  The origin of the graviton from string theory is well understood: it
corresponds to a massless state in closed string spectra, whose low-energy
effective action, as extracted from string scattering amplitudes, is that of
Einstein-Hilbert. In this work, we explore the possibility of such a
string-theoretic emergence of ghost-free bimetric theory, a recently proposed
theory that involves two dynamical metrics, that around particular backgrounds
propagates the graviton and a massive spin-2 field, which has been argued to be
a viable dark matter candidate. By choosing to identify the latter with a
massive spin-2 state of open string spectra, we compute tree-level three-point
string scattering amplitudes that describe interactions of the massive spin-2
with itself and with the graviton. With the mass of the external legs depending
on the string scale, we discover that extracting the corresponding low-energy
effective actions in four spacetime dimensions is a subtle but consistent
process and proceed to appropriately compare them with bimetric theory. Our
findings consist in establishing that string and bimetric theory provide to
lowest order the same set of two-derivative terms describing the interactions
of the massive spin-2 with itself and with the graviton, albeit up to numerical
coefficient discrepancies, a fact that we analyze and interpret. We conclude
with a mention of future investigations.
