Abstract
We present a method for building physical projector operators for multi-leg helicity amplitudes. For any helicity configuration of the external particles, we define a physical projector which singles out the corresponding helicity amplitude. For processes with more than four external legs, these physical projectors depend on significantly fewer tensor structures and exhibit a remarkable simplicity compared with projector operators defined with traditional approaches. As an example, we present analytic formulas for a complete set of projectors for five-gluon scattering. These have been validated by reproducing known results for five-gluon amplitudes up to one-loop.
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Peraro, T., Tancredi, L. Physical projectors for multi-leg helicity amplitudes. J. High Energ. Phys. 2019, 114 (2019). https://doi.org/10.1007/JHEP07(2019)114
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DOI: https://doi.org/10.1007/JHEP07(2019)114