Probe of spatial geometry from scalar induced gravitational waves

We investigate a novel probe of spatial geometry of the Universe through the observation of gravitational waves (GWs) induced by first order curvature perturbations. The existence of spatial curvature leaves imprints on the gravitational wave spectrum and formation of primordial black holes. Given the peaked scalar spectrum, the induced spectrum deviates from the flat space power spectrum and the deviation is dependent on the spatial curvature K and reheating temperature $T_{rh}$. For prolonged reheating and negative spatial curvature the spectrum is amplified enough and exhibits an additional peak solely due to K indicating a possible detection by future gravitational wave experiments including LISA and DECIGO. We also observe that the presence of negative spatial curvature improves the constraints on PBH formation, increasing the mass of black holes which are viable dark matter candidates.
Comment: 21 pages,4 Figures, 10 pages of supplementary material with 5 Appendices