Phenomenology of neutral heavy leptons

Abstract

Naturally small neutrino masses can arise in some grand unified models. The mechanism of neutrino mass generation in these models typically requires the existence of neutral heavy leptons. We study the low-energy phenomenology of these new fermions. Concentrating on loop corrections due to neutral heavy leptons, we examine how the flavour-conserving leptonic decays of the Z boson, universality breaking in these decays, and the W boson mass depend on the mass and mixings of the neutral heavy leptons. Working within the framework of a superstring-inspired SU(2) L × U(1) Y model, we show that these flavour-conserving processes have some virtues over the traditionally considered flavour-violating decays.i

Left–right symmetry and heavy particle quantum effects

“…This can be easily seen, with some dimensional analysis. Fortunately, it has been proved in the case of the SM with additional right handed singlets [3], that these terms cancel with similar contributions from the external wave functions. Since the proof can be made by explicit calculation 14 , and in this respect nothing changes if we go over to the LR model, here also these terms cancel.…”

“…Additional problems appear in models where heavy neutrinos are introduced. This has been examined in the frame of the SM with additional isosinglet neutrino fields (which build up Dirac neutrinos) [3]. Then, the interplay between heavy neutrinos and light standard particles on the one hand, and nondecoupling effects [4] on the other, is important .…”

“…We begin with four neutral scalars H 0 a , a = 0, 1, 2, 3, and two neutral pseudoscalars A 0 1,2 3 :…”

Pseudoscalar boson and standard model-like Higgs boson productions at the LHC in the simplest little Higgs model

“…where g f L and g f R are from the coupling Z ′f γ µ (g f L P L + g f R P R )f , which can be found in [6,33].…”

“…Since the coupling is suppressed by v 2 f 2 and without enhancement of t β , the decay mode Z ′ → W W is neglected here. The decay modes Z ′ → Y 0 Y 0 and Z ′ → X + X − are forbidden kinematically [6,11,33].…”