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  • Open Access

Unitarity Bounds and Sum Rules in the Standard Model Effective Field Theory

Luigi C. Bresciani1,2,*, Paride Paradisi1,2,†, and Andrea Sainaghi1,2,3,‡

  • *Contact author: luigicarlo.bresciani@phd.unipd.it
  • †Contact author: paride.paradisi@unipd.it
  • ‡Contact author: andrea.sainaghi@phd.unipd.it
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Phys. Rev. Lett. 137, 151801 – Published 9 October, 2026

DOI: https://doi.org/10.1103/v5xg-dmss

Abstract

We present a comprehensive reassessment of perturbative unitarity bounds in the dimension-6 standard model effective field theory, exploiting a new formalism based on spinor-helicity techniques to derive partial-wave unitarity bounds for generic N→M scattering amplitudes. We find that, in several cases, these theoretical constraints are already competitive with, or even stronger than, the corresponding experimental bounds for energy scales above a few TeV. This is especially the case for four-fermion operators under realistic flavor assumptions, where unitarity bounds can be further strengthened by exploiting sum rules. These results provide a valuable and timely contribution toward the ambitious program of new-physics searches with minimal theoretical priors supplemented by restrictive, yet general, first-principles criteria.

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Phys. Rev. Lett. 137, 151801– Published 9 October, 2026
  • Received 23 March 2026
  • Revised 14 July 2026
  • Accepted 11 September 2026
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