Positivity of the Veneziano amplitude in ten dimensions
摘要
The Veneziano amplitude describing the tree-level scattering of four open superstrings is expected to be consistent with unitarity in ten spacetime dimensions. While this follows indirectly from the no-ghost theorem, a direct proof at the level of the amplitude itself only exists for D ≤ 6. In this note, we close this gap by providing a proof for the partial-wave positivity of the Veneziano amplitude in D ≤ 10, derived directly from its representation as the Euler beta function. We also demonstrate that this proof can be modified to show the positivity of a wider family of amplitudes relevant to the S-matrix bootstrap.