Gravitational Wave Probe of Gravitational Dark Matter from Preheating

We forecast high-frequency gravitational wave (GW) from preheating hosting gravitational dark matter (GDM) as the indirect probe of such GDM. We use proper lattice simulations to handle resonance, and to solve GW equation of motion with the resonance induced scalar field excitations as source term. Our numerical results show that Higgs scalar excitations in Higgs preheating model give rise to magnitudes of GW energy density spectra of order $10^{-10}$ at frequencies $10-10^{3}$ MHz depending on the GDM mass, whereas inflaton fluctuation excitations in inflaton self-resonant preheating model yield magnitudes of GW energy density spectrum up to $10^{-9}~(10^{-11})$ at frequencies near $30~(2)$ MHz for the index $n=4~(6)$ with respect to the GDM mass of $1.04~(2.66)\times 10^{14}$ GeV.