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Impact of new physics on momentum-dependent particle widths and propagators

Christoph Englert1,*, Wrishik Naskar1,†, and Michael Spannowsky2,‡

  • 1School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, United Kingdom
  • 2Institute for Particle Physics Phenomenology, Department of Physics, Durham University, Durham DH1 3LE, United Kingdom

  • *Contact author: christoph.englert@glasgow.ac.uk
  • †Contact author: w.naskar.1@research.gla.ac.uk
  • ‡Contact author: michael.spannowsky@durham.ac.uk
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Phys. Rev. D 111, 055017 – Published 17 March, 2025

DOI: https://doi.org/10.1103/PhysRevD.111.055017

Abstract

We investigate the impact of momentum-dependent particle widths and propagators on gauge and Higgs bosons and the top quark within the Standard Model (SM) and its effective field theory (SMEFT) extensions near thresholds. By incorporating self-energy corrections via Dyson resummation, we quantify deviations from the fixed-width approximation and assess their implications for collider observables. While effects on the Higgs boson are negligible and the W boson shows percent-level deviations in reconstructed transverse mass distributions, the top quark exhibits significant sensitivity near its mass threshold. Future lepton colliders, e.g., electron-positron machines or muon colliders, can offer sensitivity to these effects, enabling constraints on SMEFT Wilson coefficients. We perform a representative case study for the precision frontier available with a staged future muon collider. Our results highlight that momentum dependencies can provide additional sensitivity at precision-era experiments, enhancing the potential for discovering new physics there.

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Phys. Rev. D 111, 055017– Published 17 March, 2025
  • Received 24 January 2025
  • Accepted 19 February 2025
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