SUSY in the sky --Stochastic gravitational waves from spin 3/2 particles

Quantum system with wavefunction varying non-adiabatically can emit gravitational waves. This usually happens during the preheating where particles are produced from a coherently oscillating scalar. The signals are related to the spin of particles. We use spin 3/2 Rarita-Schwinger action as the sources whose occupation number concentrated within a Fermi-sphere $k_F$. The signals turn out to be much stronger than the one from spin 1/2. Near the peak, the gravitational wave spectrum has a peculiar scaling of $k^5$, which could be the smoking gun signals for spin 3/2 particles. The corresponding frequency is still too high and calls for the ultra-high frequency gravitational wave detectors in the future.