337 research outputs found
A New Approach to Flavor Symmetry and an Extended Naturalness Principle
A class of non-supersymmetric extensions of the Standard Model is proposed in
which there is a multiplicity of light scalar doublets in a multiplet of a
non-abelian family group with the Standard Model Higgs doublet. Anthropic
tuning makes the latter light, and consequently the other scalar doublets
remain light because of the family symmetry. The family symmetry greatly
constrains the pattern of FCNC and proton decay operators coming from
scalar-exchange. Such models show that useful constraints on model-building can
come from an extended naturalness principle when the electroweak scale is
anthropically tuned.Comment: 31 pages, 3 figure
Nucleon-Nucleon Bremsstrahlung emission of massive Axion
We consider the problem of axion production by bremsstrahlung emission in a
nuclear medium. The usual assumption of a massless axion is replaced by more
general hypotheses, so that we can describe the emission process for axions
with mass up to a few MeV. We point out that in certain physical situations the
contribution from non-zero mass is non-negligible. In particular, in the
mechanism for the production of Gamma Ray Bursts via emission of heavy axions
the axion mass m_a ~ 1MeV is comparable with the temperature of the nuclear
medium and thus can not be disregarded. Looking at our results we find, in
fact, a fairly considerable reduction of the axion luminosity in that
mechanism.Comment: 16 pages, 5 figure
The Super-little Higgs
Supersymmetry combined with little-Higgs can render the Higgs vev
super-little, providing models of electroweak symmetry breaking free from
fine-tunings. We discuss the difficulties that arise in implementing this idea
and propose one simple successful model. Thanks to appropriately chosen Higgs
representations, D-terms give no tree-level mass term to the Goldstone. The
fermion representations are anomaly free, generation independent and embeddable
into an SU(6) GUT. A simple mechanism provides the large top quark mass.Comment: Additional mechanism to get a quartic coupling discussed. References
adde
A Light Supersymmetric Axion in an Anomalous Abelian Extension of the Standard Model
We present a supersymmetric extension of the Standard Model (USSM-A) with an
anomalous U(1) and Stueckelberg axions for anomaly cancellation, generalizing
similar non-supersymmetric constructions. The model, built by a bottom-up
approach, is expected to capture the low-energy supersymmetric description of
axionic symmetries in theories with gauged anomalous abelian interactions,
previously explored in the non-supersymmetric case for scenarios with
intersecting branes. The choice of a USSM-like superpotential, with one extra
singlet superfield and an extra abelian symmetry, allows a physical axion-like
particle in the spectrum. We describe some general features of this
construction and in particular the modification of the dark-matter sector which
involves both the axion and several neutralinos with an axino component. The
axion is expected to be very light in the absence of phases in the
superpotential but could acquire a mass which can also be in the few GeV range
or larger. In particular, the gauging of the anomalous symmetry allows
independent mass/coupling interaction to the gauge fields of this particle, a
feature which is absent in traditional (invisible) axion models. We comment on
the general implications of our study for the signature of moduli from string
theory due to the presence of these anomalous symmetries.Comment: 46 pages, 28 figures. Revised version, accepted for a publication on
Phys.Rev.
Neutrinos and SU(3) Family Gauge Symmetry
We include the standard-model (SM) leptons in a recently proposed framework
for the generation of quark mass ratios and Cabibbo-Kobayashi-Maskawa (CKM)
mixing angles from an SU(3) family gauge interaction. The set of SM-singlet
scalar fields describing the spontaneous breaking is the same as employed for
the quark sector. The imposition at tree-level of the experimentally correct
Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix, in the form of a tri-bi
maximal structure, fixes several of the otherwise free parameters and renders
the model predictive. The normal hierarchy among the neutrino masses emerges
from this scheme.Comment: 9 pages, 3 tables; a comment added to clarify the effects of
additional Yukawa operators; final version in PR
Twin SUSY
We construct an extension of the MSSM in which superpartners can naturally be
heavier than the electroweak scale. This ``little hierarchy'' of scales is
stable because the Higgs arises as a pseudo-Nambu-Goldstone boson in the
breaking of an accidental SU(4) symmetry of the Higgs sector. Supersymmetry and
the global symmetry combine to forbid logarithmically divergent one-loop
contributions to the Higgs mass. The accidental symmetry follows from a simple
``twin'' parity which exchanges the SU(2) sectors in the SU(3)_C x SU(2)_L x
SU(2)_R x U(1)_X gauge group.Comment: 10 pages; v2: references and Lawrence adde
Multi-Component Dark Matter Systems and Their Observation Prospects
Conversions and semi-annihilations of dark matter (DM) particles in addition
to the standard DM annihilations are considered in a three-component DM system.
We find that the relic abundance of DM can be very sensitive to these
non-standard DM annihilation processes, which has been recently found for
two-component DM systems. To consider a concrete model of a three-component DM
system, we extend the radiative seesaw model of Ma by adding a Majorana fermion
\chi and a real scalar boson \phi, to obtain a Z_2 \times Z'_2 DM stabilizing
symmetry, where we assume that the DM particles are the inert Higgs boson, \chi
and \phi. It is shown how the allowed parameter space, obtained previously in
the absence of \chi and \phi, changes. The semi-annihilation process in this
model produces monochromatic neutrinos. The observation rate of these
monochromatic neutrinos from the Sun at IceCube is estimated. Observations of
high energy monochromatic neutrinos from the Sun may indicate a multi-component
DM system.Comment: 27 pages, 11 figure
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