5,065 research outputs found
Detection of weak-order phase transitions in ferromagnets by ac resistometry
It is shown that ac resistometry can serve as an effective tool for the
detection of phase transitions, such as spin reorientation or premartensitic
phase transitions, which generally are not disclosed by dc resistivity
measurement. Measurement of temperature dependence of impedance, , allows
one to unmask the anomaly, corresponding to a weak-order phase transition. The
appearance of such an anomaly is accounted for by a change in the effective
permeability of a sample upon the phase transition. Moreover, frequency
dependence of makes it possible to use the frequency of the applied ac
current as an adjusting parameter in order to make this anomaly more
pronounced. The applicability of this method is tested for the rare earth Gd
and Heusler alloy NiMnGa.Comment: 4 pages, 2 figures, to be published in J. Appl. Phys., v.94(5
Neutralino Decays in the Complex MSSM at One-Loop: a Comparison of On-Shell Renormalization Schemes
We evaluate two-body decay modes of neutralinos in the Minimal Supersymmetric
Standard Model with complex parameters (cMSSM). Assuming heavy scalar quarks we
take into account all two-body decay channels involving charginos, neutralinos,
(scalar) leptons, Higgs bosons and Standard Model gauge bosons. The evaluation
of the decay widths is based on a full one-loop calculation including hard and
soft QED radiation. Of particular phenomenological interest are decays
involving the Lightest Supersymmetric Particle (LSP), i.e. the lightest
neutralino, or a neutral or charged Higgs boson. For the chargino/neutralino
sector we employ two different renormalization schemes, which differ in the
treatment of the complex phases. In the numerical analysis we concentrate on
the decay of the heaviest neutralino and show the results in the two different
schemes. The higher-order corrections of the heaviest neutralino decay widths
involving the LSP can easily reach a level of about 10-15%, while the
corrections to the decays to Higgs bosons are up to 20-30%, translating into
corrections of similar size in the respective branching ratios. The difference
between the two schemes, indicating the size of unknown two-loop corrections,
is less than order(0.1%). These corrections are important for the correct
interpretation of LSP and Higgs production at the LHC and at a future linear
e+e- collider. The results will be implemented into the Fortran code FeynHiggs.Comment: 49 pages, 27 figures, typos corrected. arXiv admin note: substantial
text overlap with arXiv:1112.0760, arXiv:1111.7289, arXiv:1204.400
Non-perturbative corrections to mean-field behavior: spherical model on spider-web graph
We consider the spherical model on a spider-web graph. This graph is
effectively infinite-dimensional, similar to the Bethe lattice, but has loops.
We show that these lead to non-trivial corrections to the simple mean-field
behavior. We first determine all normal modes of the coupled springs problem on
this graph, using its large symmetry group. In the thermodynamic limit, the
spectrum is a set of -functions, and all the modes are localized. The
fractional number of modes with frequency less than varies as for tending to zero, where is a constant. For an
unbiased random walk on the vertices of this graph, this implies that the
probability of return to the origin at time varies as ,
for large , where is a constant. For the spherical model, we show that
while the critical exponents take the values expected from the mean-field
theory, the free-energy per site at temperature , near and above the
critical temperature , also has an essential singularity of the type
.Comment: substantially revised, a section adde
Desenvolvimento de um ambiente facilitador de integração de ferramentas de mineração de textos.
O objetivo deste trabalho é criar um ambiente que integre as várias ferramentas desenvolvidas e utilizadas nos projetos Tiena (MOURA et al., 2010) e Ainfo6 (PRAXEDES et al., 2009)
Geomagnetically Trapped Particles and Soft Errors on IC Observed in a Satellite
開始ページ、終了ページ: 冊子体のページ付
Thermally-induced magnetic phases in an Ising spin Kondo lattice model on a kagome lattice at 1/3-filling
Numerical investigation on the thermodynamic properties of an Ising spin
Kondo lattice model on a kagome lattice is reported. By using Monte Carlo
simulation, we investigated the magnetic phases at 1/3-filling. We identified
two successive transitions from high-temperature paramagnetic state to a
Kosterlitz-Thouless-like phase in an intermediate temperature range and to a
partially disordered phase at a lower temperature. The partially disordered
state is characterized by coexistence of antiferromagnetic hexagons and
paramagnetic sites with period . We compare the results
with those for the triangular lattice case.Comment: 4 pages, 2 figure
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