  We present a covariant framework to compute scattering amplitudes and
potentials in a de Sitter background. In this setting, we compute the potential
of a graviton-mediated scattering process involving two very massive scalars at
tree level. Although the obtained scattering potential reproduces the Newtonian
potential at short distances, on Hubble-size length scales it is affected by
the constant curvature: effectively, it yields a repulsive force at sub-Hubble
distances. This can be attributed to the expansion of the de Sitter universe.
Beyond the de Sitter horizon, the potential vanishes identically. Hence, the
scattering amplitude unveils the geometric properties of de Sitter spacetime in
a novel and nontrivial way.
