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Loops and trees

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arxiv 1007.3224 v1 pith:GY7XSK7Z submitted 2010-07-19 hep-ph hep-th

classification hep-phhep-th
keywords forwardlimitlooploopsphysicaltreeamplitudeamplitudes
verification ladder T0 review T1 audit T2 compute T3 formal
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We investigate relations between loop and tree amplitudes in quantum field theory that involve putting on-shell some loop propagators. This generalizes the so-called Feynman tree theorem which is satisfied at 1-loop. Exploiting retarded boundary conditions, we give a generalization to L-loop expressing the loops as integrals over the on-shell phase space of exactly L particles. We argue that the corresponding integrand for L>2 does not involve the forward limit of any physical tree amplitude, except in planar gauge theories. In that case we explicitly construct the relevant physical amplitude. Beyond the planar limit, abandoning direct integral representations, we propose that loops continue to be determined implicitly by the forward limit of physical connected trees, and we formulate a precise conjecture along this line. Finally, we set up technology to compute forward amplitudes in supersymmetric theories, in which specific simplifications occur.

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Forward citations

Cited by 6 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Perturbative construction of amplitudes from on-shell trees with vacuum pairs: the all-plus four-gluon amplitude through order $\boldsymbol{g}^{\boldsymbol{6}}$

    hep-th 2026-06 unverdicted novelty 7.0 of 10

    An on-shell construction using BCFW trees plus vacuum-pair phase-space integrals with inclusion-exclusion signs reproduces the known one- and two-loop all-plus four-gluon amplitudes.

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    Worldline gravitational observables can be bootstrapped from locality, unitarity, gauge invariance, and a soft theorem once worldline energies are complexified, reproducing the known O(G^5/2) waveform and O(G^3) on-sh...

  3. Systematic approach to $\ell$-loop planar integrands from the classical equation of motion

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    A recursion formula for ℓ-loop planar integrands in colored QFTs is derived from the classical equation of motion via comb components and loop kernels.

  4. On one-loop amplitudes in gauge theories

    hep-th 2024-12 conditional novelty 6.0 of 10

    A universal expansion expresses one-loop n-gluon amplitudes in general gauge theories as scalar-loop integrands dressed by matter-dependent gauge-invariant traces.

  5. Weak-field waveforms for generic relativistic orbits

    hep-th 2026-06 unverdicted novelty 5.0 of 10

    Outlines a Schwinger-Keldysh path-integral framework that derives worldline equations of motion and computes weak-field gravitational waveforms independently for unspecified relativistic orbits.

  6. QCD-Gravity double copy in Regge asymptotics: from $2\rightarrow n$ amplitudes to radiation in shockwave collisions

    hep-th 2025-07 accept novelty 3.0 of 10

    A lecture-note synthesis showing that the same Lipatov vertices and reggeized propagators govern multi-particle production in QCD and gravity, with double-copy, Weinberg soft, and shockwave limits all connected in one...

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