4,066 research outputs found
Effects of SO(10) D-Terms on SUSY Signals at the Tevatron
We study signals for the production of superparticles at the Tevatron in
supergravity scenarios based on the Grand Unified group SO(10). The breaking of
this group introduces extra contributions to the masses of all scalars,
described by a single new parameter. We find that varying this parameter can
considerably change the size of various expected signals studied in the
literature, with different numbers of jets and/or charged leptons in the final
state. The ratios of these signal can thus serve as a diagnostic to detect or
constrain deviations from the much--studied scenario where all scalar masses
are universal at the GUT scale. Moreover, under favorable circumstances some of
these signals, and/or new signals involving hard jets, should be observable
at the next run of the Tevatron collider even if the average scalar mass lies
well above the gluino mass.Comment: 17 pages, LaTeX including 3 postscript figures, uses equation.st
Hour-glass magnetic spectrum in a stripe-less insulating transition metal oxide
An hour-glass shaped magnetic excitation spectrum appears to be an universal
characteristic of the high-temperature superconducting cuprates. Fluctuating
charge stripes or alternative band structure approaches are able to explain the
origin of these spectra. Recently, an hour- glass spectrum has been observed in
an insulating cobaltate, thus, favouring the charge stripe scenario. Here we
show that neither charge stripes nor band structure effects are responsible for
the hour-glass dispersion in a cobaltate within the checkerboard charge ordered
regime of La2-xSrxCoO4. The search for charge stripe ordering reflections
yields no evidence for charge stripes in La1.6Sr0.4CoO4 which is supported by
our phonon studies. With the observation of an hour-glass-shaped excitation
spectrum in this stripe-less insulating cobaltate, we provide experimental
evidence that the hour-glass spectrum is neither necessarily connected to
charge stripes nor to band structure effects, but instead, probably intimately
coupled to frustration and arising chiral or non-collinear magnetic
correlations
Open charm contribution to dilepton spectra produced in nuclear collisions at SPS energies
Measurements of open charm hadro-production from CERN and Fermilab
experiments are reviewed, with particular emphasis on the absolute cross
sections and on their A and sqrt(s) dependences. Differential pt and xf cross
sections calculated with the Pythia event generator are found to be in
reasonable agreement with recent data. The calculations are scaled to
nucleus-nucleus collisions and the expected lepton pair yield is deduced. The
charm contribution to the low mass dilepton continuum observed by the CERES
experiment is found to be negligible. In particular, it is shown that the
observed low mass dilepton excess in S-Au collisions cannot be explained by
charm enhancement.Comment: 19 pages, 12 eps figures included. To be published in Z.Phys.
Processes at High Energy pp Colliders
In this note we investigate the production of charged heavy particles via
\gaga\ fusion at high energy pp colliders. We revise previous claims that the
\gaga\ cross section is comparable to or larger than that for the corresponding
Drell-Yan process at high energies. Indeed we find that the \gaga\ contribution
to the total production cross section at pp is far below the Drell-Yan cross
section. As far as the individual elastic, semi-elastic and inelastic
contributions to the \gaga\ process are concerned we find that they are all of
the same order of magnitude.Comment: REVTEX, 12 pages, two uuencoded figures appended at the end of the
fil
Determining the Mass of Dark Matter Particles with Direct Detection Experiments
In this article I review two data analysis methods for determining the mass
(and eventually the spin-independent cross section on nucleons) of Weakly
Interacting Massive Particles with positive signals from direct Dark Matter
detection experiments: a maximum likelihood analysis with only one experiment
and a model-independent method requiring at least two experiments.
Uncertainties and caveats of these methods will also be discussed.Comment: 24 pages, 10 figures, 1 reference added, typos fixed, published
version, to appear in the NJP Focus Issue on "Dark Matter and Particle
Physics
Looking for a heavy wino LSP in collider and dark matter experiments
We investigate the phenomenology of a wino LSP as obtained in AMSB and some
string models. The WMAP constraint on the DM relic density implies a wino LSP
mass of 2.0-2.3 TeV. We find a viable signature for such a heavy wino at CLIC,
operating at its highest CM energy of 5 TeV. One also expects a viable
monochromatic -ray signal from its pair-annihilation at the galactic
centre at least for cuspy DM halo profiles.Comment: A discussion on non-perturbative effects on annihilation cross
section of TeV scale wino LSP added. Version to appear in Phys. Rev. D
Higgs funnel region of SUSY dark matter for small and renormalization group effects on pseudoscalar Higgs boson with scalar mass non-universality
A non-universal scalar mass supergravity type of model is explored where the
first two generation of scalars and the third generation of sleptons may be
very massive. Lighter or vanishing third generation of squarks as well as Higgs
scalars at the unification scale cause the radiative electroweak symmetry
breaking constraint to be less prohibitive. Thus, both FCNC/CP-violation
problems as well as the naturalness problem are within control. We identify a
large slepton mass effect in the RGE of (for the down type of
Higgs) that may turn the later negative at the electroweak scale even for a
small . A hyperbolic branch/focus point like effect is found for
that may result in very light Higgs spectra. The lightest stable
particle is dominantly a bino that pair annihilates via Higgs exchange, giving
rise to a WMAP satisfied relic density region for all . Detection
prospects of such LSPs in the upcoming dark matter experiments both of direct
and indirect types (photon flux) are interesting. The Higgs bosons and the
third generation of squarks are light in this scenario and these may be easily
probed besides charginos and neutralinos in the early runs of LHC.Comment: 36 pages and 7 Postscript files. Minor changes in the text. Version
accepted for publication in Phys. Rev.
Light Stop Searches at the LHC in Events with two b-Jets and Missing Energy
We propose a new method to discover light top squarks (stops) in the
co-annihilation region at the Large Hadron Collider (LHC). The bino-like
neutralino is the lightest supersymmetric particle (LSP) and the lighter stop
is the next-to-LSP. Such scenarios can be consistent with electroweak
baryogenesis and also with dark matter constraints. We consider the production
of two stops in association with two b-quarks, including pure QCD as well as
mixed electroweak-QCD contributions. The stops decay into a charm quark and the
LSP. For a higgsino-like light chargino the electroweak contributions can
exceed the pure QCD prediction. We show the size of the electroweak
contributions as a function of the stop mass and present the LHC discovery
reach in the stop-neutralino mass plane.Comment: 12 pages, 10 figure
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