176 research outputs found
The Reach of the Fermilab Tevatron and CERN LHC for Gaugino Mediated SUSY Breaking Models
In supersymmetric models with gaugino mediated SUSY breaking (inoMSB), it is
assumed that SUSY breaking on a hidden brane is communicated to the visible
brane via gauge superfields which propagate in the bulk. This leads to GUT
models where the common gaugino mass is the only soft SUSY breaking
term to receive contributions at tree level. To obtain a viable phenomenology,
it is assumed that the gaugino mass is induced at some scale beyond the
GUT scale, and that additional renormalization group running takes place
between and as in a SUSY GUT. We assume an SU(5) SUSY GUT above
the GUT scale, and compute the SUSY particle spectrum expected in models with
inoMSB. We use the Monte Carlo program ISAJET to simulate signals within the
inoMSB model, and compute the SUSY reach including cuts and triggers approriate
to Fermilab Tevatron and CERN LHC experiments. We find no reach for SUSY by the
Tevatron collider in the trilepton channel. %either with or without %identified
tau leptons. At the CERN LHC, values of (1160) GeV can be probed
with 10 (100) fb of integrated luminosity, corresponding to a reach in
terms of of 2150 (2500) GeV. The inoMSB model and mSUGRA can likely
only be differentiated at a linear collider with sufficient energy to
produce sleptons and charginos.Comment: 17 page revtex file with 9 PS figure
Neutralino relic density in supersymmetric GUTs with no-scale boundary conditions above the unification scale
We investigate SU(5) and SO(10) GUTs with vanishing scalar masses and
trilinear scalar couplings at a scale higher than the unification scale. The
parameter space of the models, further constrained by b-\tau Yukawa coupling
unification, consists of a common gaugino mass and of \tan\beta. We analyze the
low energy phenomenology, finding that A-pole annihilations of neutralinos
and/or coannihilations with the lightest stau drive the relic density within
the cosmologically preferred range in a significant region of the allowed
parameter space. Implications for neutralino direct detection and for CERN LHC
experiments are also discussed.Comment: 14 pages, 5 figures, JHEP style. Version accepted for publication in
JHE
Deconstructing Gaugino Mediation
We present a model of supersymmetry breaking which produces gaugino masses
and negligible scalar masses at a high scale. The model is inspired by
``deconstructing'' or ``latticizing'' models in extra dimensions where
supersymmetry breaking and visible matter are spatially separated. We find a
simple four-dimensional model which only requires two lattice sites (or gauge
groups) to reproduce the phenomenology.Comment: LaTeX, 9 pages, acknowledgements adde
Accidental Supersymmetric Dark Matter and Baryogenesis
We show that "accidental" supersymmetry is a beyond-the-Standard Model
framework that naturally accommodates a thermal relic dark matter candidate and
successful electroweak baryogenesis, including the needed strongly first-order
character of the electroweak phase transition. We study the phenomenology of
this setup from the standpoint of both dark matter and baryogenesis. For
energies around the electroweak phase transition temperature, the low-energy
effective theory is similar to the MSSM with light super-partners of the
third-generation quarks and of the Higgs and gauge bosons. We calculate the
dark matter relic abundance and the baryon asymmetry across the accidental
supersymmetry parameter space, including resonant and non-resonant CP-violating
sources. We find that there are regions of parameter space producing both the
observed value of the baryon asymmetry and a dark matter candidate with the
correct relic density and conforming to present-day constraints from dark
matter searches. This scenario makes sharp predictions for the particle
spectrum, predicting a lightest neutralino mass between 200 and 500 GeV, with
all charginos and neutralinos within less than a factor 2 of the lightest
neutralino mass and the heavy Higgs sector within 20-25% of that mass, making
it an interesting target for collider searches. In addition, we demonstrate
that successful accidental supersymmetric dark matter and baryogenesis will be
conclusively tested with improvements smaller than one order of magnitude to
the current performance of electron electric dipole moment searches and of
direct dark matter searches, as well as with IceCube plus Deep Core neutrino
telescope data.Comment: 36 pages, 10 figure
Next-to-leading order QCD calculations with parton showers II: soft singularities
Programs that calculate observables in quantum chromodynamics at
next-to-leading order typically generate events that consist of partons rather
than hadrons -- and just a few partons at that. These programs would be much
more useful if the few partons were turned into parton showers, which could be
given to one of the Monte Carlo event generators to produce hadron showers. In
a previous paper, we have seen how to generate parton showers related to the
final state collinear singularities of the perturbative calculation for the
example of e+ + e- --> 3 jets. This paper discusses the treatment of the soft
singularities.Comment: 26 pages with 5 figures. This version is close to the version to be
publishe
Higgs-mediated leptonic decays of B_s and B_d mesons as probes of supersymmetry
If tan(beta) is large, down-type quark mass matrices and Yukawa couplings
cannot be simultaneously diagonalized, and flavour violating couplings of the
neutral Higgs bosons are induced at the 1-loop level. These couplings lead to
Higgs-mediated contributions to the decays B_s -> mu+ mu- and B_d -> tau+ tau-,
at a level that might be of interest for the current Tevatron run, or possibly,
at B-factories. We evaluate the branching ratios for these decays within the
framework of minimal gravity-, gauge- and anomaly-mediated SUSY breaking
models, and also in SU(5) supergravity models with non-universal gaugino mass
parameters at the GUT scale. We find that the contribution from gluino loops,
which seems to have been left out in recent phenomenological analyses, is
significant. We explore how the branching fraction varies in these models,
emphasizing parameter regions consistent with other observations.Comment: Revised to accommodate minor changes in original text and update
reference
Yukawa coupling unification and non-universal gaugino mediation of supersymmetry breaking
The requirement of Yukawa coupling unification highly constrains the SUSY
parameter space. In several SUSY breaking scenarios it is hard to reconcile
Yukawa coupling unification with experimental constraints from B(b->s gamma)
and the muon anomalous magnetic moment a_mu. We show that b-tau or even t-b-tau
Yukawa unification can be satisfied simultaneously with b->s gamma and a_mu in
the non-universal gaugino mediation scenario. Non-universal gaugino masses
naturally appear in higher dimensional grand unified models in which gauge
symmetry is broken by orbifold compactification. Relations between SUSY
contributions to fermion masses, b->s gamma and a_mu which are typical for
models with universal gaugino masses are relaxed. Consequently, these
phenomenological constraints can be satisfied simultaneously with a relatively
light SUSY spectrum, compared to models with universal gaugino masses.Comment: 20 pages, 8 figures. References added. A copy of the paper with
better resolution figures can be found at
http://www.hep.fsu.edu/~balazs/Physics/Papers/2003
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
Neutralino Dark Matter, b-tau Yukawa Unification and Non-Universal Sfermion Masses
We study the implications of minimal non-Universal Boundary Conditions in the
sfermion Soft SUSY Breaking (SSB) masses of mSUGRA. We impose asymptotic b-tau
Yukawa coupling Unification and we resort to a parameterization of the
deviation from Universality in the SSB motivated by the multiplet structure of
SU(5) GUT. A set of cosmo-phenomenological constraints, including the recent
results from WMAP, determines the allowed parameter space of the models under
consideration. We highlight a new coannihilation corridor where
neutralino-sbottom and neutralino-tau sneutrino-stau coannihilations
significantly contribute to the reduction of the neutralino relic density.Comment: 38 pages, 27 Figures, Latex; Version accepted for publication in PR
Slepton and Neutralino/Chargino Coannihilations in MSSM
Within the low-energy effective Minimal Supersymmetric extension of Standard
Model (effMSSM) we calculated the neutralino relic density taking into account
slepton-neutralino and neutralino-chargino/neutralino coannihilation channels.
We performed comparative study of these channels and obtained that both of them
give sizable contributions to the reduction of the relic density. Due to these
coannihilation processes some models (mostly with large neutralino masses)
enter into the cosmologically interesting region for relic density, but other
models leave this region. Nevertheless, in general, the predictions for direct
and indirect dark matter detection rates are not strongly affected by these
coannihilation channels in the effMSSM.Comment: 12 pages, 9 figures, revte
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