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Four-dimensional Minkowskian scattering amplitudes can also be presented in a basis of a different group (S00exL(2,C)), which acts as the conformal group on the celestial two-sphere at null infinity. This type of representation is useful for understanding the flat-space holography. The authors propose a procedure for taking the (conformally) soft limit of tree-level scattering amplitudes in this basis.
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Pate et al. (2019) studied this question.
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