Detecting Collective Excitations in Self-Gravitating Bose-Einstein Condensates via Faraday Waves

Abstract: We propose Faraday waves as a probe for collective excitations in self-gravitating Bose-Einstein condensates (SGBECs), driven by periodic modulation of the $s$-wave scattering length. Linear stability analysis of the driven Gross-Pitaevskii-Newton equations reveals that parametric instability follows a Mathieu-like equation, with Faraday waves emerging resonantly when half the driving frequency matches the collective excitation frequency of the SGBEC. This framework yields a stability phase diagram demonstrating the coexistence and interplay between the intrinsic Jeans instability of self-gravitating systems and the unstable tongues of parametric resonance. The phase diagram shows that reducing the driving frequency fragments and narrows parametric resonance structures while expanding the Jeans-dominated regime. We further identify a thermal-gravity competition in the Faraday wavevector, manifested as a sharp transition when thermal energy balances mean-field interaction at low driving frequencies. We numerically simulate Faraday wave formation and dynamics within the SGBEC, including the effects of dissipation; simulations reveal that Faraday wave patterns exhibit high sensitivity to Jeans frequency, transitioning from parametric resonance to Jeans collapse as gravitational strength increases.