63 research outputs found
Linear Collider Capabilities for Supersymmetry in Dark Matter Allowed Regions of the mSUGRA Model
Recent comparisons of minimal supergravity (mSUGRA) model predictions with
WMAP measurements of the neutralino relic density point to preferred regions of
model parameter space. We investigate the reach of linear colliders (LC) with
and 1 TeV for SUSY in the framework of the mSUGRA model. We find
that LCs can cover the entire stau co-annihilation region provided \tan\beta
\alt 30. In the hyperbolic branch/focus point (HB/FP) region of parameter
space, specialized cuts are suggested to increase the reach in this important
``dark matter allowed'' area. In the case of the HB/FP region, the reach of a
LC extends well past the reach of the CERN LHC. We examine a case study in the
HB/FP region, and show that the MSSM parameters and can be
sufficiently well-measured to demonstrate that one would indeed be in the HB/FP
region, where the lightest chargino and neutralino have a substantial higgsino
component.Comment: 29 pages, 15 EPS figures; updated version slightly modified to
conform with published versio
Super-conservative interpretation of muon g-2 results applied to supersymmetry
The recent developments in theory and experiment related to the anomalous
magnetic moment of the muon are applied to supersymmetry. We follow a very
cautious course, demanding that the supersymmetric contributions fit within
five standard deviations of the difference between experiment and the standard
model prediction. Arbitrarily small supersymmetric contributions are then
allowed, so no upper bounds on superpartner masses result. Nevertheless,
non-trivial exclusions are found. We characterize the substantial region of
parameter space ruled out by this analysis that has not been probed by any
previous experiment. We also discuss some implications of the results for
forthcoming collider experiments.Comment: 10 pages, latex, 3 fig
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
On Yukawa quasi-unification with mu<0
Although recent data on the muon anomalous magnetic moment strongly disfavor
the constrained minimal supersymmetric standard model with mu<0, they cannot
exclude it because of theoretical ambiguities. We consider this model
supplemented by a Yukawa quasi-unification condition which allows an acceptable
b-quark mass. We find that the cosmological upper bound on the lightest
sparticle relic abundance is incompatible with the data on the branching ratio
of b-->s gamma, which is evaluated by including all the next-to-leading order
corrections. Thus, this scheme is not viable.Comment: 4 pages including 3 figures, Revte
Probing mSUGRA via the Extreme Universe Space Observatory
An analysis is carried out within mSUGRA of the estimated number of events
originating from upward moving ultra-high energy neutralinos that could be
detected by the Extreme Universe Space Observatory (EUSO). The analysis
exploits a recently proposed technique that differentiates ultra-high energy
neutralinos from ultra-high energy neutrinos using their different absorption
lengths in the Earth's crust. It is shown that for a significant part of the
parameter space, where the neutralino is mostly a Bino and with squark mass
TeV, EUSO could see ultra-high energy neutralino events with
essentially no background. In the energy range 10^9 GeV < E < 10^11 GeV, the
unprecedented aperture of EUSO makes the telescope sensitive to neutralino
fluxes as low as 1.1 \times 10^{-6} (E/GeV)^{-1.3} GeV^{-1} cm^{-2} yr^{-1}
sr^{-1}, at the 95% CL. Such a hard spectrum is characteristic of supermassive
particles' -body hadronic decay. The case in which the flux of ultra-high
energy neutralinos is produced via decay of metastable heavy particles with
uniform distribution throughout the universe is analyzed in detail. The
normalization of the ratio of the relics' density to their lifetime has been
fixed so that the baryon flux produced in the supermassive particle decays
contributes to about 1/3 of the events reported by the AGASA Collaboration
below 10^{11} GeV, and hence the associated GeV gamma-ray flux is in complete
agreement with EGRET data. For this particular case, EUSO will collect between
4 and 5 neutralino events (with 0.3 of background) in ~ 3 yr of running. NASA's
planned mission, the Orbiting Wide-angle Light-collectors (OWL), is also
briefly discussed in this context.Comment: Some discussion added, final version to be published in Physical
Review
Focus Point SUSY at the LHC Revisited
The estimation of the backgrounds for gluino signals in focus point
supersymmetry is extended by including the backgrounds from the production of
four third generation quarks in the analysis. We find that these backgrounds
are negligible if one uses the strong selection criteria proposed in the
literature (including this analysis) for heavy gluino searches. Softer
selection criteria often recommended for lighter gluino searches yield
backgrounds which are small but numerically significant. We have also repeated
the more conventional background calculations and compared our results with the
other groups. We find that the size of the total residual background estimated
by different groups using different event generators and hard kinematical cuts
agree approximately. In view of the theoretical uncertainties in the leading
order signal and background cross sections mainly due to the choice of the QCD
scale, the gluino mass reach at the LHC cannot be pinpointed. However,
requiring a signal with tagged b-jets (instead of the standard
choice of ) it is shown that gluino masses close to 2 TeV can be
probed at the LHC for a range of reasonable choices of the QCD scale for an
integrated luminosity of 300 fb.Comment: 17 pages, 4 figures, minor typos correctio
Particle Physics Approach to Dark Matter
We review the main proposals of particle physics for the composition of the
cold dark matter in the universe. Strong axion contribution to cold dark matter
is not favored if the Peccei-Quinn field emerges with non-zero value at the end
of inflation and the inflationary scale is superheavy since, under these
circumstances, it leads to unacceptably large isocurvature perturbations. The
lightest neutralino is the most popular candidate constituent of cold dark
matter. Its relic abundance in the constrained minimal supersymmetric standard
model can be reduced to acceptable values by pole annihilation of neutralinos
or neutralino-stau coannihilation. Axinos can also contribute to cold dark
matter provided that the reheat temperature is adequately low. Gravitinos can
constitute the cold dark matter only in limited regions of the parameter space.
We present a supersymmetric grand unified model leading to violation of Yukawa
unification and, thus, allowing an acceptable b-quark mass within the
constrained minimal supersymmetric standard model with mu>0. The model
possesses a wide range of parameters consistent with the data on the cold dark
matter abundance as well as other phenomenological constraints. Also, it leads
to a new version of shifted hybrid inflation.Comment: 32 pages including 6 figures, uses svmult.cls, some clarifications
added, lectures given at the Third Aegean Summer School "The Invisible
Universe: Dark Matter and Dark Energy", 26 September-1 October 2005, Karfas,
Island of Chios, Greece (to appear in the proceedings
Implications of the Muon Anomalous Magnetic Moment for Supersymmetry
We re-examine the bounds on supersymmetric particle masses in light of the
E821 data on the muon anomalous magnetic moment. We confirm, extend and
supersede previous bounds. In particular we find (at one sigma) no lower limit
on tan(beta) or upper limit on the chargino mass implied by the data at
present, but at least 4 sparticles must be lighter than 700 to 820 GeV and at
least one sparticle must be lighter than 345 to 440 GeV. However, the E821
central value bounds tan(beta) > 4.7 and the lighter chargino mass by 690 GeV.
For tan(beta) < 10, the data indicates a high probability for direct discovery
of SUSY at Run II or III of the Tevatron.Comment: 20 pages LaTeX, 14 figures; references adde
Relic Neutralino Densities and Detection Rates with Nonuniversal Gaugino Masses
We extend previous analyses on the interplay between nonuniversalities in the
gaugino mass sector and the thermal relic densities of LSP neutralinos, in
particular to the case of moderate to large tan beta. We introduce a set of
parameters that generalizes the standard unified scenario to cover the complete
allowed parameter space in the gaugino mass sector. We discuss the physical
significance of the cosmologically preferred degree of degeneracy between
charginos and the LSP and study the effect this degree of degeneracy has on the
prospects for direct detection of relic neutralinos in the next round of dark
matter detection experiments. Lastly, we compare the fine tuning required to
achieve a satisfactory relic density with the case of universal gaugino masses,
as in minimal supergravity, and find it to be of a similar magnitude. The
sensitivity of quantifiable measures of fine-tuning on such factors as the
gluino mass and top and bottom masses is also examined.Comment: Uses RevTeX; 14 pages, 16 figure
Supersymmetric Benchmarks with Non-Universal Scalar Masses or Gravitino Dark Matter
We propose and examine a new set of benchmark supersymmetric scenarios, some
of which have non-universal Higgs scalar masses (NUHM) and others have
gravitino dark matter (GDM). The scalar masses in these models are either
considerably larger or smaller than the narrow range allowed for the same
gaugino mass m_{1/2} in the constrained MSSM (CMSSM) with universal scalar
masses m_0 and neutralino dark matter. The NUHM and GDM models with larger m_0
may have large branching ratios for Higgs and/or production in the cascade
decays of heavier sparticles, whose detection we discuss. The phenomenology of
the GDM models depends on the nature of the next-to-lightest supersymmetric
particle (NLSP), which has a lifetime exceeding 10^4 seconds in the proposed
benchmark scenarios. In one GDM scenario the NLSP is the lightest neutralino
\chi, and the supersymmetric collider signatures are similar to those in
previous CMSSM benchmarks, but with a distinctive spectrum. In the other GDM
scenarios based on minimal supergravity (mSUGRA), the NLSP is the lighter stau
slepton {\tilde \tau}_1, with a lifetime between ~ 10^4 and 3 X 10^6 seconds.
Every supersymmetric cascade would end in a {\tilde \tau}_1, which would have a
distinctive time-of-flight signature. Slow-moving {\tilde \tau}_1's might be
trapped in a collider detector or outside it, and the preferred detection
strategy would depend on the {\tilde \tau}_1 lifetime. We discuss the extent to
which these mSUGRA GDM scenarios could be distinguished from gauge-mediated
models.Comment: 52 pages LaTeX, 13 figure
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