2,056 research outputs found
Probing lepton flavour violation in slepton NLSP scenarios
In supersymmetric models where the gravitino is the lightest superparticle,
the next-to-lightest superparticle (NLSP) is long-lived, and hence could be
collected and studied in detail. We study the prospects of direct detection of
lepton flavour violation in charged slepton NLSP decays. Mixing angles in the
slepton sector as small as ~ 3\times 10^{-2} (9\times 10^{-3}) could be probed
at the 90% confidence level if 3\times 10^3 (3\times 10^4) sleptons could be
collected.Comment: 20 pages, 8 figures. v2:Comments and references are adde
Perspectives for the detection and measurement of Supersymmetry in the focus point region of mSUGRA models with the ATLAS detector at LHC
This paper discusses the ATLAS potential to study Supersymmetry for the
"Focus-Point" region of the parameter space of mSUGRA models. The potential to
discovery a deviation from Standard Model expectations with the first few
of LHC data was studied using the parametrized simulation of the
ATLAS detector. Several signatures were considered, involving hard jets, large
missing energy, and either -tagged jets, opposite-sign isolated electron or
muon pairs, or top quarks reconstructed exploiting their fully hadronic decays.
With only 1 of data each of these signatures may allow to observe
an excess of events over Standard Model expectation with a statistical
significance exceeding 5 standard deviations. An analytical expression was
derived for the shape of the distribution of the dilepton invariant mass
arising from the three-body leptonic decay of the neutralinos under the
hypothesis of heavy scalars, which is appropriate for the focus-point scenario.
The resulting function was used to fit the distribution of the dilepton
invariant mass obtained with simulated LHC data, and to extract the value of
two kinematic endpoints measuring the and
the mass differences. This information was
used to constrain the MSSM parameter space compatible with the data
Selectron Studies at e-e- and e+e- Colliders
Selectrons may be studied in both e-e- and e+e- collisions at future linear
colliders. Relative to e+e-, the e-e- mode benefits from negligible backgrounds
and \beta threshold behavior for identical selectron pair production, but
suffers from luminosity degradation and increased initial state radiation and
beamstrahlung. We include all of these effects and compare the potential for
selectron mass measurements in the two modes. The virtues of the e-e- collider
far outweigh its disadvantages. In particular, the selectron mass may be
measured to 100 MeV with a total integrated luminosity of 1 fb^-1, while more
than 100 fb^-1 is required in e+e- collisions for similar precision.Comment: 16 pages, 11 figure
Anomaly-Mediated Supersymmetry Breaking with Axion
We construct hadronic axion models in the framework of the anomaly-mediated
supersymmetry breaking scenario. If the Peccei-Quinn symmetry breaking is
related to the supersymmetry breaking, mass spectrum of the minimal
anomaly-mediated scenario is modified, which may solve the negative slepton
mass problem in the minimal anomaly-mediated model. We find several classes of
phenomenologically viable models of axion within the framework of the anomaly
mediation and, in particular, we point out a new mechanism of stabilizing the
axion potential. In this class of models, the Peccei-Quinn scale is related to
the messenger scale. We also study phenomenological aspects of this class of
models. We will see that, in some case, the lightest particle among the
superpartners of the standard-model particles is stau while the lightest
superparticle becomes the axino, the superpartner of the axion. With such a
unique mass spectrum, conventional studies of the collider physics and
cosmology for supersymmetric models should be altered.Comment: 20 pages, 5 figures, added footnotes and references for section
Can multi-TeV (top and other) squarks be natural in gauge mediation?
We investigate whether multi-TeV (1-3 TeV) squarks can be natural in models
of gauge mediated SUSY breaking. The idea is that for some boundary condition
of the scalar (Higgs and stop) masses, the Higgs (mass), evaluated at the
renormalization scale GeV, is not very sensitive to (boundary
values of) the scalar masses (this has been called ``focussing'' in recent
literature). Then, the stop masses can be multi-TeV without leading to
fine-tuning in electroweak symmetry breaking. {\em Minimal} gauge mediation
does {\em not} lead to this focussing (for all values of and the
messenger scale): the (boundary value of) the Higgs mass is too small compared
to the stop masses. Also, in minimal gauge mediation, the gaugino masses are of
the same order as the scalar masses so that multi-TeV scalars implies multi-TeV
gauginos (especially gluino) leading to fine-tuning. We discuss ideas to {\em
increase} the Higgs mass relative to the stop masses (so that focussing can be
achieved) and also to {\em suppress} gaugino masses relative to scalar masses
(or to modify the gaugino mass relations) in {\em non-minimal} models of gauge
mediation -- then multi-TeV (top and other) squarks can be natural. Specific
models of gauge mediation which incorporate these ideas and thus have squarks
(and in some cases, the gluino) heavier than a TeV without resulting in
fine-tuning are also studied and their collider signals are contrasted with
those of other models which have multi-TeV squarks.Comment: LaTeX, 29 pages, 9 eps figures. Replacing an earlier version. In
version 3, some references and a minor comment have been added and typos have
been correcte
Mass Determination Method for the Right and Left Selectron Above Production Threshold
The determination of the masses of Supersymmetric particles such as the
Selectron for energies above threshold using the energy end-points method is
subject to signal deconvolution difficulties and to Standard Model and
Supersymmetric backgrounds. The important features of Right and Left Selectron
production are used to design an experimentally robust method both for
determining the Left and Right Selectron masses, the Neutralino mass and for
suppresing backgrounds. The mass resolution is an order of magnitude better
than in previous methods. Additional features, such as the determination of the
relative leptonic branching ratios of the selectron decay are present in the
method.Comment: 4 pages in RevTex (Latex) format and 4 figures in eps forma
Higher-dimensional perturbations of the vacuum energy density
The vacuum energy density arising from the broken supersymmetry of the
(standard-model) fields living on a brane cannot be fully "off-loaded" to the
bulk: even assuming the existence of an effective "self-tuning" mechanism, a
small fraction of the transferred energy "bunces back" to the brane, as a
backreaction of the supersymmetry breaking gravitationally transmitted to the
bulk. In that case the SUSY scale of the brane has to be bounded, to guarantee
the consistency of such a residual energy density with current large-scale
phenomonological constraints. This effect is illustrated by computing the
zero-point energies of the tower of (higher-dimensional) massive states
associated to tensor metric fluctuations on a brane embedded in a warped bulk
geometry, and it is shown to be independent of the number of compact or
non-compact extra dimensions.Comment: 10 pages, no figures, to appear in JHE
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
Flavor and LHC Searches for New Physics
Uncovering the physics of electroweak symmetry breaking (EWSB) is the
raison-d'etre of the LHC. Flavor questions, it would seem, are of minor
relevance for this quest, apart from their role in constraining the possible
structure of EWSB physics. In this short review article, we outline, using
flavor-dependent sleptons as an example, how flavor can affect both searches
for supersymmetry, and future measurements aimed at understanding the nature of
any new discoveries. If the production cross-sections for supersymmetry are
relatively low, as indicated by the fact that it has not revealed itself yet in
standard searches, the usual assumptions about the superpartner spectra need
re-thinking. Furthermore, one must consider more intricate searches, such as
lepton-based searches, which could be susceptible to flavor effects. We start
by reviewing the flavor structure of existing frameworks for mediating
supersymmetry breaking, emphasizing flavor-dependent models proposed recently.
We use the kinematic endpoints of invariant mass distributions to demonstrate
how flavor dependence can impact both searches for supersymmetry and the
Inverse Problem. We also discuss methods for measuring small-mass splittings
and mixings at the LHC, both in models with a neutralino LSP and in models with
a charged slepton (N)LSP.Comment: 11 pages, 1 figure. Invited Review for EPJ
Lepton Flavor Violation at LEP II and Beyond
If sleptons are produced at LEP II or the Next Linear Collider, lepton flavor
violation can be probed at a level significantly below the current bounds from
rare processes, such as . Polarizable beams and the
mode at the NLC are found to be powerful options.Comment: 8 pages, 2 embedded figures, ReVTeX. Talk given at SUSY-96,
University of Maryland, College Park, 29 May - 1 June 199
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