490 research outputs found
Scalar Dark Matter From Theory Space
The scalar dark matter candidate in a prototypical theory space little Higgs
model is investigated. We review all details of the model pertinent to dark
matter. We perform a thermal relic density calculation including couplings to
the gauge and Higgs sectors of the model. We find two regions of parameter
space that give acceptable dark matter abundances. The first region has a dark
matter candidate with a mass of order 100 GeV, the second region has a heavy
candidate with a mass greater than about 500 GeV$. The dark matter candidate in
either region is an admixture of an SU(2) triplet and an SU(2) singlet, thereby
constituting a WIMP (weakly interacting massive particle).Comment: 18 pages, 2 figures, version to appear in PR
Phenomenological Aspects of Heterotic Orbifold Models at One Loop
We provide a detailed study of the phenomenology of orbifold
compactifications of the heterotic string within the context of supergravity
effective theories. Our investigation focuses on those models where the soft
Lagrangian is dominated by loop contributions to the various soft supersymmetry
breaking parameters. Such models typically predict non-universal soft masses
and are thus significantly different from minimal supergravity and other
universal models. We consider the pattern of masses that are governed by these
soft terms and investigate the implications of certain indirect constraints on
supersymmetric models, such as flavor-changing neutral currents, the anomalous
magnetic moment of the muon and the density of thermal relic neutralinos. These
string-motivated models show novel behavior that interpolates between the
phenomenology of unified supergravity models and models dominated by the
superconformal anomaly.Comment: 47 pages, 14 figure
Higgsino Dark Matter in a SUGRA Model with Nonuniversal Gaugino Masses
We study a specific SUGRA model with nonuniversal gaugino masses as an
alternative to the minimal SUGRA model in the context of supersymmetric dark
matter. The lightest supersymmetric particle in this model comes out to be a
Higgsino dominated instead of a bino dominated lightest neutralino. The thermal
relic density of this Higgsino dark matter is somewhat lower than the
cosmologically favoured range, which means it may be only a subdominant
component of the cold dark matter. Nonetheless, it predicts favourable rates of
indirect detection, which can be seen in square-km size neutrino telescopes.Comment: Version to appear in Phys. Rev. D. A few references added in the
bibliography and a comment added in Section 2. LaTex, 16 pages, 4 figure
The Well-Tempered Neutralino
The dark-matter prediction is usually considered as one of the successes of
low-energy supersymmetry. We argue that, after LEP constraints are taken into
account, the correct prediction for the dark-matter density, at a quantitative
level, is no longer a natural consequence of supersymmetry, but it requires
special relations among parameters, highly sensitive to small variations. This
is analogous to the problem of electroweak-symmetry breaking, where the correct
value of the Z mass is obtained only with a certain degree of fine tuning. In
the general parameter space of low-energy supersymmetry, one of the most
plausible solution to reproduce the correct value of the dark-matter density is
the well-tempered neutralino, which corresponds to the boundary between a pure
Bino and a pure Higgsino or Wino. We study the properties of well-tempered
neutralinos and we propose a simple limit of split supersymmetry that realizes
this situation.Comment: Latex2e, 29 pages, 5 figures, reference added, typo corrected,
version to be published in NP
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
Nickel oxide reduction studied by environmental TEM and in situ XRD
Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 - August 2, 201
Dynamic study of carbon nanotube growth and catalyst morphology evolution during acetylene decomposition on Co/SBA-15 in an environmental TEM
International @ SURFACES+FCA:MAO:ATUInternational audienceNon
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