410 research outputs found
The Superpartner Spectrum of Gaugino Mediation
We compute the superpartner masses in a class of models with gaugino
mediation (or no-scale) boundary conditions at a scale between the GUT and
Planck scales. These models are compelling because they are simple, solve the
supersymmetric flavor and CP problems, satisfy all constraints from colliders
and cosmology, and predict the superpartner masses in terms of very few
parameters. Our analysis includes the renormalization group evolution of the
soft-breaking terms above the GUT scale. We show that the running above the GUT
scale is largely model independent and find that a phenomenologically viable
spectrum is obtained.Comment: 15 page
Doublet-Triplet Splitting and Fermion Masses with Extra Dimensions
The pseudo-Goldstone boson mechanism for the ``doublet-triplet splitting''
problem of the grand unified theory can be naturally implemented in the
scenario with extra dimensions and branes. The two SU(6) global symmetries of
the Higgs sector are located on two separate branes while the SU(6) gauge
symmetry is in the bulk. After including several vector-like fields in the
bulk, and allowing the most general interactions with their natural strength
(including the higher dimensional ones which may be generated by gravity) which
are consistent with the geometry, a realistic pattern of the Standard Model
fermion masses and mixings can be naturally obtained without any flavor
symmetry. Neutrino masses and mixings required for the solar and atmospheric
neutrino problems can also be accommodated. The geometry of extra dimensions
and branes provides another way to realize the absence of certain interactions
(as required in the pseudo-Goldstone boson mechanism) or the smallness of some
couplings (e.g., the Yukawa couplings between the fermions and the Higgs
bosons), in addition to the usual symmetry arguments.Comment: 16 pages, 4 figures, LaTeX, references and some clarifying remarks
added, to be published in Phys. Rev.
Neutrino Masses in Flipped SU(5)
We analyse the fermion masses and mixings in the flipped SU(5) model. The
fermion mass matrices are evolved from the GUT scale down to by solving
the renormalization group equations for the Yukawa couplings. The constraints
imposed by the charged fermion data are then utilised to make predictions about
the neutrino properties . It is found that the {\it generalized } see-saw
mechanism which occurs naturally in this model can provide {\it i})a solution
to the solar neutrino problem via the MSW mechanism and {\it ii})a sufficiently
large mass to contribute as a hot dark matter component as
indicated by the recent COBE data.Comment: (14 Pages,No figures,TEX,IOA-290/92 preprint
Neutralino Decays at the CERN LHC
We study the distribution of lepton pairs from the second lightest neutralino
decay \tchi^0_2\to\tchi^0_1 l^+l^-. This decay mode is important to measure the
mass difference between \tchi^0_2 and the lightest neutralino \tchi^0_1, which
helps to determine the parameters of the minimal supersymmetric standard model
at the CERN LHC. We found that the decay distribution strongly depends on the
values of underlying MSSM parameters. For some extreme cases, the amplitude
near the end point of the lepton invariant mass distribution can be suppressed
so strongly that one needs the information of the whole m_{ll} distribution to
extract m_{\tchi^0_2}-m_{\tchi^0_1}. On the other hand, if systematic errors on
the acceptance can be controlled, this distribution can be used to constrain
slepton masses and the Z\tchi^0_2\tchi^0_1 coupling. Measurements of the
velocity distribution of \tchi^0_2 from samples near the end point of the
m_{ll} distribution, and of the asymmetry of the p_T of leptons, would be
useful to reduce the systematic errors.Comment: 23 pages, latex2e, 9 figures, minor change, accepted to PR
Twist-2 Heavy Flavor Contributions to the Structure Function
The twist--2 heavy flavor contributions to the polarized structure function
are calculated. We show that this part of is related
to the heavy flavor contribution to by the Wandzura--Wilczek
relation to all orders in the strong coupling constant. Numerical results are
presented.Comment: 17 pages LATEX, 1 style files, 4 figure
Positronium Portal into Hidden Sector: A new Experiment to Search for Mirror Dark Matter
The understanding of the origin of dark matter has great importance for
cosmology and particle physics. Several interesting extensions of the standard
model dealing with solution of this problem motivate the concept of hidden
sectors consisting of SU(3)xSU(2)_LxU(1)_Y singlet fields. Among these models,
the mirror matter model is certainly one of the most interesting. The model
explains the origin of parity violation in weak interactions, it could also
explain the baryon asymmetry of the Universe and provide a natural ground for
the explanation of dark matter. The mirror matter could have a portal to our
world through photon-mirror photon mixing (epsilon). This mixing would lead to
orthopositronium (o-Ps) to mirror orthopositronium oscillations, the
experimental signature of which is the apparently invisible decay of o-Ps. In
this paper, we describe an experiment to search for the decay o-Ps -> invisible
in vacuum by using a pulsed slow positron beam and a massive 4pi BGO crystal
calorimeter. The developed high efficiency positron tagging system, the low
calorimeter energy threshold and high hermiticity allow the expected
sensitivity in mixing strength to be epsilon about 10^-9, which is more than
one order of magnitude below the current Big Bang Nucleosynthesis limit and in
a region of parameter space of great theoretical and phenomenological interest.
The vacuum experiment with such sensitivity is particularly timely in light of
the recent DAMA/LIBRA observations of the annual modulation signal consistent
with a mirror type dark matter interpretation.Comment: 40 pages, 29 Figures 2 Tables v2: Ref. added, Fig. 29 and some text
added to explain idea for backscattering e+ background suppression, corrected
typos v3: minor corrections: Eq 2.1 corrected (6 lines-> 5 lines), Eq.2.17:
two extra "-" signs remove
Supersymmetric Unification Without Low Energy Supersymmetry And Signatures for Fine-Tuning at the LHC
The cosmological constant problem is a failure of naturalness and suggests
that a fine-tuning mechanism is at work, which may also address the hierarchy
problem. An example -- supported by Weinberg's successful prediction of the
cosmological constant -- is the potentially vast landscape of vacua in string
theory, where the existence of galaxies and atoms is promoted to a vacuum
selection criterion. Then, low energy SUSY becomes unnecessary, and
supersymmetry -- if present in the fundamental theory -- can be broken near the
unification scale. All the scalars of the supersymmetric standard model become
ultraheavy, except for a single finely tuned Higgs. Yet, the fermions of the
supersymmetric standard model can remain light, protected by chiral symmetry,
and account for the successful unification of gauge couplings. This framework
removes all the difficulties of the SSM: the absence of a light Higgs and
sparticles, dimension five proton decay, SUSY flavor and CP problems, and the
cosmological gravitino and moduli problems. High-scale SUSY breaking raises the
mass of the light Higgs to about 120-150 GeV. The gluino is strikingly long
lived, and a measurement of its lifetime can determine the ultraheavy scalar
mass scale. Measuring the four Yukawa couplings of the Higgs to the gauginos
and higgsinos precisely tests for high-scale SUSY. These ideas, if confirmed,
will demonstrate that supersymmetry is present but irrelevant for the hierarchy
problem -- just as it has been irrelevant for the cosmological constant problem
-- strongly suggesting the existence of a fine-tuning mechanism in nature.Comment: Typos and equations fixed, references adde
Fermion Masses and Coupling Unification in E6. Life in the Desert
We present an Grand Unified model with a realistic pattern of fermion
masses. All standard model fermions are unified in three fundamental 27-plets
(i.e. supersymmetry is not invoked), which involve in addition right handed
neutrinos and three families of vector like heavy quarks and leptons. The
lightest of those can lie in the low TeV range, being accessible to future
collider experiments. Due to the high symmetry, the masses and mixings of all
fermions are closely related. The new heavy fermions play a crucial role for
the quark and lepton mass matrices and the bilarge neutrino oscillations. In
all channels generation mixing and violation arise from a single
antisymmetric matrix. The breaking proceeds via an intermediate energy
region with SU(3)_L\tm SU(3)_R\tm SU(3)_C gauge symmetry and a discrete
left-right symmetry. This breaking pattern leads in a straightforward way to
the unification of the three gauge coupling constants at high scales, providing
for a long proton lifetime. The model also provides for the unification of the
top, bottom and tau Yukawa couplings and for new interesting relations in
flavor and generation space.Comment: RevTex4, three ps figures, some correction
Flavordynamics with Conformal Matter and Gauge Theories on Compact Hyperbolic Manifolds in Extra Dimensions
We outline a toy model in which a unique mechanism may trigger a dynamical
chain resulting in key low-energy regularities. The starting points are a
negative cosmological term in the bulk and conformally invariant nongravity
sector. These elements ensure compactification of the extra dimensional space
on a compact hyperbolic manifold (with the negative and constant scalar
curvature). The overall geometry is then M_4 x B_n. The negative curvature on
B_n triggers the formation of the four-dimensional defect which provides in
turn a dynamical localization of ordinary particles. It also leads,
simultaneously, to a spontaneous breaking of gauge symmetry through a Higgs
mechanism. Masses of the fermions, gauge bosons and scalars all derive from the
curvature of the internal manifold such that the Higgs boson is generally
heavier than the gauge bosons. The factorizable geometry M_4 x B_n and flatness
of M_4 require fine-tuning.Comment: 16 pp, added references and a figure with improvements in text;
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