Extracting bigravity from string theory

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