3,296 research outputs found
Probing the SUSY breaking scale at an collider
If supersymmetry is spontaneously at a low energy scale then the resulting
gravitino would be very light. The interaction strength of the longitudinal
components of such a light gravitino to electron-selectron pair then becomes
comparable to that of electroweak interactions. Such a light gravitino could
modify the cross-section for e^_L e^_R-->\tilde {e}_L\tilde {e}_R from its
MSSM value. Precision measurement of this cross-section could therefore be used
to probe the low energy SUSY breaking scale.Comment: Plain Tex, 7 pages, No figure
Anomaly-Free Gauged R-Symmetry
We review the gauging of an R-symmetry in local and global susy. We then
construct the first anomaly-free models. We break the R-symmetry and susy at
the Planck scale and discuss the low-energy effects. We include a solution to
the mu-problem, and the prediction of observable effects at HERA. The models
also nicely allow for GUT-scale baryogenesis and R-parity violation without the
sphaleron interactions erasing the baryon-asymmetry.Comment: 6 pages, latex, no figures. Talk presented at SUSY-95. Work done in
collaboration with A. Chamseddin
Light Neutralinos in B-Decays
We consider the decays of a -meson into a pair of lightest
supersymmetric particles (LSP) in the minimal supersymmetric standard model. It
is found that the parameter space for light LSP's in the range of 1 GeV can be
appreciably constrained by looking for such decays.Comment: 9 pages, LaTex, 2 figures (hard copies of the figures available from
the Authors on request
The Supersymmetric Particle Spectrum
We examine the spectrum of supersymmetric particles predicted by grand
unified theoretical (GUT) models where the electroweak symmetry breaking is
accomplished radiatively. We evolve the soft supersymmetry breaking parameters
according to the renormalization group equations (RGE). The minimization of the
Higgs potential is conveniently described by means of tadpole diagrams. We
present complete one-loop expressions for these minimization conditions,
including contributions from the matter and the gauge sectors. We concentrate
on the low fixed point region (that provides a natural explanation
of a large top quark mass) for which we find solutions to the RGE satisfying
both experimental bounds and fine-tuning criteria. We also find that the
constraint from the consideration of the lightest supersymmetric particle as
the dark matter of the universe is accommodated in much of parameter space
where the lightest neutralino is predominantly gaugino. The supersymmetric mass
spectrum displays correlations that are model-independent over much of the GUT
parameter space.Comment: 62 pages + 10 PS figures included (uuencoded), MAD/PH/80
"Large in SU(5)xU(1) supergravity models"
We compute the supersymmetric contribution to the anomalous magnetic moment
of the muon within the context of supergravity models. The
largest possible contributions to occur for the largest allowed
values of and can easily exceed the present experimentally allowed
range, even after the LEP lower bounds on the sparticle masses are imposed.
Such enhancement implies that can greatly exceed
both the electroweak contribution () and the present
hadronic uncertainty (). Therefore, the new E821
Brookhaven experiment (with an expected accuracy of ) should
explore a large fraction (if not all) of the parameter space of these models,
corresponding to slepton, chargino, and squarks masses as high as 200, 300, and
1000 GeV respectively. Moreover, contrary to popular belief, the
contribution can have either sign, depending on the sign of the Higgs mixing
parameter : (). The present
constraint excludes chargino masses in the range 45-120\GeV depending
on the value of , although there are no constraints for
\tan\beta\lsim8. We also compute and find
|a^{susy}_\tau|\approx(m_\tau/m_\mu)^2\,|a^{susy}_\mu|\lsim10^{-5} and
briefly comment on its possible observability.Comment: 10 pages, 4 figures (not included), Latex. Figures available from
[email protected] as ps files (total 0.985MB) or uuencoded file (0.463MB).
CERN-TH.6986/93, CTP-TAMU-44/9
The Mass of the Lightest Supersymmetric Higgs Boson beyond the Leading Logarithm Approximation
We examine the radiative corrections to the mass of the lightest Higgs boson
in the minimal supersymmetric extension of the standard model. We use the
renormalization-group improved effective potential which includes the
next-to-leading-order contributions. We find that, contrary to the result of
Espinosa and Quir\'os, the higher-order corrections to the lightest Higgs boson
mass are non-negligible, adding GeV ( GeV) to the result in the
leading logarithm approximation for the range of top quark mass and for the supersymmetric breaking scale (). Also we find that our result is
stable under the change of the renormalization parameter .Comment: 17 pages (2 figures not included
Very light CP-odd scalar in the Two-Higgs-Doublet Model
We show that a general two-Higgs-doublet model (THDM) with a very light
CP-odd scalar (A) can be compatible with the rho parameter, Br(b --> s\gamma),
R_b, A_b, (g-2) of muon, Br(Upsilon --> A gamma), and the direct search via the
Yukawa process at LEP. For its mass around 0.2 GeV, the muon (g-2) and
Br(Upsilon --> A \gamma) data require tan(beta) to be about 1. Consequently, A
can behave like a fermiophobic CP-odd scalar and predominantly decay into a
photon pair ("gamma gamma"), which registers in detectors of high energy
collider experiments as a single photon signature when the momentum of A is
large. We compute the partial decay width of Z --> A A A and the production
rate of f \bar{f} --> Z A A --> Z +"gamma gamma", f^' {\bar f} --> W^{\pm} A A
--> W^\pm + "gamma gamma" and f \bar f --> H^+ H^- --> W^+ W^- A A --> W^+ W^-
+ "gamma gamma" at high energy colliders such as LEP, Tevatron, LHC, and future
Linear Colliders. Other production mechanisms of a light A, such as gg --> h
--> AA --> "gamma gamma", are also discussed.Comment: Some improvementes, references updated, 3 new figures, one new
appendix, abstract and conclusions unchaged. Version to appear in Physical
Review
Neutralino relic density in a Universe with a non-vanishing cosmological constant
We discuss the relic density of the lightest of the supersymmetric particles
in view of new cosmological data, which favour the concept of an accelerating
Universe with a non-vanishing cosmological constant. Recent astrophysical
observations provide us with very precise values of the relevant cosmological
parameters. Certain of these parameters have direct implications on particle
physics, e.g., the value of matter density, which in conjunction with
electroweak precision data put severe constraints on the supersymmetry breaking
scale. In the context of the Constrained Minimal Supersymmetric Standard Model
(CMSSM) such limits read as: M_{1/2} \simeq 300 \GeV - 340 \GeV, m_0 \simeq
80 \GeV - 130 \GeV. Within the context of the CMSSM a way to avoid these
constraints is either to go to the large and region, or
make , the next to lightest supersymmetric particle (LSP), be
almost degenerate in mass with LSP.Comment: REVTeX, 50 pages, 35 eps figures; Minor changes, references and a
figure added; Better quality figures can be obtained upon request from
[email protected]
Constraints on the Minimal Supergravity Model with Large
In the minimal supergravity model (mSUGRA), as the parameter
increases, the charged Higgs boson and light bottom squark masses decrease,
which can potentially increase contributions from , \tg\tb_j and
\tz_i\tb_j loops in the decay . We update a previous QCD
improved decay calculation to include in addition the effects of
gluino and neutralino loops. We find that in the mSUGRA model, loops involving
charginos also increase, and dominate over , , \tg\tq and
\tz_i\tq contributions for \tan\beta\agt 5-10. We find for large values of
that most of the parameter space of the mSUGRA model for
is ruled out due to too large a value of branching ratio . For and large , most of parameter space is
allowed, although the regions with the least fine-tuning (low and
) are ruled out due to too low a value of . We
compare the constraints from to constraints from the neutralino
relic density, and to expectations for sparticle discovery at LEP2 and the
Fermilab Tevatron colliders. Finally, we show that non-universal GUT
scale soft breaking squark mass terms can enhance gluino loop contributions to
decay rate even if these are diagonal.Comment: 14 page REVTEX file plus 6 PS figure
Effects of Large CP violating phases on g_{\m}-2 in MSSM
Effects of CP violation on the supersymmetric electro-weak correction to the
anomalous magnetic moment of the muon are investigated with the most general
allowed set of CP violating phases in MSSM. The analysis includes contributions
from the chargino and the neutralino exchanges to the muon anomaly. The
supersymmetric contributions depend only on specific combinations of CP phases.
The independent set of such phases is classified. We analyse the effects of the
phases under the EDM constraints and show that large CP violating phases can
drastically affect the magnitude of the supersymmetric electro-weak
contribution to and may even affect its overall sign.Comment: 26 pages Latex file including 4 figure
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