18 research outputs found
Orbifold Reduction Of The Quark-Lepton Symmetric Model
We investigate the quark-lepton symmetric gauge group in five dimensions,
with the gauge symmetry broken by a combination of orbifold compactification of
the extra dimension and the Higgs mechanism. The gauge sector of the model is
investigated and contrasted with the four dimensional case. We obtain lower
bounds on the mass of the exotic gauge bosons, the inverse compactification
scale and the exotic leptons. Light neutrinos are obtained without requiring
any scale larger than a TeV. However an ultra-violet cut-off of order
GeV is required to suppress proton decay inducing non-renormalizable operators.Comment: References added to match PRD versio
Suppressing Proton Decay By Separating Quarks And Leptons
Arkani-Hamed and Schmaltz (AS) have shown that proton stability need not
originate from symmetries in a high energy theory. Instead the proton decay
rate is suppressed if quarks and leptons are spatially separated in a compact
extra dimension. This separation may be achieved by coupling five dimensional
fermions to a bulk scalar field with a non-trivial vacuum profile and requires
relationships between the associated quark and lepton Yukawa couplings. We
hypothesise that these relationships are the manifestation of an underlying
symmetry. We further show that the AS proposal may suggest that proton
stability \emph{is} the result of an underlying symmetry, though not
necessarily the traditional baryon number symmetry.Comment: 4 pages, references added to match published versio
Systematic Study Of Leptonic Mixing In A Class Of SU_H(2) Models
We perform a systematic analysis of the PMNS matrices which arise when one
assigns the three generations of leptons to the representation of a
horizontal symmetry. This idea has been previously explored by
Kuchimanchi and Mohapatra. However, we assume the neutrino mass matrix
results from leptonic couplings to triplet scalar fields and
hierarchies exist amongst lepton mass matrix elements which result from
couplings to scalar fields with different charges. Of the sixteen
candidate PMNS matrices which result it is found that only one is both
predictive and possesses a leading order structure compatible with experimental
data. The relevant neutrino mass matrix displays the symmetry
to leading order and we explore the perturbations required
to produce a realistic lepton spectrum. The effective mass in neutrinoless
double beta decay is required to lie in the range
, which is just below current
experimental bounds. is non-zero but not uniquely determined.Comment: To appear in Phys. Rev.
Quark-Lepton Symmetry In Five Dimensions
We construct a complete five dimensional Quark-Lepton symmetric model, with
all fields propagating in the bulk. The extra dimension forms an orbifold with the zero mode fermions corresponding to standard model
quarks localised at one fixed point. Zero modes corresponding to
left(right)-chiral leptons are localised at (near) the other fixed point. This
localisation pattern is motivated by the symmetries of the model. Shifting the
right-handed neutrinos and charged leptons slightly from the fixed point
provides a new mechanism for understanding the absence of relations of the type
or in Quark-Lepton symmetric models. Flavour changing
neutral currents resulting from Kaluza Klein gluon exchange, which typically
arise in the quark sector of split fermion models, are suppressed due to the
localisation of quarks at one point. The separation of quarks and leptons in
the compact extra dimension also acts to suppress the proton decay rate. This
permits the extra dimension to be much larger than that obtained in a previous
construct, with the bound TeV obtained.Comment: 12 pages, references added to match published versio
(3+2) Neutrino Scheme From A Singular Double See-Saw Mechanism
We obtain a 3+2 neutrino spectrum within a left-right symmetric framework by
invoking a singular double see-saw mechanism. Higgs doublets are employed to
break and three additional fermions, singlets under the left-right
symmetric gauge group, are included. The introduction of a singularity into the
singlet fermion Majorana mass matrix results in a light neutrino sector of
three neutrinos containing predominantly , ,
separated from two neutrinos containing a small component. The
resulting active-sterile mixing in the mixing matrix is specified
once the mass eigenvalues and the submatrix corresponding to the MNS
mixing matrix are known.Comment: 5 pages, matches published versio
Radiative neutrino mass generation and dark energy
We study the models with radiative neutrino mass generation and explore the
relation between the neutrino masses and dark energy. In these models, the
pseudo-Nambu-Goldston bosons (pNGBs) arise at two-loop level via the Majorana
neutrino masses. In particular, we demonstrate that the potential energy of the
pNGB can be the dark energy potential and the observed value of the equation of
state (EoS) parameter of the universe, , , can be realized.Comment: 10 pages, 1 figure, a minor correction in Eq. (17
Relic neutrino asymmetry evolution from first principles
The exact Quantum Kinetic Equations for a two-flavour active-sterile neutrino
system are used to provide a systematic derivation of approximate evolution
equations for the relic neutrino asymmetry. An extension of the adiabatic
approximation for matter-affected neutrino oscillations is developed which
incorporates decoherence due to collisions. Exact and approximate expressions
for the decoherence and repopulation functions are discussed. A first pass is
made over the exact treatment of multi-flavour partially incoherent
oscillations.Comment: RevTeX, 38 pages, crucial typos corrected; published versio