Muon to electron conversion in the Littlest Higgs model with T-parity

TL;DR

This paper investigates muon-to-electron conversion in nuclei within the Littlest Higgs model with T-parity, providing detailed one-loop calculations and analyzing the impact of quark mixing on lepton flavor violation.

Contribution

It completes a previous study by including all one-loop contributions and analyzing the most sensitive e conversion channel, offering new insights into constraints on the model.

Findings

Results for Ti nucleus align with previous work assuming degenerate mirror quarks.

Lepton flavor violation constraints impose significant fine-tuning on the model.

The model's compatibility with electroweak precision tests is limited by flavor violation constraints.

Abstract

Little Higgs models provide a natural explanation of the little hierarchy between the electroweak scale and a few TeV scale, where new physics is expected. Under the same inspiring naturalness arguments, this work completes a previous study on lepton flavor-changing processes in the Littlest Higgs model with T-parity exploring the channel that will eventually turn out to be the most sensitive, \mu-e conversion in nuclei. All one-loop contributions are carefully taken into account, results for the most relevant nuclei are provided and a discussion of the influence of the quark mixing is included. The results for the Ti nucleus are in good agreement with earlier work by Blanke et al., where a degenerate mirror quark sector was assumed. The conclusion is that, although this particular model reduces the tension with electroweak precision tests, if the restrictions on the parameter space derived from lepton flavor violation are taken seriously, the degree of fine tuning necessary to meet these constraints also disfavors this model.