  The determination of the inflationary energy scale represents one of the
first step towards the understanding of the early Universe physics. The (very
mild) non-Gaussian signals that arise from any inflation model carry
information about the energy scale of inflation and may leave an imprint in
some cosmological observables, for instance on the clustering of high-redshift,
rare and massive collapsed structures. In particular, the graviton exchange
contribution due to interactions between scalar and tensor fluctuations leaves
a specific signature in the four-point function of curvature perturbations,
thus on clustering properties of collapsed structures. We compute the
contribution of graviton exchange on two- and three-point function of halos,
showing that at large scales $k\sim 10^{-3}\ \mathrm{Mpc}^{-1}$ its magnitude
is comparable or larger to that of other primordial non-Gaussian signals
discussed in the literature. This provides a potential route to probe the
existence of tensor fluctuations which is alternative and highly complementary
to B-mode polarisation measurements of the cosmic microwave background
radiation.
