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Flavor Constraints from Unitarity and Analyticity

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arxiv 2004.02885 v3 pith:VVEVYAYO submitted 2020-04-06 hep-ph hep-th

classification hep-phhep-th
keywords operatorsanalyticityconstraintsflavormodelstandardunitarityalready
verification ladder T0 review T1 audit T2 compute T3 formal

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abstract

We use unitarity and analyticity of scattering amplitudes to constrain fermionic operators in the standard model effective field theory. For four-fermion operators at mass dimension 8, we scatter flavor superpositions in fixed standard model representations and find the Wilson coefficients to be constrained so that their contraction with any pair of pure density matrices is positive. These constraints imply that flavor-violating couplings are upper-bounded by their flavor-conserving cousins. For instance, LEP data already appears to preclude certain operators in upcoming $\mu \to 3e$ measurements.

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Forward citations

Cited by 11 Pith papers

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

  1. Multipositivity Bounds for Scattering Amplitudes

    hep-th 2025-05 conditional novelty 8.0 of 10

    Scattering residues at any multiplicity form positive semidefinite moment matrices, yielding an infinite web of multipositivity bounds that the open string exactly saturates.

  2. Positivity in the Renormalization of Effective Field Theory

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    A general theorem fixes the sign of one-loop renormalization of even-dimension EFT couplings induced by equal-even-dimension operator pairs, with applications to SMEFT dimension-eight running and new non-renormalizati...

  3. Partial Waves for Multipositivity

    hep-th 2026-08 conditional novelty 7.0 of 10

    The paper constructs kinematic charts and partial-wave expansions for four-, five-, and six-point massless planar amplitudes tailored to multipositivity bounds.

  4. Unitary Dual-Resonance S-matrices

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    Smearing Veneziano blocks over continuous Regge slopes yields local, analytic, crossing-symmetric S-matrices with full partial-wave unitarity and controllable second-sheet resonances.

  5. Geometry of effective field theory positivity cones

    math-ph 2025-08 accept novelty 7.0 of 10

    For three particle flavors, the positivity cone C_W has exactly three families of extremal rays, one of which yields genuinely new inelastic constraints not implied by elastic bounds.

  6. Strings from Almost Nothing

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  7. Towards the HEFT-hedron: the complete set of positivity constraints at NLO

    hep-ph 2024-12 conditional novelty 7.0 of 10

    Complete positivity constraints from causality and unitarity are derived for the 15 NLO HEFT operators contributing to longitudinal gauge-Higgs scattering, shrinking the allowed space to about 5 percent.

  8. Matrix moment approach to positivity bounds and UV reconstruction from IR

    hep-th 2024-11 conditional novelty 7.0 of 10

    Positivity bounds for multi-field EFTs are formulated as matrix moment problems, yielding optimal bounds and a method to reverse engineer the UV mass, spin, and coupling spectrum from low-energy coefficients.

  9. S-matrix bootstrap bounds on self-interacting dark matter

    hep-ph 2026-07 conditional novelty 6.0 of 10

    Weakly coupled scalar self-interacting dark matter cannot be heavier than ~0.3 GeV (generic) or ~MeV (derivative-coupled pNGB), much tighter than the 12 GeV unitarity bound.

  10. Positivity and partial wave unitarity bounds on ALP theories via amplitude methods

    hep-ph 2025-10 conditional novelty 6.0 of 10

    Complete partial-wave unitarity and positivity bounds are derived for ALP effective interactions up to dimension 8, with new SMEFT positivity constraints as a byproduct.

  11. Targets for Flavor-Violating Top Decay

    hep-ph 2025-04 accept novelty 6.0 of 10

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