233 research outputs found
Decay of the Z Boson into Scalar Particles
In extensions of the standard model, light scalar particles are often
possible because of symmetry considerations. We study the decay of the Z boson
into such particles. In particular, we consider for illustration the scalar
sector of a recently proposed model of the 17-keV neutrino which satisfies all
laboratory, astrophysical, and cosmological constraints.Comment: 11 pages (2 figures, not included) (Revised, Oct 1992). Some
equations have been corrected and 1 figure has been eliminate
Light-Heavy Symmetry: Geometric Mass Hierarchy for Three Families
The Universal Seesaw pattern coupled with a LightHeavy
symmetry principle leads to the Diophantine equation , where and distinct. Its unique non-trivial
solution gives rise to the geometric mass hierarchy ,
, for fermion families. This is realized in
a model where the hybrid (yet UpDown symmetric) quark mass
relations play a
crucial role in expressing the CKM mixings in terms of simple mass ratios,
notably .Comment: 12 pages, no figures, Revtex fil
Radiative Seesaw Mechanism at Weak Scale
We investigate an alternative seesaw mechanism for neutrino mass generation.
Neutrino mass is generated at loop level but the basic concept of usual seesaw
mechanism is kept. One simple model is constructed to show how this mechanism
is realized. The applications of this seesaw mechanism at weak scale to
cosmology and neutrino physics are discussed.Comment: 12 Pages, latex, no figure
A New Class of Majoron-Emitting Double-Beta Decays
Motivated by the excess events that have recently been found near the
endpoints of the double beta decay spectra of several elements, we re-examine
models in which double beta decay can proceed through the neutrinoless emission
of massless Nambu-Goldstone bosons (majorons). Noting that models proposed to
date for this process must fine-tune either a scalar mass or a VEV to be less
than 10 keV, we introduce a new kind of majoron which avoids this difficulty by
carrying lepton number . We analyze in detail the requirements that
models of both the conventional and our new type must satisfy if they are to
account for the observed excess events. We find: (1) the electron sum-energy
spectrum can be used to distinguish the two classes of models from one another;
(2) the decay rate for the new models depends on different nuclear matrix
elements than for ordinary majorons; and (3) all models require a (pseudo)
Dirac neutrino, having a mass of a several hundred MeV, which mixes with
.Comment: 43 pages, 10 figures (included), [figure captions are now included
Topologically Stable Electroweak Flux Tube
We show that for a large range of parameters in a
electroweak theory with two Higgs doublets there may exist classically stable
flux tubes of Z boson magnetic field. In a limit of an extra global symmetry, these flux-tubes become topologically stable. These results are
automatically valid even if is gauged.Comment: 10 pages, LATE
Tritium Beta Decay, Neutrino Mass Matrices and Interactions Beyond the Standard Model
The interference of charge-changing interactions, weaker than the V-A
Standard Model (SM) interaction and having a different Lorentz structure, with
that SM interaction, can, in principle, produce effects near the end point of
the Tritium beta decay spectrum which are of a different character from those
produced by the purely kinematic effect of neutrino mass expected in the
simplest extension of the SM. We show that the existence of more than one mass
eigenstate can lead to interference effects at the end point that are stronger
than those occurring over the entire spectrum. We discuss these effects both
for the special case of Dirac neutrinos and the more general case of Majorana
neutrinos and show that, for the present precision of the experiments, one
formula should suffice to express the interference effects in all cases.
Implications for "sterile" neutrinos are noted.Comment: 32 pages, LaTeX, 6 figures, PostScript; full discussion and changes
in notation from Phys. Lett. B440 (1998) 89, nucl-th/9807057; submitted to
Phys. Rev.
Neutrinos, Axions and Conformal Symmetry
We demonstrate that radiative breaking of conformal symmetry (and
simultaneously electroweak symmetry) in the Standard Model with right-chiral
neutrinos and a minimally enlarged scalar sector induces spontaneous breaking
of lepton number symmetry, which naturally gives rise to an axion-like particle
with some unusual features. The couplings of this `axion' to Standard Model
particles, in particular photons and gluons, are entirely determined (and
computable) via the conformal anomaly, and their smallness turns out to be
directly related to the smallness of the masses of light neutrinos.Comment: 10 pages, 2 figures, expanded version, to be published in EPJ
Leptogenesis Bound on Spontaneous Symmetry Breaking of Global Lepton Number
We propose a new class of leptogenesis bounds on the spontaneous symmetry
breaking of global lepton number. These models have a generic feature of
inducing new lepton number violating interactions, due to the presence of the
Majorons. We analyzed the singlet Majoron model with right-handed neutrinos and
find that the lepton number should be broken above 10^5 GeV to realize a
successful leptogenesis because the annihilations of the right-handed neutrinos
into the massless Majorons and into the standard model Higgs should go out of
equilibrium before the sphaleron process is over. We then argue that this type
of leptogenesis constraint should exist in the singlet-triplet Majoron models
as well as in a class of R-parity violating supersymmetric Majoron models.Comment: 4 pages, 2 figure
Possible Z-width probe of a "brane-world" scenario for neutrino masses
The possibility that the accurately known value of the Z width might furnish
information about the coupling of two neutrinos to the Majoron (Nambu-Goldstone
boson of spontaneous lepton number violation) is proposed and investigated in
detail. Both the "ordinary" case and the case in which one adopts a "brane"
world picture with the Majoron free to travel in extra dimensions are studied.
Bounds on the dimensionless coupling constants are obtained, allowing for any
number of extra dimensions and any intrinsic mass scale. These bounds may be
applied to a variety of different Majoron models. If a technically natural
see-saw model is adopted, the predicted coupling constants are far below these
upper bounds. In addition, for this natural model, the effect of extra
dimensions is to decrease the predicted partial Z width, the increase due to
many Kaluza-Klein excitations being compensated by the decrease of their common
coupling constant.Comment: RevTeX, 12 pages, 3 figure
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