https://doi.org/10.1140/epjs/s11734-026-02146-9
Review
Unitarity and unitarization
Dept. de Análisis Matemático y Matemática Aplicada and IPARCOS, Universidad Complutense de Madrid, Plaza de las Ciencias 3, 28040, Madrid, Spain
a
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Received:
18
June
2025
Accepted:
19
January
2026
Published online:
29
January
2026
Abstract
This article reviews unitarization methods essential for extending Effective Field Theories (EFTs) beyond their perturbative limits, particularly in hadronic and electroweak (EW) sectors. Perturbative EFTs, like Chiral Perturbation Theory (ChPT), often violate unitarity bounds at higher energies, a breakdown observed in phenomena such as 
scattering resonances. To overcome this, non-perturbative techniques including the Inverse Amplitude Method (IAM), K-matrix formalism, and N/D approach are detailed. The IAM and the N/D methods resume perturbative series while preserving fundamental S-matrix principles: unitarity, analyticity, and causality, dynamically generating resonant behavior. The article emphasizes the unique role of dispersive frameworks, especially the Roy equations, which rigorously incorporate analyticity and crossing symmetry. It highlights their potential for future application in the electroweak sector, offering a powerful tool to constrain the Standard Model and interpret collider data.
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© The Author(s), under exclusive licence to EDP Sciences, Springer-Verlag GmbH Germany, part of Springer Nature 2026
Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
