177 research outputs found
Bi-maximal mixing at GUT, the low energy data and the leptogenesis
In the framework of the minimum supersymmetric model with right-handed
neutrinos, we consider the Bi-maximal mixing which is realized at the GUT scale
and discuss a question that this model can reproduce the low energy phenomena
and the leptogenesis.Comment: Talk given by E. Takasugi at NuFact04, Osaka, Japan, July 26 - August
1,2004 - 3 pages, 4 figure
Disorder-Induced Multiple Transition involving Z2 Topological Insulator
Effects of disorder on two-dimensional Z2 topological insulator are studied
numerically by the transfer matrix method. Based on the scaling analysis, the
phase diagram is derived for a model of HgTe quantum well as a function of
disorder strength and magnitude of the energy gap. In the presence of sz
non-conserving spin-orbit coupling, a finite metallic region is found that
partitions the two topologically distinct insulating phases. As disorder
increases, a narrow-gap topologically trivial insulator undergoes a series of
transitions; first to metal, second to topological insulator, third to metal,
and finally back to trivial insulator. We show that this multiple transition is
a consequence of two disorder effects; renormalization of the band gap, and
Anderson localization. The metallic region found in the scaling analysis
corresponds roughly to the region of finite density of states at the Fermi
level evaluated in the self-consistent Born approximation.Comment: 5 pages, 5 figure
Anomalous Hall effect in ferromagnetic semiconductors
We present a theory of the anomalous Hall effect in ferromagnetic (Mn,III)V
semiconductors. Our theory relates the anomalous Hall conductance of a
homogeneous ferromagnet to the Berry phase acquired by a quasiparticle
wavefunction upon traversing closed paths on the spin-split Fermi surface of a
ferromagnetic state. It can be applied equally well to any itinerant electron
ferromagnet. The quantitative agreement between our theory and experimental
data in both (In,Mn)As and (Ga,Mn)As systems suggests that this disorder
independent contribution to the anomalous Hall conductivity dominates in
diluted magnetic semiconductors.Comment: 4 pages, 2 figure
Chirality driven anomalous Hall effect in weak coupling regime
Anomalous Hall effect arising from non-trivial spin configuration (chirality)
is studied based on the - model. Considering a weak coupling case, the
interaction is treated perturbatively. Scattering by normal impurities is
included. Chirality is shown to drive locally Hall current and leads to overall
Hall effect if there is a finite uniform chirality. This contribution is
independent of the conventional spin-orbit contribution and shows distinct low
temperature behavior. In mesoscopic spin glasses, chirality-induced anomalous
Hall effect is expected below the spin-glass transition temperature.
Measurement of Hall coefficient would be useful in experimentally confirming
the chirality ordering
Theory of Ferromagnetism in Ca1-xLaxB6
Novel ferromagnetism in CaLaB is studied in terms of the
Ginzburg-Landau theory for excitonic order parameters, taking into account
symmetry of the wavefunctions. We found that the minima of the free energy
break both inversion and time-reversal symmetries, while the product of these
two remains preserved. This explains various novelties of the ferromagnetism
and predicts a number of magnetic properties, including the magnetoelectric
effect, which can be tested experimentally.Comment: 5 pages, accepted for publication in Phys.Rev.Let
Orbital ferromagnetism and anomalous Hall effect in antiferromagnets on distorted fcc lattice
The Berry phase due to the spin wavefunction gives rise to the orbital
ferromagnetism and anomalous Hall effect in the non-coplanar antiferromagnetic
ordered state on face centered cubic (fcc) lattice once the crystal is
distorted perpendicular to (1,1,1) or (1,1,0)- plane. The relevance to the real
systems -FeMn and NiS is also discussed.Comment: 4 pages, 3 figure
Theory of Excitonic States in CaB6
We study the excitonic states in CaB6 in terms of the Ginzburg-Landau theory.
By minimizing the free energy and by comparing with experimental results, we
identify two possible ground states with exciton condensation. They both break
time-reversal and inversion symmetries. This leads to various magnetic and
optical properties. As for magnetic properties, it is expected to be an
antiferromagnet, and its spin structure is predicted. It will exhibit the
magnetoelectric effect, and observed novel ferromagnetism in doped samples and
in thin-film and powder samples can arise from this effect. Interesting optical
phenomena such as the nonreciprocal optical effect and the second harmonic
generation are predicted. Their measurement for CaB6 will clarify whether
exciton condensation occurs or not and which of the two states is realized.Comment: 17 pages, 3 figure
Exploring the neutrino mass matrix at M_R scale
We discuss the neutrino mass matrix which predicts zero or small values of
|V_{13}| in MSSM and found the inequality, sin^2 2theta_{12} <= sin^2
2theta_sol, where sin^2 2theta_{12} is the mixing angle at M_R scale and sin^2
2theta_{sol} is the value determined by the solar neutrino oscillation. This
constraint says that the model which predicts a larger value of tan^2
theta_{sol} at M_R than the experimental value is excluded. In particular, the
bi-maximal mixing scheme at M_R scale is excluded, from the experimental value
tan^2 theta_sol<1. In this model, |V_{13}| and a Dirac phase at m_Z are induced
radiatively and turn out to be not small. The effective neutrino mass is
expected to be of order 0.05 eV.Comment: revtex4, 20 pages, 6 figure
Quantum Spin Pump in S=1/2 antiferromagnetic chains -Holonomy of phase operators in sine-Gordon theory-
In this paper, we propose the quantum spin pumping in quantum spin systems
where an applied electric field () and magnetic field () cause a finite
spin gap to its critical ground state. When these systems are subject to
alternating electromangetic fields; and travel along the {\it{loop}} which encloses
their critical ground state in this - phase diagram, the locking
potential in the sine-Gordon model slides and changes its minimum. As a result,
the phase operator acquires holonomy during one cycle along
, which means that the quantized spin current has been
transported through the bulk systems during this adiabatic process. The
relevance to real systems such as Cu-benzoate and is
also discussed.Comment: 10 pages, 5 figures, to be published in J. Phys. Soc. Jpn. 74 (2005)
no. 4. Typos corrected in the revised versio
Genome-wide Runx2 occupancy in prostate cancer cells suggests a role in regulating secretion
Runx2 is a metastatic transcription factor (TF) increasingly expressed during prostate cancer (PCa) progression. Using PCa cells conditionally expressing Runx2, we previously identified Runx2-regulated genes with known roles in epithelial–mesenchymal transition, invasiveness, angiogenesis, extracellular matrix proteolysis and osteolysis. To map Runx2-occupied regions (R2ORs) in PCa cells, we first analyzed regions predicted to bind Runx2 based on the expression data, and found that recruitment to sites upstream of the KLK2 and CSF2 genes was cyclical over time. Genome-wide ChIP-seq analysis at a time of maximum occupancy at these sites revealed 1603 high-confidence R2ORs, enriched with cognate motifs for RUNX, GATA and ETS TFs. The R2ORs were distributed with little regard to annotated transcription start sites (TSSs), mainly in introns and intergenic regions. Runx2-upregulated genes, however, displayed enrichment for R2ORs within 40 kb of their TSSs. The main annotated functions enriched in 98 Runx2-upregulated genes with nearby R2ORs were related to invasiveness and membrane trafficking/secretion. Indeed, using SDS–PAGE, mass spectrometry and western analyses, we show that Runx2 enhances secretion of several proteins, including fatty acid synthase and metastasis-associated laminins. Thus, combined analysis of Runx2's transcriptome and genomic occupancy in PCa cells lead to defining its novel role in regulating protein secretion
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