13,957 research outputs found
Taste symmetry breaking with HYP-smeared staggered fermions
We study the impact of hypercubic (HYP) smearing on the size of taste
breaking for staggered fermions, comparing to unimproved and to asqtad-improved
staggered fermions. As in previous studies, we find a substantial reduction in
taste-breaking compared to unimproved staggered fermions (by a factor of 4-7 on
lattices with spacing fm). In addition, we observe that
discretization effects of next-to-leading order in the chiral expansion () are markedly reduced by HYP smearing. Compared to asqtad valence
fermions, we find that taste-breaking in the pion spectrum is reduced by a
factor of 2.5-3, down to a level comparable to the expected size of generic
effects. Our results suggest that, once one reaches a lattice
spacing of fm, taste-breaking will be small enough after HYP
smearing that one can use a modified power counting in which , simplify fitting to phenomenologically interesting quantities.Comment: 14 pages, 13 figures, references updated, minor change
Four-point functions and kaon decays in a minimal AdS/QCD model
We study the predictions of holographic QCD for various observable four-point
quark flavour current-current correlators. The dual 5-dimensional bulk theory
we consider is a Yang Mills theory in a slice of
spacetime with boundaries. Particular UV and IR boundary conditions
encode the spontaneous breaking of the dual 4D global chiral symmetry down to
the subgroup. We explain in detail how to calculate the 4D four-point
quark flavour current-current correlators using the 5D holographic theory,
including interactions. We use these results to investigate predictions of
holographic QCD for the rule for kaon decays and the
parameter. The results agree well in comparison with experimental data, with an
accuracy of 25% or better. The holographic theory automatically includes the
contributions of the meson resonances to the four-point correlators. The
correlators agree well in the low-momentum and high-momentum limit, in
comparison with chiral perturbation theory and perturbative QCD results,
respectively.Comment: Published version, title changed to conform with Journal format,
references and clarifying remarks added, 40 pages, 5 figure
BRST symmetry of SU(2) Yang-Mills theory in Cho--Faddeev--Niemi decomposition
We determine the nilpotent BRST and anti-BRST transformations for the
Cho--Faddeev-Niemi variables for the SU(2) Yang-Mills theory based on the new
interpretation given in the previous paper of the Cho--Faddeev-Niemi
decomposition. This gives a firm ground for performing the BRST quantization of
the Yang--Mills theory written in terms of the Cho--Faddeev-Niemi variables. We
propose also a modified version of the new Maximal Abelian gauge which could
play an important role in the reduction to the original Yang-Mills theory.Comment: 11 pages, no figure; Introduction improved, 3 references adde
High Energy Physics from High Performance Computing
We discuss Quantum Chromodynamics calculations using the lattice regulator.
The theory of the strong force is a cornerstone of the Standard Model of
particle physics. We present USQCD collaboration results obtained on Argonne
National Lab's Intrepid supercomputer that deepen our understanding of these
fundamental theories of Nature and provide critical support to frontier
particle physics experiments and phenomenology.Comment: Proceedings of invited plenary talk given at SciDAC 2009, San Diego,
June 14-18, 2009, on behalf of the USQCD collaboratio
Collective resonance modes of Josephson vortices in sandwiched stack of BiSrCaCuO intrinsic Josephson junctions
We observed splitting of the low-bias vortex-flow branch in a
dense-Josephson-vortex state into multiple sub-branches in current-voltage
characteristics of intrinsic Josephson junctions (IJJs) of
BiSrCaCuO single crystals in the long-junction limit.
Each sub-branch corresponds to a plasma mode in serially coupled Josephson
junctions. Splitting into low-bias linear sub-branches with a spread in the
slopes and the inter-sub-branch mode-switching character are in good
quantitative agreement with the prediction of the weak but finite
inter-junction capacitive-coupling model incorporated with the inductive
coupling. This suggests the importance of the role of the capacitive coupling
in accurately describing the vortex dynamics in serially stacked IJJs.Comment: 4 pages, 3 figures, 1 tabl
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