On interference and non-interference in the SMEFT

  • Andreas Helset
  • Michael Trott
Open Access
Regular Article - Theoretical Physics


We discuss interference in the limit \( {\widehat{m}}_W^2/s\to 0 \) in the Standard Model Effective Field Theory (SMEFT). Dimension six operators that contribute to \( \overline{\psi}\psi \to \overline{\psi}{\prime}_1\psi {\prime}_2\overline{\psi}{\prime}_3\psi {\prime}_4 \) scattering events can experience a suppression of interference effects with the Standard Model in this limit. This occurs for subsets of phase space in some helicity configurations. We show that approximating these scattering events by 2 → 2 on-shell scattering results for intermediate unstable gauge bosons, and using the narrow width approximation, can miss interference terms present in the full phase space. Such interference terms can be uncovered using off-shell calculations as we explicitly show and calculate. We also study the commutation relation between the SMEFT expansion and the narrow width approximation, and discuss some phenomenological implications of these results.


Beyond Standard Model Effective Field Theories Scattering Amplitudes 


Open Access

This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.


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Copyright information

© The Author(s) 2018

Authors and Affiliations

  1. 1.Niels Bohr International Academy and Discovery Centre, Niels Bohr InstituteUniversity of CopenhagenCopenhagenDenmark

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