Probing $\tau$ lepton dipole moments at future Lepton Colliders

TL;DR

Future lepton colliders like FCC and muon colliders could significantly improve constraints on the $ au$ lepton's dipole moments, which are currently weakly constrained, through various production and decay channels.

Contribution

This paper evaluates the potential of upcoming lepton colliders to probe $ au$ dipole moments, demonstrating their ability to vastly improve current bounds.

Findings

Colliders can extend bounds on $ au$ dipole moments by several orders of magnitude.

Multiple channels provide complementary sensitivity to $ au$ dipole moments.

Future colliders are highly effective in probing $ au$ dipole moments compared to current constraints.

Abstract

The electric and magnetic dipole moments of the electron and of the muon provide stringent tests of the Standard Model and sensitive probes of new physics. By contrast, the corresponding dipole moments of the $\tau$ lepton remain weakly constrained. This study explores the potential of future lepton colliders, focusing on the $e^+e^-$ Future Circular Collider and a multi-TeV muon collider, to probe $\tau$ dipole moments. We consider multiple channels, including $\ell^+\ell^- \to \tau^+\tau^-$ ($\ell=e,\mu$), associated Higgs production $\mu^+\mu^- \to \tau^+\tau^- H$, radiative Higgs decays $H \to \tau^+\tau^-\gamma$, and vector-boson scattering $\ell^+\ell^- \to \ell^+\ell^-\tau^+\tau^-$ and $\mu^+\mu^- \to \bar\nu\nu\tau^+\tau^-$. Our results show that these facilities are highly complementary and can extend existing bounds by several orders of magnitude.