The proposed recursion relation determines tree-level NLSM amplitudes, revealing hidden zeros and Adler zero features.
In this note, we propose a novel BCFW-like recursion relation for tree-level non-linear sigma model (NLSM) amplitudes, which circumvents the computation of boundary terms by exploiting the recently discovered hidden zeros. Using this recursion, we reproduce three remarkable features of tree-level NLSM amplitudes: (i) the Adler zero, (ii) the $δ$-shift construction, which generates NLSM amplitudes from Tr(ϕ³) amplitudes, and (iii) the universal expansion of NLSM amplitudes into bi-adjoint scalar amplitudes. Our results demonstrate that the hidden zero, combined with standard factorization on physical poles, uniquely determines all tree-level NLSM amplitudes.
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Li et al. (2025) studied this question.
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