Prospects for new physics in $\tau \to l \mu \mu$ at current and future colliders

TL;DR

This paper assesses the potential of current and future colliders to detect lepton flavor violation in tau decays, providing new constraints on physics beyond the Standard Model such as the Type-II Seesaw, Left-Right Symmetric, and MSSM models.

Contribution

It evaluates the discovery prospects for tau lepton flavor violating decays at colliders and derives expected constraints on new physics parameters.

Findings

LHC Run 13 TeV can outperform existing limits for certain tau decays.

Future circular e+e- colliders could reach branching fraction sensitivities of 10^{-12}.

Constraints on new physics models can be significantly improved with collider data.

Abstract

The discovery of lepton flavour violating interactions will be striking evidence for physics beyond the Standard Model. Focusing on the three decays $\tau^\mp \to \mu^\pm \mu^\mp \mu^\mp$, $\tau^\mp \to e^\pm \mu^\mp \mu^\mp$ and $\tau^\mp \to e^\mp \mu^\mp \mu^\pm$, we evaluate the discovery potential of current and future high-energy colliders to probe lepton flavour violation in the $\tau$ sector. Based on this potential we determine the expected constraints on parameters of new physics in the context of the Type-II Seesaw Model, the Left-Right Symmetric Model, and the Minimal Supersymmetric Standard Model. The existing and ongoing 13 TeV run of the Large Hadron Collider has the potential to produce constraints that outperform the existing $e^+ e^-$ collider limits for the $\tau^\mp \to \mu^\pm \mu^\mp \mu^\mp$ decay and achieve a branching fraction limit of $\lesssim 10^{-8}$. With a future circular $e^+ e^-$ collider, constraints on the $\tau \to l \mu \mu$ branching fractions could reach as low as a few times $10^{-12}$.