5,846 research outputs found
Cosmological Constants as Messenger between Branes
We present a supersymmetry-breaking scenario in which both the breaking in
the hidden sector with no-scale type supergravity and that in the observable
sector with gauge mediation are taken into account. The breaking scales in the
hidden and observable sectors are related through the vanishing condition of
the cosmological constant with a brane-world picture in mind. Suppressing
flavor-changing neutral currents, we can naturally obtain the gravitino,
Higgs(ino), and soft masses of the electroweak scale.Comment: 7 pages, Late
Simple Scheme for Gauge Mediation
We present a simple scheme for constructing models that achieve successful
gauge mediation of supersymmetry breaking. In addition to our previous work [1]
that proposed drastically simplified models using metastable vacua of
supersymmetry breaking in vector-like theories, we show there are many other
successful models using various types of supersymmetry breaking mechanisms that
rely on enhanced low-energy U(1)_R symmetries. In models where supersymmetry is
broken by elementary singlets, one needs to assume U(1)_R violating effects are
accidentally small, while in models where composite fields break supersymmetry,
emergence of approximate low-energy U(1)_R symmetries can be understood simply
on dimensional grounds. Even though the scheme still requires somewhat small
parameters to sufficiently suppress gravity mediation, we discuss their
possible origins due to dimensional transmutation. The scheme accommodates a
wide range of the gravitino mass to avoid cosmological problems.Comment: 13 page
Dependence of the intrinsic spin Hall effect on spin-orbit interaction character
We report on a comparative numerical study of the spin Hall conductivity in
two-dimensions for three different spin-orbit interaction models; the standard
k-linear Rashba model, the k-cubic Rashba model that describes two-dimensional
hole systems, and a modified k-linear Rashba model in which the spin-orbit
coupling strength is energy dependent. Numerical finite-size Kubo formula
results indicate that the spin Hall conductivity of the k-linear Rashba model
vanishes for frequency much smaller than the scattering rate
, with order one relative fluctuations surviving out to large system
sizes. For the k-cubic Rashba model case, the spin Hall conductivity does not
depend noticeably on and is finite in the {\em dc} limit, in
agreement with experiment. For the modified k-linear Rashba model the spin Hall
conductivity is noticeably dependent but approaches a finite
value in the {\em dc} limit. We discuss these results in the light of a
spectral decomposition of the spin Hall conductivity and associated sum rules,
and in relation to a proposed separation of the spin Hall conductivity into
skew-scattering, intrinsic, and interband vertex correction contributions.Comment: 10 pages, 4 figure
The Spin-SAF transition in NaV2O5 induced by spin-pseudospin coupling
We present microscopic estimates for the spin-spin and spin-speudospin
interactions of the quarter-filled ladder compound NaV2O5, obtained by exactly
diagonalizing appropriate clusters of the underlying generalized Hubbard
Hamiltonian. We present evidence for a substantial interladder spin-pseudospin
interaction term which would allow simultaneously for the
superantiferroelectric (SAF) charge (pseudospin) ordering and spin
dimerization. We discuss the values of the coupling constants appropriate for
NaV2O5 and deduce the absence of a soft antiferroelectric mode
Anisotropic phonon DOS: the application of Rietveld and Mossbauer texture analysis in aligned powders
While synthesizing the single crystals of novel materials is not always
feasible, orienting the layered polycrystals becomes an attractive method in
the studies of angular dependencies of inelastic scattering of x-rays or
neutrons. Putting in use the Rietveld analysis of layered structures in novel
manganites and cuprates we develop the studies of their anisotropic properties
with oriented powders instead of single crystals. Densities of phonon states
(DOS) and atomic thermal displacememts (ATD) are anisotropic in the A-site
ordered manganites LnBaMn2Oy of both y=5 and y=6 series (Ln=Y, La, Sm, Gd). We
establish the angular dependence of DOS on textures of arbitrary strengths,
link the textures observed by x-ray and gamma-ray techniques, and solve the
problem of disentanglement of Goldanskii-Karyagin effect (GKE) and texture in
Moessbauer spectra.Comment: 6 pages; 5 figures, revise
Onset of incommensurability in quantum spin chains
In quantum spin chains, it has been observed that the incommensurability
occurs near valence-bond-solid (VBS)-type solvable points, and the correlation
length becomes shortest at VBS-type points. Besides, the correlation function
decays purely exponentially at VBS-type points, in contrast with the
two-dimensional (2D) Ornstein-Zernicke type behavior in the other region with
an excitation gap. We propose a mechanism to explain the onset of the
incommensurability and the shortest correlation length at VBS-like points. This
theory can be applicable for more general cases.Comment: 9 pages, 2 figure
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