3,317 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
Light mixed sneutrinos as thermal dark matter
In supersymmetric models with Dirac neutrino masses, a left-right mixed
sneutrino can be a viable dark matter candidate. We examine the
MSSM+ parameter space where this is the case with particular
emphasis on light sneutrinos with masses below 10 GeV. We discuss implications
for direct and indirect dark matter searches, including the relevant
uncertainties, as well as consequences for collider phenomenology.Comment: 33 pages, 14 figures; one figure and references adde
Equilibrium random-field Ising critical scattering in the antiferromagnet Fe(0.93)Zn(0.07)F2
It has long been believed that equilibrium random-field Ising model (RFIM)
critical scattering studies are not feasible in dilute antiferromagnets close
to and below Tc(H) because of severe non-equilibrium effects. The high magnetic
concentration Ising antiferromagnet Fe(0.93)Zn(0.07)F2, however, does provide
equilibrium behavior. We have employed scaling techniques to extract the
universal equilibrium scattering line shape, critical exponents nu = 0.87 +-
0.07 and eta = 0.20 +- 0.05, and amplitude ratios of this RFIM system.Comment: 4 pages, 1 figure, minor revision
How light can the lightest neutralino be?
In this talk we summarize previous work on mass bounds of a light neutralino
in the Minimal Supersymmetric Standard Model. We show that without the GUT
relation between the gaugino mass parameters M_1 and M_2, the mass of the
lightest neutralino is essentially unconstrained by collider bounds and
precision observables. We conclude by considering also the astrophysics and
cosmology of a light neutralino.Comment: 6 pages, 3 figures, to appear in the proceedings of the 16th
International Symposium on Particles, Strings and Cosmology (PASCOS2010),
Valencia (Spain), July 19th - 23rd, 201
Relic density of neutralino dark matter in the MSSM with CP violation
We calculate the relic density of dark matter in the MSSM with CP violation.
We analyse various scenarios of neutralino annihilation: the cases of a bino,
bino-wino and bino-Higgsino LSP, annihilation through Higgs, as well as
sfermion coannihilation scenarios. Large phase effects are found, on the one
hand due to shifts in the masses, on the other hand due to modifications of the
couplings. Taking special care to disentangle the effects in masses and
couplings, we demonstrate that the presence of CP phases can have a significant
influence on the neutralino relic abundance. Typical variations in \Omega h^2
solely from modifications in the couplings are O(10%-100%), but can reach an
order of magnitude in some cases.Comment: 36 pages, 21 figures (low resolution). A version with high-resolution
figures can be downloaded from http://cern.ch/kraml/papers/omc
Fast vectorized algorithm for the Monte Carlo Simulation of the Random Field Ising Model
An algoritm for the simulation of the 3--dimensional random field Ising model
with a binary distribution of the random fields is presented. It uses
multi-spin coding and simulates 64 physically different systems simultaneously.
On one processor of a Cray YMP it reaches a speed of 184 Million spin updates
per second. For smaller field strength we present a version of the algorithm
that can perform 242 Million spin updates per second on the same machine.Comment: 13 pp., HLRZ 53/9
Weak first order transition in the three-dimensional site-diluted Ising antiferromagnet in a magnetic field
We perform intensive numerical simulations of the three-dimensional
site-diluted Ising antiferromagnet in a magnetic field at high values of the
external applied field. Even if data for small lattice sizes are compatible
with second-order criticality, the critical behavior of the system shows a
crossover from second-order to first-order behavior for large system sizes,
where signals of latent heat appear. We propose "apparent" critical exponents
for the dependence of some observables with the lattice size for a generic
(disordered) first-order phase transition.Comment: Final version, accepted for publicatio
Glassy transition in the three-dimensional random field Ising model
The high temperature phase of the three dimensional random field Ising model
is studied using replica symmetry breaking framework. It is found that, above
the ferromagnetic transition temperature T_f, there appears a glassy phase at
intermediate temperatures T_f<T<T_b while the usual paramagnetic phase exists
for T>T_b only. Correlation length at T_b is computed and found to be
compatible with previous numerical results.Comment: 7 pages, LaTeX file, preprint 1014 - Rome
Specific-Heat Exponent of Random-Field Systems via Ground-State Calculations
Exact ground states of three-dimensional random field Ising magnets (RFIM)
with Gaussian distribution of the disorder are calculated using
graph-theoretical algorithms. Systems for different strengths h of the random
fields and sizes up to N=96^3 are considered. By numerically differentiating
the bond-energy with respect to h a specific-heat like quantity is obtained,
which does not appear to diverge at the critical point but rather exhibits a
cusp. We also consider the effect of a small uniform magnetic field, which
allows us to calculate the T=0 susceptibility. From a finite-size scaling
analysis, we obtain the critical exponents \nu=1.32(7), \alpha=-0.63(7),
\eta=0.50(3) and find that the critical strength of the random field is
h_c=2.28(1). We discuss the significance of the result that \alpha appears to
be strongly negative.Comment: 9 pages, 9 figures, 1 table, revtex revised version, slightly
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