Gravitational wave signatures of no-scale Supergravity in NANOGrav and beyond

Understand

In this Letter, we derive for the first time a characteristic three-peaked GW signal within the framework of no-scale Supergravity, being the low-energy limit of Superstring theory.

• We concentrate on the primordial gravitational wave (GW) spectrum induced due to second-order gravitational interactions by inflationary curvature perturbations as well as by isocurvature energy density perturbations of primordial black holes (PBHs) both amplified due to the presence of an early matter-dominated era (eMD) era before Big Bang Nucleosythesis (BBN).
• In particular, we work with inflection-point inflationary potentials naturally-realised within Wess-Zumino type no-scale Supergravity and giving rise to the formation of microscopic PBHs triggering an eMD era and evaporating before BBN.
• Remarkably, we obtain an abundant production of gravitational waves at the frequency ranges of $\mathrm{nHz}$, $\mathrm{Hz}$ and $\mathrm{kHz}$ and in strong agreement with Pulsar Time Array (PTA) GW data.