Although cosmic microwave background and large scale structure probe the largest scales of our Universe with ever-increasing precision, our knowledge about the smaller scales is still very limited other than the bounds on primordial black holes (PBHs). We show that the statistical properties of the small scale quantum fluctuations can be probed via the stochastic gravitational wave (GW) background, which is induced as the scalar modes reenter the horizon. We found that even if scalar curvature fluctuations have a subdominant non-Gaussian component, these non-Gaussian perturbations can source a dominant portion of the induced GWs. Moreover, the GWs sourced by non-Gaussian scalar fluctuations peak at a higher frequency and this can result in distinctive observational signatures. If the induced GW background is detected, but not the signatures arising from the non-Gaussian component, ζ=ζG+fNLζG2, this translates into bounds on fNL depending on the amplitude and the width of the GW signal. The results are independent of the fact that whether PBHs are dark matter or a completely negligible part of the current energy density.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)