Emergence of Unitarity and Locality from Hidden Zeros at One-Loop

Abstract: Recent investigations into the geometric structure of scattering amplitudes have revealed the surprising existence of hidden zeros'': secret kinematic loci where tree-level amplitudes in Tr$(\phi^3)$ theory, the Non-Linear Sigma Model (NLSM), and Yang-Mills theory vanish. In this letter, we propose the extension of hidden zeros to one-loop-order in Tr$(\phi^3)$ theory and the NLSM using thesurface integrand'' technology introduced by Arkani-Hamed et al. We demonstrate their power by proving that, under the assumption of locality, one-loop integrands in Tr$(\phi^3)$ are unitary if and only if they satisfy the loop hidden zeros. We also present strong evidence that the hidden zeros themselves contain the constraints from locality, leading us to conjecture that the one-loop Tr$(\phi^3)$ integrand can be fixed by hidden zeros from a generically non-local, non-unitary ansatz. Near the one-loop zeros, we uncover a simple factorization behavior and conjecture that NLSM integrands are fixed by this property, also assuming neither locality nor unitarity. This work represents the first extension of such uniqueness results to loop integrands, demonstrating that locality and unitarity emerge from other principles even beyond leading order in perturbation theory.