$2$-Split of Form Factors via BCFW Recursion Relation

Abstract

Recently, \cite{Cao:2025hio} demonstrated the $2$-split for form factor under specific kinematic constraints. This factorization is analogous to that observed in scattering amplitudes. A key consequence of this structure is the presence of hidden zeros, where the form factors vanish on specific kinematic loci. We first establish these zeros and a new zero for the form factors of the composite operators ${\cal O} =\frac{1}{2}\Tr((\partial \phi)^2) + \Tr(\phi^3)$ and ${\cal O} = \Tr(F^2)$, and then employ an inductive proof based on the BCFW recursion relation to prove the $2$-split factorization for any number of external particles.