4,720 research outputs found
Secondary emission conductivity of high purity silica fabric
High purity silica fabrics were proposed for use as a material to control the effects of electrostatic charging of satellites at synchronous altitudes. These materials exhibited very quiet behavior when placed in simulated charging environments as opposed to other dielectrics used for passive thermal control which exhibit varying degrees of electrical arcing. Secondary emission conductivity is proposed as a mechanism for this superior behavior. Design of experiments to measure this phenomena and data taken on silica fabrics are discussed as they relate to electrostatic discharge (ESD) control on geosynchronous orbit spacecraft. Studies include the apparent change in resistivity of the material as a function of the electron beam energy, flux intensity, and the effect of varying electric fields impressed across the material under test
micrOMEGAs : a tool for dark matter studies
micrOMEGAs is a tool for cold dark matter (DM) studies in generic extensions
of the standard model with a R-parity like discrete symmetry that guarantees
the stability of the lightest odd particle. The code computes the DM relic
density, the elastic scattering cross sections of DM on nuclei relevant for
direct detection, and the spectra of positrons, anti-protons and photons
originating from DM annihilation including porpagation of charged cosmic rays.
The cross sections and decay properties of new particles relevant for collider
studies are included as well as constraints from the flavour sector on the
parameter space of supersymmetric models.Comment: 10 pages, Proceedings of LC09, e+e- Physics at the TeV scale and the
Dark Matter connection, Perugia, Italy, 21-24 sept. 200
Precision measurements, dark matter direct detection and LHC Higgs searches in a constrained NMSSM
We reexamine the constrained version of the Next-to-Minimal Supersymmetric
Standard Model with semi universal parameters at the GUT scale (CNMSSM). We
include constraints from collider searches for Higgs and SUSY particles, upper
bound on the relic density of dark matter, measurements of the muon anomalous
magnetic moment and of B-physics observables as well as direct searches for
dark matter. We then study the prospects for direct detection of dark matter in
large scale detectors and comment on the prospects for discovery of heavy Higgs
states at the LHC.Comment: 22 pages, 8 figures. Note added and references adde
micrOMEGAs: Version 1.3
We present the latest version of micromegas, a code that calculates the relic
density of the lightest supersymmetric particle in the MSSM. All tree-level
processes for the annihilation of the LSP are included as well as all possible
coannihilation processes with neutralinos, charginos, sleptons, squarks and
gluinos. The cross-sections extracted from CalcHEP are calculated exactly using
loop-corrected masses and mixings as specified in the SUSY Les Houches Accord.
Relativistic formulae for the thermal average are used and care is taken to
handle poles and thresholds by adopting specific integration routines. The
input parameters can be either the soft SUSY parameters in a general MSSM or
the parameters of a SUGRA model specified at some high scale (GUT). In the
latter case, a link with Suspect, Softsusy, Spheno and Isajet allows to
calculate the supersymmetric spectrum, Higgs masses, as well as mixing
matrices. Higher-order corrections to Higgs couplings to quark pairs including
QCD as well as some SUSY corrections (deltaMb) are implemented. Routines
calculating (g-2), bsgamma and bsmumu are also included. In particular the
bsgamma routine includes an improved NLO for the SM and the charged Higgs while
the SUSY large tan(beta) effects beyond leading-order are included. This new
version also provides cross-sections for any 2->2 process as well as partial
decay widths for two-body final states in the MSSM allowing for easy simulation
at colliders.Comment: 45 page
micrOMEGAs4.1: two dark matter candidates
micrOMEGAs is a code to compute dark matter observables in generic extensions
of the standard model. This version of micrOMEGAs includes a generalization of
the Boltzmann equations to take into account the possibility of two dark matter
candidates. The modification of the relic density calculation to include
interactions between the two DM sectors as well as semi-annihilation is
presented. Both DM signals in direct and indirect detection are computed as
well. An extension of the standard model with two scalar doublets and a singlet
is used as an example.Comment: 13 pages, 1 figur
micrOMEGAs: recent developments
The program micrOMEGAs that calculates the relic density of the lightest
supersymmetric particle (LSP) in the MSSM is presented. The impact of
coannihilation channels and of higher order corrections to Higgs widths is
stressed. The dependence on the RGE code used to calculate the soft parameters
is also discussed.Comment: 5 pages, 2 figures, Talk presented at IDM2002, York, England;
Reference adde
Isospin-violating dark matter from a double portal
We study a simple model that can give rise to isospin-violating interactions
of Dirac fermion asymmetric dark matter to protons and neutrons through the
interference of a scalar and U(1) gauge boson contribution. The model can
yield a large suppression of the elastic scattering cross section off Xenon
relative to Silicon thus reconciling CDMS-Si and LUX results while being
compatible with LHC findings on the 126 GeV Higgs, electroweak precision tests
and flavour constraints.Comment: 25 pages, 7 figure
Relic density of dark matter in mSUGRA and non-universal SUGRA
The measurements of WMAP on the relic density of dark matter strongly
constrain supersymmetric models. In mSUGRA where the neutralino LSP is mostly a
bino only rather fine-tuned models survive. On the other hand the relic density
upper limit can be easily satisfied in models with a Higgsino or wino LSP.Comment: 8 pages, 3 figures, Invited talk at Physics at LHC, Vienna, July 200
The top squark-mediated annihilation scenario and direct detection of dark matter in compressed supersymmetry
Top squark-mediated annihilation of bino-like neutralinos to top-antitop
pairs can play the dominant role in obtaining a thermal relic dark matter
abundance in agreement with observations. In a previous paper, it was argued
that this can occur naturally in models of compressed supersymmetry, which
feature a running gluino mass parameter that is substantially smaller than the
wino mass parameter at the scale of apparent gauge coupling unification. Here I
study in some more detail the parameter space in which this is viable, and
compare to other scenarios for obtaining the observed dark matter density. I
then study the possibility of detecting the dark matter directly in future
experiments. The prospects are consistently very promising for a wide variety
of model parameters within this scenario.Comment: 17 pages. v2: additions to figures 4 and
Natural regulatory (CD4+CD25+FOXP+) T cells control the production of pro-inflammatory cytokines during Plasmodium chabaudi adami infection and do not contribute to immune evasion.
Different functions have been attributed to natural regulatory CD4+CD25+FOXP+ (Treg) cells during malaria infection. Herein, we assessed the role for Treg cells during infections with lethal (DS) and non-lethal (DK) Plasmodium chabaudi adami parasites, comparing the levels of parasitemia, inflammation and anaemia. Independent of parasite virulence, the population of splenic Treg cells expanded during infection, and the absolute numbers of activated CD69+ Treg cells were higher in DS-infected mice. In vivo depletion of CD25+ T cells, which eliminated 80% of CD4+FOXP3+CD25+ T cells and 60–70% of CD4+FOXP3+ T cells, significantly decreased the number of CD69+ Treg cells in mice with lethal malaria. As a result, higher parasite burden and morbidity were measured in the latter, whereas the kinetics of infection with non-lethal parasites remained unaffected. In the absence of Treg cells, parasite-specific IFN-γ responses by CD4+ T cells increased significantly, both in mice with lethal and non-lethal infections, whereas IL-2 production was only stimulated in mice with non-lethal malaria. Following the depletion of CD25+ T cells, the production of IL-10 by CD90− cells was also enhanced in infected mice. Interestingly, a potent induction of TNF- and IFN-γ production by CD4+ and CD90− lymphocytes was measured in DS-infected mice, which also suffered severe anaemia earlier than non-depleted infected controls. Taken together, our data suggest that the expansion and activation of natural Treg cells represent a counter-regulatory response to the overwhelming inflammation associated with lethal P.c. adami. This response to infection involves TH1 lymphocytes as well as cells from the innate immune system
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