Imprints of Primordial Non-Gaussianity on Gravitational Wave Spectrum
  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. We show that the statistical properties of the small
scale quantum fluctuations can be probed via the stochastic gravitational wave
background, which is induced as the scalar modes re-enter 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
peaks at a higher frequency and this can result in distinctive observational
signatures. We found that the sensitive next-generation-interferometers, which
will/could reach $\Omega_{GW}h^2 \sim 10^{-15}$ (such as PTA-SKA, LISA, DECIGO,
BBO, CE, ET), can probe $f_{NL} \sim 0.5$ which is even better than the
predictions of the next generation CMB experiments. If the induced GW
background is detected, but not the signatures arising from the non-Gaussian
component, $\zeta = \zeta_G + f_{\rm NL} \, \zeta_G^{2}$, this translates into
bounds on $f_{\rm NL}$ depending on the amplitude and the width of the GW
signal. If the induced GW background is not detected at all, this translates
into bounds on scalar fluctuations. The results are independent from the fact
that whether PBH are DM or completely negligible part of the current energy
density.
