Effects of new leptons in electroweak precision data

Abstract

We obtain limits on generic vector-like leptons at the TeV scale from electroweak precision tests. These limits are complementary to the ones obtained from lepton flavour violating processes. In general, the quality of the global electroweak fit is comparable to the one for the Standard Model. In the case of an extra neutrino singlet mixing with the muon or electron, the global fit allows for a relatively large Higgs mass (M H 260 GeV at 90 % C.L.), thus relaxing the tension between the direct LEP limit and the Standard Model fit. *

Sterile neutrinos in leptonic and semileptonic decays

“…of theoretical analyses [55,56] with the recent measurements from the NA62 collaboration [57,58] and with the existing measurements on pion leptonic decays [59] 23) suggests that observation agrees at the 1σ level with the SM predictions for…”

“…In the presence of singlet neutrinos, electroweak precision constraints were first addressed in [23] and recently studied in [24,25]. In [23], an effective approach was used, and thus these constraints will only be considered in cases with multi-TeV singlet states. Our numerical results, which will be presented in section 4, are in agreement with the results of [24,25].…”

Dark matter and lepton flavour violation in a hybrid neutrino mass model

“…In addition to LFV and the DM abundance, the other important constraint on our model comes from the EW precision data, which limits the mixing between the active and sterile neutrinos and therefore the Yukawa couplings y αi . With the absence of standard Yukawa couplings of heavy neutrinos with the electron doublet, the relevant limits on the light-heavy mixing are [46] |V µi | 2 < 3 × 10 −3 , 1) with i = 2, 3. These limits can be translated to the Yukawa couplings using V αi = y αi v/m N i .…”

Minimal muon anomalous magnetic moment

“…Actually these are the only fermion fields which mix with leptons at tree level respecting the SM gauge invariance; their effect on EW observable have been studied in refs. [17,18].…”