1,627 research outputs found
What Process is Due? Courts and Science-Policy Disputes
A Review of What Process is Due? Courts and Science-Policy Disputes by David M. O\u27Brie
The Phase Diagram of High Temperature QCD with Three Flavors of Improved Staggered Quarks
We report on progress in our study of high temperature QCD with three flavors
of improved staggered quarks. Simulations are being carried out with three
degenerate quarks with masses less than or equal to the strange quark mass,
, and with degenerate up and down quarks with masses in the range , and the strange quark mass fixed near its physical
value. For the quark masses studied to date we find rapid crossovers, which
sharpen as the quark mass is reduced, rather than bona fide phase transitions.Comment: Lattice 2003 (Nonzero temperature and density
The scaling dimension of low lying Dirac eigenmodes and of the topological charge density
As a quantitative measure of localization, the inverse participation ratio of
low lying Dirac eigenmodes and topological charge density is calculated on
quenched lattices over a wide range of lattice spacings and volumes. Since
different topological objects (instantons, vortices, monopoles, and artifacts)
have different co-dimension, scaling analysis provides information on the
amount of each present and their correlation with the localization of low lying
eigenmodes.Comment: Lattice2004(topology), Fermilab, June 21 - 26, 2004; 3 pages, 3
figure
Light pseudoscalar decay constants, quark masses, and low energy constants from three-flavor lattice QCD
As part of our program of lattice simulations of three flavor QCD with
improved staggered quarks, we have calculated pseudoscalar meson masses and
decay constants for a range of valence quark masses and sea quark masses on
lattices with lattice spacings of about 0.125 fm and 0.09 fm. We fit the
lattice data to forms computed with staggered chiral perturbation theory. Our
results provide a sensitive test of the lattice simulations, and especially of
the chiral behavior, including the effects of chiral logarithms. We find:
f_\pi=129.5(0.9)(3.5)MeV, f_K=156.6(1.0)(3.6)MeV, and f_K/f_\pi=1.210(4)(13),
where the errors are statistical and systematic. Following a recent paper by
Marciano, our value of f_K/f_\pi implies |V_{us}|=0.2219(26). Further, we
obtain m_u/m_d= 0.43(0)(1)(8), where the errors are from statistics, simulation
systematics, and electromagnetic effects, respectively. The data can also be
used to determine several of the constants of the low energy effective
Lagrangian: in particular we find 2L_8-L_5=-0.2(1)(2) 10^{-3} at chiral scale
m_\eta. This provides an alternative (though not independent) way of estimating
m_u; 2L_8-L_5 is far outside the range that would allow m_u=0. Results for
m_s^\msbar, \hat m^\msbar, and m_s/\hat m can be obtained from the same lattice
data and chiral fits, and have been presented previously in joint work with the
HPQCD and UKQCD collaborations. Using the perturbative mass renormalization
reported in that work, we obtain m_u^\msbar=1.7(0)(1)(2)(2)MeV and
m_d^\msbar=3.9(0)(1)(4)(2)MeV at scale 2 GeV, with errors from statistics,
simulation, perturbation theory, and electromagnetic effects, respectively.Comment: 86 pages, 22 figures. v3: Remarks about m_u=0 and the strong CP
problem modified; reference added. Figs 5--8 modified for clarity. Version to
be published in Phys. Rev. D. v2: Expanded discussion of finite volume
effects, normalization in Table I fixed, typos and minor errors correcte
Light hadrons with improved staggered quarks: approaching the continuum limit
We have extended our program of QCD simulations with an improved
Kogut-Susskind quark action to a smaller lattice spacing, approximately 0.09
fm. Also, the simulations with a approximately 0.12 fm have been extended to
smaller quark masses. In this paper we describe the new simulations and
computations of the static quark potential and light hadron spectrum. These
results give information about the remaining dependences on the lattice
spacing. We examine the dependence of computed quantities on the spatial size
of the lattice, on the numerical precision in the computations, and on the step
size used in the numerical integrations. We examine the effects of
autocorrelations in "simulation time" on the potential and spectrum. We see
effects of decays, or coupling to two-meson states, in the 0++, 1+, and 0-
meson propagators, and we make a preliminary mass computation for a radially
excited 0- meson.Comment: 43 pages, 16 figure
High-Precision Lattice QCD Confronts Experiment
We argue that high-precision lattice QCD is now possible, for the first time,
because of a new improved staggered quark discretization. We compare a wide
variety of nonperturbative calculations in QCD with experiment, and find
agreement to within statistical and systematic errors of 3% or less. We also
present a new determination of alpha_msbar(Mz); we obtain 0.121(3). We discuss
the implications of this breakthrough for phenomenology and, in particular, for
heavy-quark physics.Comment: 2 figures, revte
Full nonperturbative QCD simulations with 2+1 flavors of improved staggered quarks
Dramatic progress has been made over the last decade in the numerical study
of quantum chromodynamics (QCD) through the use of improved formulations of QCD
on the lattice (improved actions), the development of new algorithms and the
rapid increase in computing power available to lattice gauge theorists. In this
article we describe simulations of full QCD using the improved staggered quark
formalism, ``asqtad'' fermions. These simulations were carried out with two
degenerate flavors of light quarks (up and down) and with one heavier flavor,
the strange quark. Several light quark masses, down to about 3 times the
physical light quark mass, and six lattice spacings have been used. These
enable controlled continuum and chiral extrapolations of many low energy QCD
observables. We review the improved staggered formalism, emphasizing both
advantages and drawbacks. In particular, we review the procedure for removing
unwanted staggered species in the continuum limit. We then describe the asqtad
lattice ensembles created by the MILC Collaboration. All MILC lattice ensembles
are publicly available, and they have been used extensively by a number of
lattice gauge theory groups. We review physics results obtained with them, and
discuss the impact of these results on phenomenology. Topics include the heavy
quark potential, spectrum of light hadrons, quark masses, decay constant of
light and heavy-light pseudoscalar mesons, semileptonic form factors, nucleon
structure, scattering lengths and more. We conclude with a brief look at highly
promising future prospects.Comment: 157 pages; prepared for Reviews of Modern Physics. v2: some rewriting
throughout; references update
Lattice calculation of hybrid mesons with improved Kogut-Susskind fermions
We report on a lattice determination of the mass of the exotic
hybrid meson using an improved Kogut-Susskind action. Results from both
quenched and dynamical quark simulations are presented. We also compare with
earlier results using Wilson quarks at heavier quark masses. The results on
lattices with three flavors of dynamical quarks show effects of sea quarks on
the hybrid propagators which probably result from coupling to two meson states.
We extrapolate the quenched results to the physical light quark mass to allow
comparison with experimental candidates for the hybrid meson. The
lattice result remains somewhat heavier than the experimental result, although
it may be consistent with the .Comment: 24 pages, 12 figures. Replaced to match published versio
Waning efficacy in a long-term AAV-mediated gene therapy study in the murine model of Krabbe disease
Neonatal AAV9-gene therapy of the lysosomal enzyme galactosylceramidase (GALC) significantly ameliorates central and peripheral neuropathology, prolongs survival, and largely normalizes motor deficits in Twitcher mice. Despite these therapeutic milestones, new observations identified the presence of multiple small focal demyelinating areas in the brain after 6-8 months. These lesions are in stark contrast to the diffuse, global demyelination that affects the brain of naive Twitcher mice. Late-onset lesions exhibited lysosomal alterations with reduced expression of GALC and increased psychosine levels. Furthermore, we found that lesions were closely associated with the extravasation of plasma fibrinogen and activation of the fibrinogen-BMP-SMAD-GFAP gliotic response. Extravasation of fibrinogen correlated with tight junction disruptions of the vasculature within the lesioned areas. The lesions were surrounded by normal appearing white matter. Our study shows that the dysregulation of therapeutic GALC was likely driven by the exhaustion of therapeutic AAV episomal DNA within the lesions, paralleling the presence of proliferating oligodendrocyte progenitors and glia. We believe that this is the first demonstration of diminishing expression in vivo from an AAV gene therapy vector with detrimental effects in the brain of a lysosomal storage disease animal model. The development of this phenotype linking localized loss of GALC activity with relapsing neuropathology in the adult brain of neonatally AAV-gene therapy-treated Twitcher mice identifies and alerts to possible late-onset reductions of AAV efficacy, with implications to other genetic leukodystrophies
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