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  • Open Access

Potential blind directions at TeraZ

Mikael Chala* and Juan Carlos Criado†

Michael Spannowsky‡

  • Departamento de Física Teórica y del Cosmos, Universidad de Granada, Campus de Fuentenueva, E-18071 Granada, Spain

  • *Contact author: mikael.chala@ugr.es
  • †Contact author: jccriadoalamo@ugr.es
  • ‡Contact author: michael.spannowsky@durham.ac.uk
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Phys. Rev. D 113, 035032 – Published 24 February, 2026

DOI: https://doi.org/10.1103/47fb-8vxy

Abstract

The next generation of high-luminosity electron-positron colliders, such as the electron-positron Future Circular Collider and the Circular Electron-Positron Collider operating at the Z pole (TeraZ), is expected to deliver unprecedented precision in electroweak measurements. These precision observables are typically interpreted within the Standard Model effective field theory (SMEFT), offering a powerful tool to constrain new physics. However, the large number of independent SMEFT operators allows for the possibility of blind directions, parameter combinations to which electroweak precision data are largely insensitive. In this work, we demonstrate that such blind directions are not merely an artifact of agnostic effective field theory scans, but arise generically in realistic ultraviolet completions involving multiple heavy fields. We identify several concrete multifield extensions of the Standard Model whose low-energy SMEFT projections align with known blind subspaces, and show that these persist even after accounting for renormalization group evolution and finite one-loop matching effects. Our analysis shows that TeraZ will set a new benchmark in precision for indirect searches, but fully probing the space of possible ultraviolet physics requires going beyond this stage. Later electron-positron Future Circular Collider runs at higher center-of-mass energies, together with the hadron-hadron Future Circular Collider, will provide the necessary complementary probes, enabling a far more complete exploration of the SMEFT parameter space.

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Outline

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Phys. Rev. D 113, 035032– Published 24 February, 2026
  • Received 31 May 2025
  • Accepted 2 February 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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