Axion Curvaton Model for the Gravitational Waves Observed by Pulsar Timing Arrays

The stochastic gravitational wave background (SGWB) recently detected by the PTA collaborations could be the gravitational waves (GWs) induced by curvature perturbations. However, primordial black holes (PBHs) might be overproduced if the SGWB is explained by the GWs induced by the curvature perturbations that follow the Gaussian distribution. This motivates models associated with the non-Gaussianity of the curvature perturbations that suppress the PBH production rate. In this work, we show that the axion curvaton model can produce the curvature perturbations that induce GWs for the detected SGWB while preventing the PBH overproduction with the non-Gaussianity.