3,517 research outputs found
Unexpected Spin-Off from Quantum Gravity
We propose a novel way of investigating the universal properties of spin
systems by coupling them to an ensemble of causal dynamically triangulated
lattices, instead of studying them on a fixed regular or random lattice.
Somewhat surprisingly, graph-counting methods to extract high- or
low-temperature series expansions can be adapted to this case. For the
two-dimensional Ising model, we present evidence that this ameliorates the
singularity structure of thermodynamic functions in the complex plane, and
improves the convergence of the power series.Comment: 10 pages, 4 figures; final, slightly amended version, to appear in
Physica
The Decay Amplitude from Lattice QCD
We report on the first realistic \emph{ab initio} calculation of a hadronic
weak decay, that of the amplitude for a kaon to decay into two \pi-mesons
with isospin 2. We find Re in good agreement with the
experimental result and for the hitherto unknown imaginary part we find
{Im}. Moreover combining our result for
Im\, with experimental values of Re\,, Re\, and
, we obtain the following value for the unknown ratio
Im\,/Re\, within the Standard Model:
.
One consequence of these results is that the contribution from Im\, to the
direct CP violation parameter (the so-called Electroweak
Penguin, EWP, contribution) is Re. We
explain why this calculation of represents a major milestone for lattice
QCD and discuss the exciting prospects for a full quantitative understanding of
CP-violation in kaon decays.Comment: 5 pages, 1 figur
QCDOC: A 10-teraflops scale computer for lattice QCD
The architecture of a new class of computers, optimized for lattice QCD
calculations, is described. An individual node is based on a single integrated
circuit containing a PowerPC 32-bit integer processor with a 1 Gflops 64-bit
IEEE floating point unit, 4 Mbyte of memory, 8 Gbit/sec nearest-neighbor
communications and additional control and diagnostic circuitry. The machine's
name, QCDOC, derives from ``QCD On a Chip''.Comment: Lattice 2000 (machines) 8 pages, 4 figure
Lattice determination of the Decay Amplitude
We describe the computation of the amplitude A_2 for a kaon to decay into two
pions with isospin I=2. The results presented in the letter Phys.Rev.Lett. 108
(2012) 141601 from an analysis of 63 gluon configurations are updated to 146
configurations giving Re GeV and Im
GeV. Re is in good agreement with the experimental result, whereas the
value of Im was hitherto unknown. We are also working towards a direct
computation of the amplitude but, within the
standard model, our result for Im can be combined with the experimental
results for Re, Re and to give
ImRe . Our result for Im\, implies
that the electroweak penguin (EWP) contribution to
is Re.Comment: 59 pages, 11 figure
The Kaon B-parameter from Quenched Domain-Wall QCD
We present numerical results for the kaon B-parameter, B_K, determined in the
quenched approximation of lattice QCD. Our simulations are performed using
domain-wall fermions and the renormalization group improved, DBW2 gauge action
which combine to give quarks with good chiral symmetry at finite lattice
spacing. Operators are renormalized non-perturbatively using the RI/MOM scheme.
We study scaling by performing the simulation on two different lattices with
a^{-1} = 1.982(30) and 2.914(54) GeV. We combine this quenched scaling study
with an earlier calculation of B_K using two flavors of dynamical, domain-wall
quarks at a single lattice spacing to obtain
B_K(MS,NDR,mu=2GeV)=0.563(21)(39)(30), were the first error is statistical, the
second systematic (without quenching errors) and the third estimates the error
due to quenching.Comment: 77 pages, 44 figures, to be published in Phys. Rev.
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