Primordial black holes and scalar induced gravitational waves from sound speed resonance in derivatively coupling inflation model

Abstract: We study the amplification of primordial curvature perturbations through a sound speed resonance mechanism within an inflationary model featuring a non-minimal derivative coupling. In this scenario, the coupling function is composed of a constant term and a periodic term. Our analysis demonstrates that the periodic behavior of the squared sound speed transforms the curvature perturbation equation into a Mathieu equation on sub-horizon scales. This resonance effect leads to a substantial enhancement of curvature perturbations, which, upon re-entering the Hubble horizon during the radiation-dominated era, can trigger the formation of primordial black holes, potentially contributing to the dark matter density. Additionally, the amplified perturbations generate scalar-induced gravitational waves with amplitudes that may lie within the detectable range of future gravitational wave observatories, providing a testable observational signature of the model.