287 research outputs found
Low-lying Wilson Dirac operator eigenvector mixing in dynamical overlap Hybrid Monte-Carlo
Current dynamical overlap fermion hybrid Monte Carlo simulations encounter
large fermionic forces when there is mixing between near zero-eigenvectors of
the kernel operator. This leads to low acceptance rates when there is a large
density of near zero eigenvectors. I present a method where these large forces
are eliminated and the large action jumps seen when two eigenvectors approach
zero are significantly reduced. This significantly increases the stability of
the algorithm, and allows the use of larger integration time steps.Comment: 20 Pages, 4 figures; v2 with minor modifications; v3 further minor
modifications, as accepted by Computer Physics Communication
Numerical Methods for the QCD Overlap Operator IV: Hybrid Monte Carlo
The extreme computational costs of calculating the sign of the Wilson matrix
within the overlap operator have so far prevented four dimensional dynamical
overlap simulations on realistic lattice sizes, because the computational power
required to invert the overlap operator, the time consuming part of the Hybrid
Monte Carlo algorithm, is too high. In this series of papers we introduced the
optimal approximation of the sign function and have been developing
preconditioning and relaxation techniques which reduce the time needed for the
inversion of the overlap operator by over a factor of four, bringing the
simulation of dynamical overlap fermions on medium-size lattices within the
range of Teraflop-computers.
In this paper we adapt the HMC algorithm to overlap fermions. We approximate
the matrix sign function using the Zolotarev rational approximation, treating
the smallest eigenvalues of the Wilson operator exactly within the fermionic
force. We then derive the fermionic force for the overlap operator, elaborating
on the problem of Dirac delta-function terms from zero crossings of eigenvalues
of the Wilson operator. The crossing scheme proposed shows energy violations
which are better than O() and thus are comparable with the
violations of the standard leapfrog algorithm over the course of a trajectory.
We explicitly prove that our algorithm satisfies reversibility and area
conservation. Finally, we test our algorithm on small , , and
lattices at large masses.Comment: v2 60 pages; substantial changes to all parts of the article; v3
minor revsion
Localization and chiral symmetry in 2+1 flavor domain wall QCD
We present results for the dependence of the residual mass of domain wall
fermions (DWF) on the size of the fifth dimension and its relation to the
density and localization properties of low-lying eigenvectors of the
corresponding hermitian Wilson Dirac operator relevant to simulations of 2+1
flavor domain wall QCD. Using the DBW2 and Iwasaki gauge actions, we generate
ensembles of configurations with a space-time volume and an
extent of 8 in the fifth dimension for the sea quarks. We demonstrate the
existence of a regime where the degree of locality, the size of chiral symmetry
breaking and the rate of topology change can be acceptable for inverse lattice
spacings GeV.Comment: 59 Pages, 23 figures, 1 MPG linke
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
Nucleon strange quark content from two-flavor lattice QCD with exact chiral symmetry
Strange quark content of the nucleon is calculated in dynamical lattice QCD
employing the overlap fermion formulation. For this quantity, exact chiral
symmetry guaranteed by the Ginsparg-Wilson relation is crucial to avoid large
contamination due to a possible operator mixing with . Gauge
configurations are generated with two dynamical flavors on a 16^3 x 32 lattice
at a lattice spacing a \simeq 0.12fm. We directly calculate the relevant
three-point function on the lattice including a disconnected strange quark loop
utilizing the techniques of all-to-all quark propagator and low-mode averaging.
Our result f_{T_s} = 0.032(8)(22), is in good agreement with our previous
indirect estimate using the Feynman-Hellmann theorem.Comment: 31 pages, 22 figures; version published in PR
Study of instanton physics in lattice QCD
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1997.Includes bibliographical references (p. 91-96).by Taras Ivanenko.Ph.D
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