23 research outputs found
Status of and performance estimates for QCDOC
QCDOC is a supercomputer designed for high scalability at a low cost per
node. We discuss the status of the project and provide performance estimates
for large machines obtained from cycle accurate simulation of the QCDOC ASIC.Comment: 3 pages 1 figure. Lattice2002(machines
Chirality Correlation within Dirac Eigenvectors from Domain Wall Fermions
In the dilute instanton gas model of the QCD vacuum, one expects a strong
spatial correlation between chirality and the maxima of the Dirac eigenvectors
with small eigenvalues. Following Horvath, {\it et al.} we examine this
question using lattice gauge theory within the quenched approximation. We
extend the work of those authors by using weaker coupling, , larger
lattices, , and an improved fermion formulation, domain wall fermions. In
contrast with this earlier work, we find a striking correlation between the
magnitude of the chirality density, , and the
normal density, , for the low-lying Dirac eigenvectors.Comment: latex, 25 pages including 12 eps figure
Nonperturbative bound on high multiplicity cross sections in phi^4_3 from lattice simulation
We have looked for evidence of large cross sections at large multiplicities
in weakly coupled scalar field theory in three dimensions. We use spectral
function sum rules to derive bounds on total cross sections where the sum can
be expresed in terms of a quantity which can be measured by Monte Carlo
simulation in Euclidean space. We find that high multiplicity cross sections
remain small for energies and multiplicities for which large effects had been
suggested.Comment: 23 pages, revtex, seven eps figures revised version: typos corrected,
some rewriting of discusion, same resul
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
Direct CP violation and the ΔI=1/2 rule in K→ππ decay from the standard model
We present a lattice QCD calculation of the ΔI=1/2, K→ππ decay amplitude A0 and ϵ′, the measure of direct CP violation in K→ππ decay, improving our 2015 calculation [1] of these quantities. Both calculations were performed with physical kinematics on a 323×64 lattice with an inverse lattice spacing of a-1=1.3784(68) GeV. However, the current calculation includes nearly 4 times the statistics and numerous technical improvements allowing us to more reliably isolate the ππ ground state and more accurately relate the lattice operators to those defined in the standard model. We find Re(A0)=2.99(0.32)(0.59)×10-7 GeV and Im(A0)=-6.98(0.62)(1.44)×10-11 GeV, where the errors are statistical and systematic, respectively. The former agrees well with the experimental result Re(A0)=3.3201(18)×10-7 GeV. These results for A0 can be combined with our earlier lattice calculation of A2 [2] to obtain Re(ϵ′/ϵ)=21.7(2.6)(6.2)(5.0)×10-4, where the third error represents omitted isospin breaking effects, and Re(A0)/Re(A2)=19.9(2.3)(4.4). The first agrees well with the experimental result of Re(ϵ′/ϵ)=16.6(2.3)×10-4. A comparison of the second with the observed ratio Re(A0)/Re(A2)=22.45(6), demonstrates the standard model origin of this “ΔI=1/2 rule” enhancement.We present a lattice QCD calculation of the , decay amplitude and , the measure of direct CP-violation in decay, improving our 2015 calculation of these quantities. Both calculations were performed with physical kinematics on a lattice with an inverse lattice spacing of GeV. However, the current calculation includes nearly four times the statistics and numerous technical improvements allowing us to more reliably isolate the ground-state and more accurately relate the lattice operators to those defined in the Standard Model. We find GeV and GeV, where the errors are statistical and systematic, respectively. The former agrees well with the experimental result GeV. These results for can be combined with our earlier lattice calculation of to obtain , where the third error represents omitted isospin breaking effects, and Re/Re. The first agrees well with the experimental result of . A comparison of the second with the observed ratio ReRe, demonstrates the Standard Model origin of this " rule" enhancement
Quenched Lattice QCD with Domain Wall Fermions and the Chiral Limit
Quenched QCD simulations on three volumes, , and
and three couplings, , 5.85 and 6.0 using domain
wall fermions provide a consistent picture of quenched QCD. We demonstrate that
the small induced effects of chiral symmetry breaking inherent in this
formulation can be described by a residual mass (\mres) whose size decreases
as the separation between the domain walls () is increased. However, at
stronger couplings much larger values of are required to achieve a given
physical value of \mres. For and , we find
\mres/m_s=0.033(3), while for , and ,
\mres/m_s=0.074(5), where is the strange quark mass. These values are
significantly smaller than those obtained from a more naive determination in
our earlier studies. Important effects of topological near zero modes which
should afflict an accurate quenched calculation are easily visible in both the
chiral condensate and the pion propagator. These effects can be controlled by
working at an appropriately large volume. A non-linear behavior of in
the limit of small quark mass suggests the presence of additional infrared
subtlety in the quenched approximation. Good scaling is seen both in masses and
in over our entire range, with inverse lattice spacing varying between
1 and 2 GeV.Comment: 91 pages, 34 figure
The SU(2) and SU(3) chiral phase transitions within Chiral Perturbation Theory
The SU(2) and SU(3) chiral phase transitions in a hot gas made of pions,
kaons and etas are studied within the framework of Chiral Perturbation Theory.
By using the meson meson scattering phase shifts in a second order virial
expansion, we are able to describe the temperature dependence of the quark
condensates. We have estimated the critical temperatures where the different
condensates melt. In particular, the SU(3) formalism yields a lower critical
temperature for the non-strange condensates than within SU(2), and also
suggests that the strange condensate may melt at a somewhat higher temperature,
due to the different strange and non-strange quark masses.Comment: 4 pages, two figures. Final version to appear in Phys Rev D. Complete
model independent calculation. Unitarized ChPt only used to check
extrapolation at high T. References added and numerical bug correcte
Computational Physics on Graphics Processing Units
The use of graphics processing units for scientific computations is an
emerging strategy that can significantly speed up various different algorithms.
In this review, we discuss advances made in the field of computational physics,
focusing on classical molecular dynamics, and on quantum simulations for
electronic structure calculations using the density functional theory, wave
function techniques, and quantum field theory.Comment: Proceedings of the 11th International Conference, PARA 2012,
Helsinki, Finland, June 10-13, 201
Pi-eta scattering and the resummation of vacuum fluctuation in three-flavour ChPT
We discuss various aspects of resummed chiral perturbation theory, which was
developed recently in order to consistently include the possibility of large
vacuum fluctuations of the ss-pairs and the scenario with smaller value of the
chiral condensate for N_f=3. The subtleties of this approach are illustrated
using a concrete example of observables connected with pi-eta scattering. This
process seems to be a suitable theoretical laboratory for this purpose due to
its sensitivity to the values of the O(p^4) LEC's, namely to the values of the
fluctuation parameters L4 and L6. We discuss several issues in detail, namely
the choice of `good' observables and properties of their bare expansions, the
`safe' reparametrization in terms of physical observables, the implementation
of exact perturbative unitarity and exact renormalization scale independence,
the role of higher order remainders and their estimates. We make a detailed
comparison with standard chiral perturbation theory and use generalized ChPT as
well as resonance chiral theory to estimate the higher order remainders.Comment: Version submitted to EPJ