78 research outputs found
Continuum EoS for QCD with Nf=2+1 flavors
We report on a continuum extrapolated result [arXiv:1309.5258] for the
equation of state (EoS) of QCD with dynamical quark flavors. In this
study, all systematics are controlled, quark masses are set to their physical
values, and the continuum limit is taken using at least three lattice spacings
corresponding to temporal extents up to . A Symanzik improved gauge and
stout-link improved staggered fermion action is used. Our results are available
online [ancillary file to arXiv:1309.5258].Comment: Conference proceedings, 7 pages, 4 figures. Talk presented at 31st
International Symposium on Lattice Field Theory (LATTICE 2013), July 29 -
August 3, 2013, Mainz, German
QCD transition temperature: full staggered result
We conclude our investigations on the QCD cross-over transition temperatures
with 2+1 staggered flavours and one-link stout improvement. We extend our
previous two studies [Phys. Lett. B643 (2006) 46, JHEP 0906:088 (2009)] by
choosing even finer lattices (N_t=16) and we work again with physical quark
masses. These new results [for details see JHEP 1009:073,2010] support our
earlier findings. We compare them with the published results of the hotQCD
collaboration. All these results are confronted with the predictions of the
Hadron Resonance Gas model and Chiral Perturbation Theory for temperatures
below the transition region. Our results can be reproduced by using the
physical spectrum. The findings of the hotQCD collaboration can be recovered
only by using a distorted spectrum. This analysis provides a simple explanation
for the observed discrepancy in the transition T between our and the hotQCD
collaborations.Comment: presented at the XXVIII. International Symposium on Lattice Field
Theory, June 14-19,2010, Villasimius, Sardinia Ital
Recent results on the Equation of State of QCD
We report on a continuum extrapolated result (arXiv:1309.5258) for the
equation of state (EoS) of QCD with dynamical quark flavors and
discuss preliminary results obtained with an additional dynamical charm quark
(). For all our final results, the systematics are controlled, quark
masses are set to their physical values, and the continuum limit is taken using
at least three lattice spacings corresponding to temporal extents up to
.Comment: Conference proceedings: The 32nd International Symposium on Lattice
Field Theory - Lattice 2014, June 23-28, 2014, Columbia University, New York,
New Yor
Chiral behavior of pseudo-Goldstone boson masses and decay constants in 2+1 flavor QCD
We present preliminary results for the chiral behavior of charged
pseudo-Goldstone-boson masses and decay constants. These are obtained in
simulations with N_f=2+1 flavors of tree-level, O(a)-improved Wilson sea
quarks. In these simulations, mesons are composed of either valence quarks
discretized in the same way as the sea quarks (unitary simulations) or of
overlap valence quarks (mixed-action simulations). We find that the chiral
behavior of the pseudoscalar meson masses in the mixed-action calculations
cannot be explained with continuum, partially-quenched chiral perturbation
theory. We show that the inclusion of O(a^2) unitarity violations in the chiral
expansion resolves this discrepancy and that the size of the unitarity
violations required are consistent with those which we observe in the
zero-momentum, scalar-isotriplet-meson propagator.Comment: 7 pages, 3 figures, talk by L. Lellouch at the XXV International
Symposium on Lattice Field Theory (LATTICE 2007), 30 July - 4 August 2007,
Regensburg, German
The ratio FK/Fpi in QCD
We determine the ratio FK/Fpi in QCD with Nf=2+1 flavors of sea quarks, based
on a series of lattice calculations with three different lattice spacings,
large volumes and a simulated pion mass reaching down to about 190 MeV. We
obtain FK/Fpi=1.192 +/- 0.007(stat) +/- 0.006(syst). This result is then used
to give an updated value of the CKM matrix element |Vus|. The unitarity
relation for the first row of this matrix is found to be well observed.Comment: 15 pages, 4 figures, 2 table
Scaling study for 2 HEX smeared fermions: hadron and quark masses
The goal of this study is to investigate the scaling behaviour of our 2 HEX
action. For this purpose, we compute the spectrum and compare the
results to our 6 EXP action. We find a large scaling window up to along with small scaling corrections at the 2%-level and
full compatibility with our previous study. As a second important observable to
be tested for scaling, we chose the non-perturbatively renormalized quenched
strange quark mass. Here we find a fairly flat scaling with a broad scaling
range up to and perfect agreement with the
literature.Comment: PoS for the XXVIII International Symposium on Lattice Field Theory,
Lattice2010, 7 pages, 4 figure
Lattice QCD as a video game
The speed, bandwidth and cost characteristics of today's PC graphics cards make them an attractive target as general purpose computational platforms. High performance can be achieved also for lattice simulations but the actual implementation can be cumbersome. This paper outlines the architecture and programming model of modern graphics cards for the lattice practitioner with the goal of exploiting these chips for Monte Carlo simulations. Sample code is also given. (c) 2007 Elsevier B.V. All rights reserved
Precision computation of the kaon bag parameter
Indirect CP violation in K \rightarrow {\pi}{\pi} decays plays a central role
in constraining the flavor structure of the Standard Model (SM) and in the
search for new physics. For many years the leading uncertainty in the SM
prediction of this phenomenon was the one associated with the nonperturbative
strong interaction dynamics in this process. Here we present a fully controlled
lattice QCD calculation of these effects, which are described by the neutral
kaon mixing parameter B_K . We use a two step HEX smeared clover-improved
Wilson action, with four lattice spacings from a\approx0.054 fm to
a\approx0.093 fm and pion masses at and even below the physical value.
Nonperturbative renormalization is performed in the RI-MOM scheme, where we
find that operator mixing induced by chiral symmetry breaking is very small.
Using fully nonperturbative continuum running, we obtain our main result
B_K^{RI}(3.5GeV)=0.531(6)_{stat}(2)_{sys}. A perturbative 2-loop conversion
yields B_K^{MSbar-NDR}(2GeV)=0.564(6)_{stat}(3)_{sys}(6)_{PT}, which is in good
agreement with current results from fits to experimental data.Comment: 10 pages, 7 figures. v2: Added one reference and one figure, replaced
2 figures for better readability and updated ensembles, conclusions
unchanged. Final, published versio
High-precision scale setting in lattice QCD
Scale setting is of central importance in lattice QCD. It is required to
predict dimensional quantities in physical units. Moreover, it determines the
relative lattice spacings of computations performed at different values of the
bare coupling, and this is needed for extrapolating results into the continuum.
Thus, we calculate a new quantity, , for setting the scale in lattice QCD,
which is based on the Wilson flow like the scale (M. Luscher, JHEP 1008
(2010) 071). It is cheap and straightforward to implement and compute. In
particular, it does not involve the delicate fitting of correlation functions
at asymptotic times. It typically can be determined on the few per-mil level.
We compute its continuum extrapolated value in 2+1-flavor QCD for physical and
non-physical pion and kaon masses, to allow for mass-independent scale setting
even away from the physical mass point. We demonstrate its robustness by
computing it with two very different actions (one of them with staggered, the
other with Wilson fermions) and by showing that the results agree for physical
quark masses in the continuum limit.Comment: 15 pages, 7 figures, 2 tables; Version published in JHE
Electromagnetic corrections to light hadron masses
At the precision reached in current lattice QCD calculations, electromagnetic
effects are becoming numerically relevant. We will present preliminary results
for electromagnetic corrections to light hadron masses, based on simulations in
which a degree of freedom is superimposed on QCD
configurations from the BMW collaboration.Comment: 7 pages, 2 figures, The XXVIII International Symposium on Lattice
Field Theory, June 14-19,2010, Villasimius, Sardinia Ital
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