174 research outputs found
Predominant Magnetic States in Hubbard Model on Anisotropic Triangular Lattices
Using an optimization variational Monte Carlo method, we study the
half-filled-band Hubbard model on anisotropic triangular lattices, as a
continuation of the preceding study [J. Phys. Soc. Jpn 75, 074707 (2006)]. We
introduce two new trial states: (i) A coexisting state of
(\pi,\pi)-antiferromagnetic (AF) and a d-wave singlet gaps, in which we allow
for a band renormalization effect, and (ii) a state with an AF order of
120^\circ spin structure. In both states, a first-order metal-to-insulator
transition occurs at smaller U/t than that of the pure d-wave state. In
insulating regimes, magnetic orders always exist; an ordinary (\pi,\pi)-AF
order survives up to t'/t\sim 0.9 (U/t=12), and a 120^\circ-AF order becomes
dominant for t'/t \gsim 0.9. The regimes of the robust superconductor and of
the nonmagnetic insulator the preceding study proposed give way to these
magnetic domains.Comment: 11 pages, 14 figure
Study of hadron interactions in a lead-emulsion target
Topological and kinematical characteristics of hadron interactions have been
studied using a lead-emulsion target exposed to 2, 4 and 10 GeV/c hadron beams.
A total length of 60 m tracks was followed using a high speed automated
emulsion scanning system. A total of 318 hadron interaction vertices and their
secondary charged particle tracks were reconstructed. Measurement results of
interaction lengths, charged particle multiplicity, emission angles and momenta
of secondary charged particles are compared with a Monte Carlo simulation and
appear to be consistent. Nuclear fragments emitted from interaction vertices
were also detected by a newly developed emulsion scanning system with
wide-angle acceptance. Their emission angle distributions are in good agreement
with the simulated distributions. Probabilities of an event being associated
with at least one fragment track are found to be greater than 50% for beam
momentum GeV/c and are well reproduced by the simulation. These
experimental results validate estimation of the background due to hadron
interactions in the sample of decay candidates in the OPERA oscillation experiment.Comment: 14 pages, 11 figure
Momentum reconstruction of charged particles using multiple Coulomb scatterings in a nuclear emulsion detector
This paper describes a new method for momentum reconstruction of charged
particles using multiple Coulomb scatterings (MCS) in a nuclear emulsion
detector with a layered structure of nuclear emulsion films and target
materials. The method utilizes the scattering angles of particles precisely
measured in the emulsion films. The method is based on the maximum likelihood
to newly include information on the decrease of the energy as the particle
travels through the detector. According to the MC simulations, this method can
measure momentum with a resolution of 10% for muons of 500 MeV/c passing
through the detector perpendicularly. The momentum resolution is evaluated to
be 10-20%, depending on the momentum and emission angle of the particle. By
accounting for the effect of the energy decrease, the momentum can be
reconstructed correctly with less bias, particularly in the low-momentum
region. We apply this method to measure the momentum of muon tracks detected in
the NINJA experiment where the momentum is also measured independently by using
the track range. The two measurements agree well within experimental
uncertainties of a 2% difference, verifying the method experimentally. This
method will extend the measurable phase space of muons and hadrons in the NINJA
experiment.Comment: 19 pages, 14 figure
Cluster formation and the Sunyaev-Zel'dovich power spectrum in modified gravity: the case of a phenomenologically extended DGP model
We investigate the effect of modified gravity on cluster abundance and the
Sunyaev-Zel'dovich angular power spectrum. Our modified gravity is based on a
phenomenological extension of the Dvali-Gabadadze-Porrati model which includes
two free parameters characterizing deviation from Lambda-CDM cosmology.
Assuming that Birkhoff's theorem gives a reasonable approximation, we study the
spherical collapse model of structure formation and show that while the growth
function changes to some extent, modified gravity gives rise to no significant
change in the linear density contrast at collapse time. The growth function is
enhanced in the so called normal branch, while in the "self-accelerating"
branch it is suppressed. The Sunyaev-Zel'dovich angular power spectrum is
computed in the normal branch, which turns out to be amplified compared to the
Lambda-CDM case. This allows us to put observational constraints on the
parameters of the modified gravity model using small scale CMB observation
data.Comment: 9 pages, 9 figures, submitted to MNRA
Variational Monte Carlo studies of a t-J model on an anisotropic triangular lattice
With the insulating phase of \kappa-(BEDT-TTF)_2X in mind, we study a t-J
model on an anisotropic triangular lattice, where the hopping integral is t' in
one of the three directions, using a variational Monte Carlo method. By
changing the value of t'/t, we study the stability of superconducting (SC)
states with d- and d+id-wave symmetries and of an antiferromagnetic (AF) state.
As t'/t decreases from 1, the stable state immediately switches from the d+id
wave to the d wave. The AF state is stabilized from the normal spin liquid
state for t'/t\lsim 0.7 at half filling. We also take account of Nagaoka
ferromagnetism and a phase separation.Comment: 4 pages, 3 figure
The double-stranded break-forming activity of plant SPO11s and a novel rice SPO11 revealed by a Drosophila bioassay
<p>Abstract</p> <p>Background</p> <p>SPO11 is a key protein for promoting meiotic recombination, by generating chromatin locus- and timing-specific DNA double-strand breaks (DSBs). The DSB activity of SPO11 was shown by genetic analyses, but whether SPO11 exerts DSB-forming activity by itself is still an unanswered question. DSB formation by SPO11 has not been detected by biochemical means, probably because of a lack of proper protein-folding, posttranslational modifications, and/or specific SPO11-interacting proteins required for this activity. In addition, plants have multiple SPO11-homologues.</p> <p>Results</p> <p>To determine whether SPO11 can cleave DNA by itself, and to identify which plant SPO11 homologue cleaves DNA, we developed a <it>Drosophila </it>bioassay system that detects the DSB signals generated by a plant SPO11 homologue expressed ectopically. We cytologically and genetically demonstrated the DSB activities of <it>Arabidopsis </it>AtSPO11-1 and AtSPO11-2, which are required for meiosis, in the absence of other plant proteins. Using this bioassay, we further found that a novel SPO11-homologue, OsSPO11D, which has no counterpart in <it>Arabidopsis</it>, displays prominent DSB-forming activity. Quantitative analyses of the rice SPO11 transcripts revealed the specific increase in OsSPO11D mRNA in the anthers containing meiotic pollen mother cells.</p> <p>Conclusions</p> <p>The <it>Drosophila </it>bioassay system successfully demonstrated that some plant SPO11 orthologues have intrinsic DSB activities. Furthermore, we identified a novel SPO11 homologue, OsSPO11D, with robust DSB activity and a possible meiotic function.</p
Extra Matters Decree the Relatively Heavy Higgs of Mass about 125 GeV in the Supersymmetric Model
We show that the Higgs mass about 125 GeV is easily realized in
supersymmetric model with extra matters, simultaneously explaining the anomaly
in the muon anomalous magnetic moment and the dark matter density.Comment: 10 pages, 2 figures; V2: version accepted for publication of PL
Gravity mediation without a Polonyi problem
Recent indications of the 125GeV Higgs at the LHC can be explained in a
relatively high-scale SUSY scenario where the sparticle masses are multi-TeV as
is realized in the focus-point region. However, it suffers from the notorious
cosmological Polonyi problem. We argue that the Polonyi problem is solved and
thermal or non-thermal leptogenesis scenario works successfully, if a certain
Polonyi coupling to the inflaton is enhanced by a factor of 10-100.Comment: 15 pages, 3 figure
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