553 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
Soft SUSY breaking contributions to proton decay
We show that in supersymmetric grand unified theories new effective D=4 and
D=5 operators for proton decay are induced by soft SUSY-breaking terms, when
heavy GUT gauge bosons are integrated out, in addition to the standard D=6
ones. As a result, the proton lifetime in gauge mediated channels can be
enhanced or even suppressed depending on the size of the heavy Higgses soft
terms.Comment: 16 pages, 2 figures, LaTeX, JHEP3 class, axodra
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
SU(3) Family Gauge Symmetry and the Axion
We analyze the structure of a recently proposed effective field theory (EFT)
for the generation of quark and lepton mass ratios and mixing angles, based on
the spontaneous breaking of an SU(3) family gauge symmetry at a high scale F.
We classify the Yukawa operators necessary to seed the masses, making use of
the continuous global symmetries that they preserve. One global U(1), in
addition to baryon number and electroweak hypercharge, remains unbroken after
the inclusion of all operators required by standard-model-fermion
phenomenology. An associated vacuum symmetry insures the vanishing of the
first-family quark and charged-lepton masses in the absence of the family gauge
interaction. If this U(1) symmetry is taken to be exact in the EFT, broken
explicitly by only the QCD-induced anomaly, and if the breaking scale F is
taken to lie in the range 10 to 9 - 10 to 12 GeV, then the associated
Nambu-Goldstone boson is a potential QCD axion.Comment: References added and clarifications in Vacuum Structure sectio
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.
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
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
Mirror World, Supersymmetric Axion and Gamma Ray Bursts
A modification of the relation between axion mass and the PQ constant permits
a relaxation of the astrophysical constraints, considerably enlarging the
allowed axion parameter space. We develop this idea in this paper, discussing a
model for an {\it ultramassive} axion, which essentially represents a
supersymmetric Weinberg-Wilczek axion of the mirror world. The experimental and
astrophysical limits allow a PQ scale f_a ~ 10^4-10^6 GeV and a mass m_a ~
1MeV, which can be accessible for future experiments.
On a phenomenological ground, such an {\it ultramassive} axion turns out to
be quite interesting. It can be produced during the gravitational collapse or
during the merging of two compact objects, and its subsequent decay into e+e-
provides an efficient mechanism for the transfer of the gravitational energy of
the collapsing system to the electron-positron plasma. This could resolve the
energy budget problem in the Gamma Ray Bursts and also help in understanding
the SN type II explosion phenomena.Comment: 20 pages, 5 eps figures, added footnote and reference
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
Anomalous U(1) symmetry and missing doublet SU(5) model
We present the supersymmetric models which provide a simple ``all
order'' solution to the doublet-triplet splitting problem through the missing
doublet mechanism. The crucial role is played by the anomalous gauge
symmetry and no additional discrete or global symmetries are needed.
Remarkably, such models can be realized even if the 75-plet Higgs is replaced
by the standard 24-plet. The same symmetry can also guarantee an exact
or approximate conservation of R parity, by suppressing the B and L violating
operators to the needed level. The neutrino masses and the proton decay via
operators are also examined. We also extend the model by incorporating
as a horizontal symmetry for explaining the fermion mass and mixing
hierarchy. Interestingly, in this scheme the necessary mild violation of the
troublesome degeneracy between the down quark and the charged lepton
masses can be induced by certain R-parity violating operators.Comment: 16 pages, LATEX, no figure
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