investigate the possibility to induce double peaks of gravitational wave(GW) spectrum from primordial scalar perturbations in inflationary models with three inflection points.Where the inflection points can be generated from a polynomial potential or generated from Higgs like $\phi^4$ potential with the running of quartic coupling.In such models, the inflection point at large scales predicts the scalar spectral index and tensor-to-scalar ratio consistent with current CMB constraints, and the other two inflection points generate two large peaks in the scalar power spectrum at small scales, which can induce GWs with double peaks energy spectrum.

• We find that for some choices parameters the double peaks spectrum can be detected by future GW detectors, and one of the peaks around $f\simeq10^{-9}\sim10^{-8}$Hz can also explain the recent NANOGrav signal.
• Moreover, the peaks of power spectrum allow for the generation of primordial black holes, which account for a significant fraction of dark matter.