Where Is String Theory in the Space of Scattering Amplitudes?

Abstract

We use the S-matrix bootstrap to carve out the space of unitary, crossing symmetric and supersymmetric graviton scattering amplitudes in ten dimensions. We focus on the leading Wilson coefficient α controlling the leading correction to maximal supergravity. The negative region α<0 is excluded by a simple dual argument based on linearized unitarity (the desert). A whole semi-infinite region αâ 0.14 is allowed by the primal bootstrap (the garden). A finite intermediate region is excluded by nonperturbative unitarity (the swamp). Remarkably, string theory seems to cover all (or at least almost all) the garden from very large positive α-At weak coupling-To the swamp boundary-At strong coupling.