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| Main Authors: | , , , |
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| Format: | Preprint |
| Published: |
2025
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2509.25129 |
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Table of Contents:
- We study double copy relations for loop integrands in gauge theories and gravity based on their constructions from single cuts, which are in turn obtained from forward limits of lower-loop cases. While such a construction from forward limits has been realized for loop integrands in gauge theories, we demonstrate its extension to gravity by reconstructing one-loop gravity integrands from forward limits of trees. Under mild symmetry assumptions on tree-level kinematic numerators (and their forward limits), our method directly leads to double copy relations for one-loop integrands: these include the field-theoretic Kawai-Lewellen-Tye (KLT) relations, whose kernel is the inverse of a matrix with rank $(n{-}1)!$ formed by those in bi-adjoint $ϕ^3$ theory, and the Bern-Carrasco-Johansson (BCJ) double copy relations with crossing-symmetric kinematic numerators (we provide local and crossing-symmetric Yang-Mills BCJ numerators for $n=3,4,5$ explicitly). By exploiting the "universal expansion" for one-loop integrands in generic gauge theories, we also obtain an analogous expansion for gravity (including supergravity theories).