# Vectorlike lepton imprints at lepton $g-2$ measurements and $e^+e^-$ colliders

## TL;DR

This paper explores how vectorlike leptons influence lepton g-2 measurements and collider signals, identifying viable parameter spaces and prospects for future tests at FCC-ee with high precision.

## Contribution

It introduces an extension of the Standard Model with vectorlike leptons and scalars, analyzing their effects on lepton g-2 and collider processes, and assesses future experimental sensitivities.

## Key findings

- Model explains current g-2 anomalies within viable parameter space.
- FCC-ee can significantly constrain or exclude parts of the model.
- High-precision measurements at FCC-ee will test the model's predictions.

## Abstract

A fermion can be chiral or vectorlike with respect to a given symmetry, depending on its coupling to the corresponding gauge boson. Vectorlike fermions have a distinct property that their left-handed and right-handed components behave in the same way under the gauge symmetry. In this paper, we investigate an extension of the standard model with an $SU(2)$ doublet of vectorlike leptons and two complex scalars. The new physics effects on the lepton anomalous magnetic moment, as well as the electron and muon pair production processes at $e^+e^-$ colliders are analyzed. Taking into account the updated measurement results of the electron and muon $g-2$, the LEP and the LHC data, the viable parameter space of the model is identified. We also examine the prospect of testing the model using $\mu^+\mu^-$ signals from electron-position annihilation at the Future Circular Collider (FCC-ee). The analysis shows that the FCC-ee will be able to exclude a significant part of the parameter space, pinpointing exiguous viable regions to be tested in the future due to its high precision.