591 research outputs found
Domain decomposition improvement of quark propagator estimation
Applying domain decomposition to the lattice Dirac operator and the
associated quark propagator, we arrive at expressions which, with the proper
insertion of random sources therein, can provide improvement to the estimation
of the propagator. Schemes are presented for both open and closed (or loop)
propagators. In the end, our technique for improving open contributions is
similar to the ``maximal variance reduction'' approach of Michael and Peisa,
but contains the advantage, especially for improved actions, of dealing
directly with the Dirac operator. Using these improved open propagators for the
Chirally Improved operator, we present preliminary results for the static-light
meson spectrum. The improvement of closed propagators is modest: on some
configurations there are signs of significant noise reduction of disconnected
correlators; on others, the improvement amounts to a smoothening of the same
correlators.Comment: 19 pages, 8 figures, version to appear in Computer Physics
Communication
Efficient Numerical Evaluation of Feynman Integral
Feynman loop integrals are a key ingredient for the calculation of higher
order radiation effects, and are responsible for reliable and accurate
theoretical prediction. We improve the efficiency of numerical integration in
sector decomposition by implementing a quasi-Monte Carlo method associated with
the CUDA/GPU technique. For demonstration we present the results of several
Feynman integrals up to two loops in both Euclidean and physical kinematic
regions in comparison with those obtained from FIESTA3. It is shown that both
planar and non-planar two-loop master integrals in the physical kinematic
region can be evaluated in less than half a minute with
accuracy, which makes the direct numerical approach viable for precise
investigation of higher order effects in multi-loop processes, e.g. the
next-to-leading order QCD effect in Higgs pair production via gluon fusion with
a finite top quark mass.Comment: 8 pages, 5 figures, published in Chinese Physics
Computational Strategies in Lattice QCD
Lectures given at the Summer School on "Modern perspectives in lattice QCD",
Les Houches, August 3-28, 2009Comment: Latex source, 72 pages, 23 figures; v2: misprints corrected, minor
text change
Status and Future Perspectives for Lattice Gauge Theory Calculations to the Exascale and Beyond
In this and a set of companion whitepapers, the USQCD Collaboration lays out
a program of science and computing for lattice gauge theory. These whitepapers
describe how calculation using lattice QCD (and other gauge theories) can aid
the interpretation of ongoing and upcoming experiments in particle and nuclear
physics, as well as inspire new ones.Comment: 44 pages. 1 of USQCD whitepapers
Lattice QCD with open boundary conditions and twisted-mass reweighting
Lattice QCD simulations at small lattice spacings and quark masses close to
their physical values are technically challenging. In particular, the
simulations can get trapped in the topological charge sectors of field space or
may run into instabilities triggered by accidental near-zero modes of the
lattice Dirac operator. As already noted in ref. [1], the first problem is
bypassed if open boundary conditions are imposed in the time direction, while
the second can potentially be overcome through twisted-mass determinant
reweighting [2]. In this paper, we show that twisted-mass reweighting works out
as expected in QCD with open boundary conditions and 2+1 flavours of O(a)
improved Wilson quarks. Further algorithmic improvements are tested as well and
a few physical quantities are computed for illustration.Comment: Plain TeX source, 27 pages, 7 figure
Topology and Low Lying Fermion Modes
Recent results concerning the relation of topology and low-lying fermion
modes are summarized.Comment: Lattice2001(plenary), 9 pages, 9 figure
Variance Reduction and Cluster Decomposition
It is a common problem in lattice QCD calculation of the mass of the hadron
with an annihilation channel that the signal falls off in time while the noise
remains constant. In addition, the disconnected insertion calculation of the
three-point function and the calculation of the neutron electric dipole moment
with the term suffer from a noise problem due to the
fluctuation. We identify these problems to have the same origin and the
problem can be overcome by utilizing the cluster decomposition
principle. We demonstrate this by considering the calculations of the glueball
mass, the strangeness content in the nucleon, and the CP violation angle in the
nucleon due to the term. It is found that for lattices with physical
sizes of 4.5 - 5.5 fm, the statistical errors of these quantities can be
reduced by a factor of 3 to 4. The systematic errors can be estimated from the
Akaike information criterion. For the strangeness content, we find that the
systematic error is of the same size as that of the statistical one when the
cluster decomposition principle is utilized. This results in a 2 to 3 times
reduction in the overall error.Comment: 7 pages, 5 figures, appendix added to address the systematic erro
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