12,577 research outputs found
Hardware and software status of QCDOC
QCDOC is a massively parallel supercomputer whose processing nodes are based
on an application-specific integrated circuit (ASIC). This ASIC was
custom-designed so that crucial lattice QCD kernels achieve an overall
sustained performance of 50% on machines with several 10,000 nodes. This strong
scalability, together with low power consumption and a price/performance ratio
of $1 per sustained MFlops, enable QCDOC to attack the most demanding lattice
QCD problems. The first ASICs became available in June of 2003, and the testing
performed so far has shown all systems functioning according to specification.
We review the hardware and software status of QCDOC and present performance
figures obtained in real hardware as well as in simulation.Comment: Lattice2003(machine), 6 pages, 5 figure
Electron heating mechanisms in dual frequency capacitive discharges
We discuss electron heating mechanisms in the sheath regions of dual-frequency capacitive discharges, with the twin aims of identifying the dominant mechanisms and supplying closed-form expressions from which the heating power can be estimated. We show that the heating effect produced by either Ohmic or collisionless heating is much larger when the discharge is excited by a superposition of currents at two frequencies than if either current had acted alone. This coupling effect occurs because the lower frequency current, while not directly heating the electrons to any great extent, strongly affects the spatial structure of the discharge in the sheath regions
Canister closing device Patent
Design and characteristics of device for closing canisters under high vacuum condition
Opening the Rome-Southampton window for operator mixing matrices
We show that the running of operators which mix under renormalization can be
computed fully non-perturbatively as a product of continuum step scaling
matrices. These step scaling matrices are obtained by taking the "ratio" of Z
matrices computed at different energies in an RI-MOM type scheme for which
twisted boundary conditions are an essential ingredient. Our method allows us
to relax the bounds of the Rome-Southampton window. We also explain why such a
method is important in view of the light quark physics program of the RBC-UKQCD
collaborations. To illustrate our method, using n_f=2+1 domain-wall fermions,
we compute the non-perturbative running matrix of four-quark operators needed
in K->pipi decay and neutral kaon mixing. Our results are then compared to
perturbation theory.Comment: 8 pages, 7 figures. v2: PRD version, minor changes and few references
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Hadronic contribution to the muon g-2: a theoretical determination
The leading order hadronic contribution to the muon g-2, , is
determined entirely from theory using an approach based on Cauchy's theorem in
the complex squared energy s-plane. This is possible after fitting the
integration kernel in with a simpler function of . The
integral determining in the light-quark region is then split
into a low energy and a high energy part, the latter given by perturbative QCD
(PQCD). The low energy integral involving the fit function to the integration
kernel is determined by derivatives of the vector correlator at the origin,
plus a contour integral around a circle calculable in PQCD. These derivatives
are calculated using hadronic models in the light-quark sector. A similar
procedure is used in the heavy-quark sector, except that now everything is
calculable in PQCD, thus becoming the first entirely theoretical calculation of
this contribution. Using the dual resonance model realization of Large
QCD to compute the derivatives of the correlator leads to agreement with the
experimental value of . Accuracy, though, is currently limited by the
model dependent calculation of derivatives of the vector correlator at the
origin. Future improvements should come from more accurate chiral perturbation
theory and/or lattice QCD information on these derivatives, allowing for this
method to be used to determine accurately entirely from theory,
independently of any hadronic model.Comment: Several additional clarifying paragraphs have been added. 1/N_c
corrections have been estimated. No change in result
Proton lifetime bounds from chirally symmetric lattice QCD
We present results for the matrix elements relevant for proton decay in Grand
Unified Theories (GUTs). The calculation is performed at a fixed lattice
spacing a^{-1}=1.73(3) GeV using 2+1 flavors of domain wall fermions on
lattices of size 16^3\times32 and 24^3\times64 with a fifth dimension of length
16. We use the indirect method which relies on an effective field theory
description of proton decay, where we need to estimate the low energy
constants, \alpha = -0.0112(25) GeV^3 and \beta = 0.0120(26) GeV^3. We relate
these low energy constants to the proton decay matrix elements using leading
order chiral perturbation theory. These can then be combined with experimental
bounds on the proton lifetime to bound parameters of individual GUTs.Comment: 17 pages, 9 Figure
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