Uniqueness from locality and BCFW shifts

Abstract

Abstract We introduce a BCFW shift that can be used to recursively build the full YangMills tree-level amplitude as a function of polarization vectors. Furthermore, in line with the recent results of [1], we conjecture that the Yang-Mills tree-level scattering amplitude is uniquely fixed by locality and demanding the usual asymptotic behavior under a sufficient number of shifts. Unitarity therefore emerges from locality and constructability. We prove this statement at the leading order in the soft expansion.