Current and future constraints on heavy New Physics from $\tau$ weak dipole moments

Nejc Košnik; Zachary Polonsky; Aleks Smolkovič

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arXiv · 2606.07232

Current and future constraints on heavy New Physics from $\tau$ weak dipole moments

Nejc Košnik·Zachary Polonsky·Aleks Smolkovič

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Abstract

We study the weak magnetic and electric dipole moments of the $\tau$ lepton as precision tests of the Standard Model (SM) and probes of heavy New Physics (NP). We present an updated SM prediction for the $\tau$ weak magnetic dipole moment at one loop, including a careful assessment of theoretical uncertainties from electroweak scheme dependence. Working within the SM Effective Field Theory, we derive comprehensive current constraints on the $\tau$ dipole operators from a combination of observables: the $\tau$ weak and electromagnetic dipole moments, high-mass Drell-Yan tails at the LHC, $Z$ partial decay widths, and the electron electric dipole moment. Finally, we assess the prospects of measuring the SM value of the $\tau$ weak magnetic moment at the FCC-$ee$ Tera-$Z$ run, and project the sensitivities of the leading observables to heavy NP at FCC-$ee$ and HL-LHC, paying particular attention to systematic uncertainties. We find that the $\tau$ weak dipole moments are already among the leading probes of the $\tau$ dipole operators, and will become increasingly dominant at future colliders.

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Nejc Košnik, Zachary Polonsky, Aleks Smolkovič. 2026-06-05. Current and future constraints on heavy New Physics from $\tau$ weak dipole moments. https://arxiv.org/abs/2606.07232

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