317 research outputs found
Physical Point Simulation in 2+1 Flavor Lattice QCD
We present the results of the physical point simulation in 2+1 flavor lattice
QCD with the nonperturbatively -improved Wilson quark action and the
Iwasaki gauge action at on a
lattice. The physical quark masses together with the lattice
spacing is determined with , and as physical inputs.
There are two key algorithmic ingredients to make possible the direct
simulation at the physical point: One is the mass-preconditioned
domain-decomposed HMC algorithm to reduce the computational cost. The other is
the reweighting technique to adjust the hopping parameters exactly to the
physical point. The physics results include the hadron spectrum, the quark
masses and the pseudoscalar meson decay constants. The renormalization factors
are nonperturbatively evaluated with the Schr{\"o}dinger functional method. The
results are compared with the previous ones obtained by the chiral
extrapolation method.Comment: 20 pages, 17 figures, version to appear in Phys. Rev.
Application of heavy-quark effective theory to lattice QCD: II. Radiative corrections to heavy-light currents
We apply heavy-quark effective theory to separate long- and short-distance
effects of heavy quarks in lattice gauge theory. In this approach, the inverse
heavy-quark mass and the lattice spacing are treated as short distances, and
their effects are lumped into short-distance coefficients. We show how to use
this formalism to match lattice gauge theory to continuum QCD, order by order
in the heavy-quark expansion. In this paper, we focus on heavy-light currents.
In particular, we obtain one-loop results for the matching factors of lattice
currents, needed for heavy-quark phenomenology, such as the calculation of
heavy-light decay constants, and heavy-to-light transition form factors.
Results for the Brodsky-Lepage-Mackenzie scale are also given.Comment: 32 pages, 8 figures. v2 corrects Eqs. (4.9) and (4.10) and adds a
reference. Program LatHQ2QCD to compute matching one-loop coefficients
available at http://theory.fnal.gov/people/kronfeld/LatHQ2QCD
Flavor Singlet Meson Mass in the Continuum Limit in Two-Flavor Lattice QCD
We present results for the mass of the eta-prime meson in the continuum limit
for two-flavor lattice QCD, calculated on the CP-PACS computer, using a
renormalization-group improved gauge action, and Sheikholeslami and Wohlert's
fermion action with tadpole-improved csw. Correlation functions are measured at
three values of the coupling constant beta corresponding to the lattice spacing
a approx. 0.22, 0.16, 0.11 fm and for four values of the quark mass parameter
kappa corresponding to mpi over mrho approx. 0.8, 0.75, 0.7 and 0.6. For each
beta, kappa pair, 400-800 gauge configurations are used. The two-loop diagrams
are evaluated using a noisy source method. We calculate eta-prime propagators
using local sources, and find that excited state contributions are much reduced
by smearing. A full analysis for the smeared propagators gives
metaprime=0.960(87)+0.036-0.248 GeV, in the continuum limit, where the second
error represents the systematic uncertainty coming from varying the functional
form for chiral and continuum extrapolations.Comment: 9 pages, 19 figures, 4 table
Bulk Electronic structure of NaCoO.1.3HO
High-energy (h = 5.95 keV) synchrotron Photoemission spectroscopy (PES)
is used to study bulk electronic structure of NaCoO.1.3HO,
the layered superconductor. In contrast to 3-dimensional doped Co oxides, Co
core level spectra show well-separated Co and Co ions.
Cluster calculations suggest low spin Co and Co character, and a
moderate on-site Coulomb correlation energy U3-5.5 eV. Photon
dependent valence band PES identifies Co and O derived
states, in near agreement with band structure calculations.Comment: 4 pages 4 figures Revised text added referenc
Connexin-43 prevents hematopoietic stem cell senescence through transfer of reactive oxygen species to bone marrow stromal cells
Hematopoietic stem cell (HSC) aging has become a concern in chemotherapy of older patients. Humoral and paracrine signals from the bone marrow (BM) hematopoietic microenvironment (HM) control HSC activity during regenerative hematopoiesis. Connexin-43 (Cx43), a connexin constituent of gap junctions (GJs) is expressed in HSCs, down-regulated during differentiation, and postulated to be a self-renewal gene. Our studies, however, reveal that hematopoietic-specific Cx43 deficiency does not result in significant long-term competitive repopulation deficiency. Instead, hematopoietic Cx43 (H-Cx43) deficiency delays hematopoietic recovery after myeloablation with 5-fluorouracil (5-FU). 5-FU-treated H-Cx43-deficient HSC and progenitors (HSC/P) cells display decreased survival and fail to enter the cell cycle to proliferate. Cell cycle quiescence is associated with down-regulation of cyclin D1, up-regulation of the cyclin-dependent kinase inhibitors, p21cip1. and p16INK4a, and Forkhead transcriptional factor 1 (Foxo1), and activation of p38 mitogen-activated protein kinase (MAPK), indicating that H-Cx43-deficient HSCs are prone to senescence. The mechanism of increased senescence in H-Cx43-deficient HSC/P cells depends on their inability to transfer reactive oxygen species (ROS) to the HM, leading to accumulation of ROS within HSCs. In vivo antioxidant administration prevents the defective hematopoietic regeneration, as well as exogenous expression of Cx43 in HSC/P cells. Furthermore, ROS transfer from HSC/P cells to BM stromal cells is also rescued by reexpression of Cx43 in HSC/P. Finally, the deficiency of Cx43 in the HM phenocopies the hematopoietic defect in vivo. These results indicate that Cx43 exerts a protective role and regulates the HSC/P ROS content through ROS transfer to the HM, resulting in HSC protection during stress hematopoietic regeneration
Measurement of the direct asymmetry in decays with a lepton tag
We report the measurement of the direct asymmetry in the radiative
decay using a data sample of pairs collected at the resonance with
the Belle detector at the KEKB asymmetric-energy collider. The
asymmetry is measured as a function of the photon energy threshold. For
, where is the
photon energy in the center-of-mass frame, we obtain
,
consistent with the Standard Model prediction.Comment: Published at PR
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