412 research outputs found
Payload/orbiter contamination control requirement study: Spacelab configuration contamination study
The assessment of the Spacelab carrier induced contaminant environment was continued, and the ability of Spacelab to meet established contamination control criteria for the space transportation system program was determined. The primary areas considered included: (1) updating, refining, and improving the Spacelab contamination computer model and contamination analysis methodology, (2) establishing the resulting adjusted induced environment predictions for comparison with the applicable criteria, (3) determining the Spacelab design and operational requirements necessary to meet the criteria, (4) conducting mission feasibility analyses of the combined Spacelab/Orbiter contaminant environment for specific proposed mission and payload mixes, and (5) establishing a preliminary Spacelab mission support plan as well as model interface requirements; A summary of those activities conducted to date with respect to the modelling, analysis, and predictions of the induced environment, including any modifications in approach or methodology utilized in the contamination assessment of the Spacelab carrier, was presented
Quantization of Field Theories Generalizing Gravity-Yang-Mills Systems on the Cylinder
Pure gravity and gauge theories in two dimensions are shown to be special
cases of a much more general class of field theories each of which is
characterized by a Poisson structure on a finite dimensional target space. A
general scheme for the quantization of these theories is formulated. Explicit
examples are studied in some detail. In particular gravity and gauge theories
with equivalent actions are compared. Big gauge transformations as well as the
condition of metric nondegeneracy in gravity turn out to cause significant
differences in the structure of the corresponding reduced phase spaces and the
quantum spectra of Dirac observables. For gravity coupled to SU(2) Yang
Mills the question of quantum dynamics (`problem of time') is addressed. [This
article is a contribution to the proceedings (to appear in LNP) of the 3rd
Baltic RIM Student Seminar (1993). Importance is attached to concrete examples.
A more abstract presentation of the ideas underlying this article (including
new developments) is found in hep-th/9405110.]Comment: 26, pages, TUW-94-
Topological susceptibility with the asqtad action
Chiral perturbation theory predicts that in quantum chromodynamics (QCD),
light dynamical quarks suppress the gauge-field topological susceptibility of
the vacuum. The degree of suppression depends on quark multiplicity and masses.
It provides a strong consistency test for fermion formulations in lattice QCD.
Such tests are especially important for staggered fermion formulations that
lack a full chiral symmetry and use the "fourth-root" procedure to achieve the
desired number of sea quarks. Over the past few years we have measured the
topological susceptibility on a large database of 18 gauge field ensembles,
generated in the presence of 2+1 flavors of dynamical asqtad quarks with up and
down quark masses ranging from 0.05 to 1 in units of the strange quark mass and
lattice spacings ranging from 0.045 fm to 0.12 fm. Our study also includes
three quenched ensembles with lattice spacings ranging from 0.06 to 0.12 fm. We
construct the topological susceptibility from the integrated point-to-point
correlator of the discretized topological charge density F-Fdual. To reduce its
variance, we model the asymptotic tail of the correlator. The continuum
extrapolation of our results for the topological susceptibility agrees nicely
at small quark mass with the predictions of lowest-order SU(3) chiral
perturbation theory, thus lending support to the validity of the fourth-root
procedure.Comment: 28 pp, 6 figs. Version 2 corrects some discussion, some numbers, and
some figures and adds some reference
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
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
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