Precise limits from lepton flavour violating processes on the littlest Higgs model with T-parity

Abstract

We recalculate the leading one-loop contributions to µ → eγ and µ → eeē in the Littlest Higgs model with T-parity, recovering previous results for the former. When all the Goldstone interactions are taken into account, the latter is also ultraviolet finite. The present experimental limits on these processes require a somewhat heavy effective scale ∼ 2.5 TeV, or the flavour alignment of the Yukawa couplings of light and heavy leptons at the ∼ 10% level, or the splitting of heavy lepton masses to a similar precision. Present limits on τ decays set no bounds on the corresponding parameters involving the τ lepton.

Lepton flavor violation in the Simplest Little Higgs model

“…Only normalized values below the unity are experimentally allowed. The general behavior of the SLH model is very similar to that of the LHT model studied previously in [18,19]. Tables 11 and 12 contain generic constraints on the scale f , δ and sin 2θ for standard values for the rest of the parameters in each case.…”

“…These amplitudes are ultraviolet finite, as they are in the case of the LHT model [18,19,21,22]. On the other hand, the heavy neutrino Yukawa exhibits a nondecoupling behavior (figure 5): both Z and Z ′ penguin contributions to the amplitudes grow with m 2 N /M 2 X , a result that is well known and was discussed in [18,19]. To simplify the phenomenological analysis, we have assumed, as in previous studies, that only two lepton families mix.…”

“…We follow closely the analysis in [18,19] and restrict ourselves to the case of two lepton families to illustrate the physical behavior of the amplitudes. This leaves us with four basic parameters:…”

“…Hence, the corresponding limits can be satisfied sending f to a high enough value or aligning both sectors with a high enough precision. For instance, in the Littlest Higgs model with T-parity (LHT) present bounds on lepton flavor violating (LFV) processes require f > ∼ 10 TeV or a misalignment of at most 1% between the SM and the heavy fermion mass matrices [16][17][18][19]. These limits are not stronger because T-parity forbids tree-level flavor changing Z couplings.…”

LHC diphoton Higgs signal predicted by little Higgs models

“…Here, we assume the new flavor mixing matrices in lepton and quark sectors are diagonal [5,25], so that f and t β are free from the experimental constraints of the lepton and quark flavor violating processes. In addition, the contributions to the electroweak precision data can be suppressed by the large t β [4,26]. For the perturbation to be valid, t β cannot be too large for a fixed f .…”