3,233 research outputs found
Gauged B-3L_\tau, low-energy unification and proton decay
We point out that if there is a gauged symmetry at low energy, it
can prevent fast proton decay. This may help building models with theories with
extra dimensions at the TeV scale. For purpose of illustration we present an
explicit model with large extra dimensions. The Higgs required for a realistic
fermion masses and mixing are included. The problem of neutrino masses are
solved with triplet Higgs scalars. The proton remains stable even after the
symmetry breaking.Comment: 8 pages, Late
Light Sterile Neutrinos from Large Extra Dimensions
An experimentally verifiable Higgs-triplet model of neutrino masses from
large extra dimensions was recently proposed. We extend it to accomodate a
light sterile neutrino which also mixes with the three active neutrinos. A
previously proposed phenomenological model of four neutrinos (\underline {the
only viable such model now left}, in view of the latest atmospheric and solar
neutrino-oscillation data) is specifically realized.Comment: 10 pages, no figure, remarks and references adde
Efficacious Additions to the Standard Model
If split supersymmetry can be advocated as a means to have gauge-coupling
unification as well as dark matter, another plausible scenario is to enlarge
judiciously the particle content of the Standard Model to achieve the same
goals without supersymmetry. A simple efficacious example is presented.Comment: 6 pages, no figure, one reference added, version to appear in PL
Phenomenology of the Neutrino-Mass-Giving Higgs Triplet and the Low-Energy Seesaw Violation of Lepton Number
Small realistic Majorana neutrino masses can be generated via a Higgs triplet
without having energy scales larger than TeV in the theory. The large effective mass scale in the
well-known seesaw neutrino-mass operator is
naturally obtained with where is a {\it small}
scale of lepton-number violation. In theories with large extra dimensions, the
smallness of is naturally obtained by the mechanism of ``shining'' if the
number of extra dimensions We study here the Higgs phenomenology of
this model, where the spontaneous violation of lepton number is treated as an
external source from extra dimensions. The observable decays will determine directly the magnitudes of the elements of
the neutrino mass matrix. The decays and ,
where is the massless Goldstone boson (Majoron), are also possible, but
of special importance is the decay which provides stringent
constraints on the allowed parameter space of this model. Based on the current
neutrino data, we also predict observable rates of conversion in
nuclei.Comment: Minor changes in the text, results unchange
Low-Scale Axion from Large Extra Dimensions
The mass of the axion and its decay rate are known to depend only on the
scale of Peccei-Quinn symmetry breaking, which is constrained by astrophysics
and cosmology to be between and GeV. We propose a new
mechanism such that this effective scale is preserved and yet the fundamental
breaking scale of is very small (a kind of inverse seesaw) in the
context of large extra dimensions with an anomalous U(1) gauge symmetry in our
brane. Unlike any other (invisible) axion model, there are now possible
collider signatures in this scenario.Comment: 11 pages, no figur
Majorana neutrinos with split fermions in extra dimensions
We propose new solutions to the neutrino mass problem in theories with large
extra dimensions in a thick wall scenario. It has recently been argued that our
3-brane could be a thick wall at the boundary of the bulk. The gauge bosons and
the Higgs scalars have an almost flat profile on this wall, while fermions
could have localized profile with left-handed and right-handed components
displaced with respect to each other. We point out that with split fermions it
is possible to generate Majorana neutrino masses contributing to the
neutrinoless double beta decay. The almost degenerate neutrinos can also come
out naturally in this case. Unlike other models of neutrino masses in extra
dimensions there are no bulk fields in this scenario.Comment: 12 pages, 1 figure, revise
Naturally Light Neutrinos and Unification in Theories with Low Scale Quantum Gravity
Within low scale theories traditional see-saw and scalar triplet mechanisms,
for neutrino mass suppression, do not work out anymore and for realistic model
building some new ideas are needed. In this paper we suggest mechanism,
different from existing ones, which provides natural suppression of the
neutrino masses. The mechanism is realized through extended scalars of 4, 5 or
6 dimensional multiplets. Scenario, with fundamental mass scale
in a TeV range, requires 4-plets guaranteeing neutrino masses
eV. For theories with TeV 5-plets
should be involved, while in scenarios with few TeV, 6-plets could be
efficient.
The considered mechanism could be successfully applied also for
supersymmetric theories, building scenarios with various values of low .
Within considered models we also address the question of gauge coupling
unification. For low scale unification, existence of compact extra dimensions
turns out to be crucial. Due to additional scalar multiplets, some new examples
of unification are found for both - non SUSY and SUSY cases. Within non SUSY
scenarios introduced scalars take advantage and are important for
successful unification.Comment: LaTex, 1 eps figure, discussions and references adde
Tribimaximal Neutrino Mixing from A_4 Replication
Motivated by dimensional deconstruction, we propose a model of tribimaximal
neutrino mixing based on A_4 x A_4 symmetry. In this model, the two triplet
symmetry-breaking fields of conventional A_4 models are taken to transform
under different A_4 group factors, but are not distinguished by any other
quantum numbers. An additional bi-triplet flavon field breaks A_4 x A_4 to its
diagonal subgroup. If the bi-triplet transforms under an additional Z_3
symmetry, we show that one can construct a general, renormalizable
superpotential that yields the desired pattern of symmetry breaking. We
identify the features that this model has in common with a deconstructed 5D
theory in which A_4 is a subgroup of a continuous gauged flavor symmetry in the
bulk.Comment: 13 pages LaTeX (v2: discussion added
Computational search for ultrasmall and fast skyrmions in the Inverse Heusler family
Skyrmions are magnetic excitations that are potentially ultrasmall and
topologically protected, making them interesting for high-density
all-electronic ultrafast storage applications. While recent experiments have
confirmed the existence of various types of skyrmions, their typical sizes are
much larger than traditional domain walls, except at very low temperature. In
this work, we explore the optimal material parameters for hosting ultra-small,
fast, and room temperature stable skyrmions. As concrete examples, we explore
potential candidates from the inverse Heusler family. Using first-principles
calculations of structural and magnetic properties, we identify several
promising ferrimagnetic inverse Heusler half-metal/near half-metals and analyze
their phase space for size and metastability.Comment: 7 pages, 3 figures, 1 tabl
A note on two-loop effects in the DMSSM
We investigate the proposed ``D-brane alternative'' to the MSSM model (DMSSM)
which is a type II B string orientifold model with N=1 supersymmetry, three
generations and a gauge
group. An accurate analysis at two-loop level is performed to show that
unification constraints predict a ``left-right'' symmetry breaking scale in the
TeV region. The exact value of this scale is the result of the competing
effects of the two loop terms against the low energy supersymmetric threshold
effects. The model accommodates logarithmic unification of the gauge couplings
at an intermediate scale of GeV and the necessary conditions to
achieve this are addressed.Comment: 10 pages, 6 figures, LaTe
- âŠ