Exact Splitting of Amplitudes and One-Loop Integrands: A Classical Origin of Zeros

Abstract

We introduce a recursion based on hidden zeros that reconstructs complete tree level scattering amplitudes and one-loop integrands at generic kinematics. The recursion takes a universal exact-splitting form: both tree amplitudes and one-loop surface integrands are expressed as sums of products of complete tree functions, with the chosen zero conditions manifest in every term. We establish this structure for cubic scalar theory, the nonlinear sigma model, and inverse string Kawai--Lewellen--Tye (KLT) functions. We derive the tree splitting formula from the equations of motion, showing that hidden zeros arise when the product of two currents solves the equations of motion, while corrections away from the zero reconstruct the full amplitude. We further show that inverse KLT is the unique extension of $\mathrm{Tr}(ϕ^3)$ with higher-point non-derivative interactions that preserves hidden zeros.