Induced gravitational waves from the cosmic coincidence

TL;DR

This paper explores the spectrum of induced gravitational waves from ultra-slow-roll inflation, linking it to primordial black hole dark matter and baryogenesis, and discusses how upcoming detectors can test these models.

Contribution

It provides a novel analysis of the induced GW spectrum within USR inflation, connecting it to the cosmic coincidence and observational prospects for PBH dark matter.

Findings

Bounds on spectral index $n_{UV}$ for high-frequency GW spectrum

Potential detectability of USR inflation signatures by upcoming GW observatories

Link between baryogenesis, PBH dark matter, and GW signals

Abstract

The induced gravitational wave (GW) background from enhanced primordial scalar perturbations is one of the most promising observational consequences of primordial black hole (PBH) formation from inflation. We investigate the induced GW spectrum $\Omega_{\textrm{IGW}}$ from single-field inflation in the general ultra-slow-roll (USR) framework, restricting the peak frequency band to be inside $10^{-3}$-$1$ Hz and saturating PBH abundance to comprise all dark matter (DM) in the ultralight asteroid-mass window. By invoking successful baryogenesis driven by USR inflation, we verify the viable parameter space for the specific density ratio between baryons and PBH DM observed today, the so-called "cosmic coincidence." We show that the cosmic coincidence requirement bounds the spectral index $n_{\rm UV}$ in the high frequency limit, $\Omega_{\textrm{IGW}}(f\gg 1)\propto f^{-2n_{\rm UV}}$, into $0 < n_{\rm UV} < 1$, which implies that baryogenesis triggered by USR inflation for PBHs in the mass range of $10^{-16}$-$10^{-12} M_\odot$ can be tested by upcoming Advanced LIGO and Virgo data and next generation experiments such as LISA, Einstein Telescope, TianQin and DECIGO.