Abstract
We discuss a possible connection between the recent NANOGrav results and the primordial black holes (PBHs) for the LIGO-Virgo events. In particular, we focus on the axionlike curvaton model, which provides a sizable amount of PBHs and gravitational waves (GWs) induced by scalar perturbations around the NANOGrav frequency range. The inevitable non-Gaussianity of this model suppresses the induced GWs associated with PBHs for the LIGO-Virgo events to be compatible with the NANOGrav results. We show that the axionlike curvaton model can account for PBHs for the LIGO-Virgo events and the NANOGrav results simultaneously.
Highlights
We focus on the axionlike curvaton model, which provides a sizable amount of primordial black holes (PBHs) and gravitational waves (GWs) induced by scalar perturbations around the NANOGrav frequency range
We show that the axionlike curvaton model can account for PBHs for the LIGO-Virgo events and the NANOGrav results simultaneously
Induced gravitational waves.—Here we briefly review the fundamental equations of GWs induced by scalar perturbations
Summary
4 9 c; ð6Þ where H is the Hubble parameter during the inflation, c is the coefficient coming from the supergravity effect, and f is a symmetry breaking scale. We assume that c is of Oð1Þ and the initial value of φ is much larger than f, which makes φ roll down the potential to the minimum f during inflation. Once φ reaches the minimum f, the curvaton is given by σ ≡ θf. To the QCD axion, we assume that a certain nonperturbative dynamics generates a mass to the curvaton at some point after reheating. ; ð2Þ where Λ is the scale of the nonperturbative dynamics and the curvaton mass is obtained from mσ ≡ Λ2=f. In the axionlike curvaton model, the power spectrum of curvature perturbations on small scales, relevant to the PBH production, can be approximated by. On large scales observed by CMB, the power spectrum is dominated by the inflaton fluctuations and different from Eq (3).
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