Excited lepton triplet contribution to electroweak observables at one loop level

TL;DR

This paper calculates one-loop corrections from excited lepton triplets to electroweak precision measurements, showing that non-degenerate excited leptons can significantly impact constraints on new physics models.

Contribution

It provides the first detailed calculation of excited lepton triplet contributions to the $ ho$ parameter at one loop, including effects of mass non-degeneracy.

Findings

Degenerate excited leptons have negligible impact on $ ho$.

Non-degenerate excited leptons can cause large corrections.

Results lead to tighter constraints on excited fermion models.

Abstract

In this paper, we present the one-loop radiative corrections to the electroweak precision observable $\Delta \rho$ coming from the $I_W=1$ multiplet excited leptons. We have calculated the couplings of the exotic lepton triplet to the vector bosons and ordinary leptons using effective Lagrangian approach. These couplings are then used to estimate the excited lepton triplet contribution to the $\Delta \rho$ parameter. The mass degenerate excited lepton contribution to $\Delta \rho $ is small and can be neglected. However, if the excited leptons are non-degenerate, their contribution can be large which can result in more stringent constraints on the excited fermion parameter space compared to the constraints from present experimental searches and perturbative unitarity condition.