Exploring the NANOGrav Signal and Planet-mass Primordial Black Holes through Higgs Inflation
The data recently released by the North American Nanohertz Observatory for Gravitational Waves provides compelling evidence supporting the existence of a stochastic signal that aligns with a gravitational-wave background. We show this signal can be the scalar-induced gravitational waves from the Higgs inflation model with the parametric amplification mechanism. Such a gravitational-wave background naturally predicts the substantial existence of planet-mass primordial black holes, which can be planet 9 in our solar system and the lensing objects for the ultrashort-timescale microlensing events observed by the Optical Gravitational Lensing Experiment. The future observations of stochastic gravitational wave background by pulsar timing arrays and planet-mass primordial black holes provide such a possibility to give further confirmations on Higgs inflation, which unifies two fundamental aspects of theoretical physics, particle physics and cosmology.