Spontaneous Violation Of Lepton Number Research Articles

Majoron decay in matter

It is well known that matter can significantly alter the picture of neutrino oscillation [1] or neutrino decay [2]. Here we show that the presence of dense matter induces also the decay of massless majoron, a Goldstone boson associated with the spontaneous lepton number violation, into a couple of neutrinos with the same (or in some cases also opposite) helicities. We calculate the rates of such matter induced majoron decays in various cases, depending on the neutrino type and the chemical content of the medium, and analyse their properties.

Cosmological consequences of spontaneous lepton number violation in SO(10) grand unification.

Cosmological constraints on grand-unified theories with spontaneous lepton number violation are analyzed. We concentrate on SO(10), the simplest of the models possessing this property. It has been noted previously that the consistency of these models with the observed baryon asymmetry generically implies strict upper bounds on the light neutrino masses. In this paper, we analyze the situation in detail. We find that minimal models of fermion masses face difficulties, but that it is possible for these models to generate an adequate baryon asymmetry via nonequilibrium lepton-number-violating processes when the right-handed neutrino masses are near their maximum possible values. This condition uniquely picks out the minimal gauge symmetry-breaking scheme. A nonminimal model is also analyzed, with somewhat different conclusions due to the nature of the imposed symmetries.

Model-independent Higgs boson mass limits at LEP

We derive model-independent constraints on Higgs mass and couplings from the present LEPI data samples and discuss the prospects for detecting the associated signals for higher masses, accessible at LEPII. This work is motivated by the fact that, in many extensions of the standard model, the Higgs boson can have substantial “invisible” decay modes, for example, into light or massless weakly interacting Goldstone bosons associated to the spontaneous violation of lepton number below the weak scale.

17 keV neutrino in a singlet-triplet majoron model

We investigate the possibility of a cosmologically safe 17 keV neutrino which may have been observed in the decays of tritium, S 35, and C 14 within a singlet-triplet majoron model. Consideration of the leptonic decay of K + and X rays associated with the radiative decay of massive relic neutrinos severely constrains the scale of the spontaneous lepton number violation. It is argued that the mass density of relic 17 keV neutrinos is constrained as Ω v ⩽ 0.05 h −1(0.01/ sin 2 θ) in view of the observed diffuse X ray background.

Is spontaneous breaking of R-parity feasible in minimal low-energy supergravity?

Spontaneous violation of lepton number without breaking Lorentz invariance can, in principle, be incorporated in models with softly broken supersymmetry. We study the situation for minimal low-energy supergravity models coming from a GUT (hence not having hierarchy destabilizing light singlets) and where the SU(2) × U(1) breaking is radiative. It is found that for this type of model, R-parity breaking requires either too heavy a top quark for a realistic superpartner spectrum or too light a superpartner spectrum for a realistic top quark, making the spontaneous violation of lepton number in the third generation incompatible with present experimental data. We do not discard the possibility of having it in a fourth, heavier, generation.

Double beta decay and the neutrino mass

The present state of the problem of the double neutrinoless beta decay, 2β(0ν), and related questions is reviewed. Various mechanisms for ΔL = 2 transitions in models with spontaneous violation of lepton number (L) conservation are discussed. From the standpoint of unified gauge theories, a Majorana neutrino mass would be the most probable reason for processes with ΔL = 2 (if they occur). The 2β(0ν) decay is compared with other phenomena which are sensitive to the neutrino mass. It follows from this comparison that the 2β(0ν) decay is essentially the only process which could be detected at the present level of experimental capabilities and which might tell us about the nature of the neutrino mass, if this mass is some tens of electron volts.

Order of phase transitions in a field theory

The relation between the gauge or global nature of a symmetry being broken and the order of the associated phase transition is clarified. First-order phase transitions in gauge theories are related to the asymptotic freedom of the ${\ensuremath{\Phi}}^{3}$ interaction in six dimensions. Spontaneous violation of lepton number in the standard electroweak theory provides a nontrivial illustration of our results.

Neutrino decay and spontaneous violation of lepton number

The orders of magnitude of decay rates for relatively light neutrinos are studied in the framework of the SU(2)\ifmmode\times\else\texttimes\fi{}U(1) gauge group. The assumption is made that a hierarchy parameter $\ensuremath{\epsilon}(\ensuremath{\approx}(\mathrm{muon}\mathrm{mass})\textdiv{}[\mathrm{some}\mathrm{new}\mathrm{mass}\mathrm{scale}(\mathrm{possibly}\mathrm{much}\mathrm{smaller}\mathrm{than}\mathrm{the}\mathrm{grand}\mathrm{unification}\mathrm{scale})])$ plays a meaningful role in the full theory. For orientation it is first noted that the traditional $\ensuremath{\nu}\ensuremath{\gamma}$ decay channel as well as the $3\ensuremath{\nu}$ decay channel give neutrino lifetimes which for "typical" parameters are substantially longer than the age of the universe. Then we examine in detail some recent proposals which are claimed to result in greatly speeded-up decays into $\ensuremath{\nu}$+Majoron, where the Majoron is a true Goldstone boson associated with spontaneous breakdown of lepton number. In a theory in which the usual Higgs doublet is augmented by a complex singlet (1-2 model) it is noted that the decay width into $\ensuremath{\nu}$+Majoron actually vanishes to order ${\ensuremath{\epsilon}}^{5}$. In a theory where the doublet is augmented by a complex triplet (2-3 model) this decay is shown to vanish exactly, neglecting radiative corrections. A more general Majoron theory (1-2-3 model) is constructed and shown to also yield a vanishing tree-level decay rate for $\ensuremath{\nu}$+Majoron decay to order ${\ensuremath{\epsilon}}^{5}$. Finally, the tree amplitudes in the 1-2 and 1-2-3 models are shown to give decay widths for $\ensuremath{\nu}$+Majoron of order ${\ensuremath{\epsilon}}^{9}$ which correspond to lifetimes much greater than the age of the universe.