Enumerating higher-dimensional operators with on-shell amplitudes

Understand

We establish a simple formula for the minimal dimension of operators leading to any helicity amplitude.

• It eases the systematic enumeration of independent operators from the construction of massless non-factorizable on-shell amplitudes.
• Little-group constraints can then be solved algorithmically for each helicity configuration to extract a complete set of spinor structures with lowest dimension.
• Occasionally, further reduction using momentum conservation, on-shell conditions and Schouten identities is required.