50 research outputs found
Static pair free energy and screening masses from correlators of Polyakov loops: continuum extrapolated lattice results at the QCD physical point
We study the correlators of Polyakov loops, and the corresponding gauge
invariant free energy of a static quark-antiquark pair in 2+1 flavor QCD at
finite temperature. Our simulations were carried out on = 6, 8, 10, 12,
16 lattices using Symanzik improved gauge action and a stout improved staggered
action with physical quark masses. The free energies calculated from the
Polyakov loop correlators are extrapolated to the continuum limit. For the free
energies we use a two step renormalization procedure that only uses data at
finite temperature. We also measure correlators with definite Euclidean time
reversal and charge conjugation symmetry to extract two different screening
masses, one in the magnetic, and one in the electric sector, to distinguish two
different correlation lengths in the full Polyakov loop correlator
QCD finite T transition -- Comparison between Wilson and staggered results
A quantitative comparison between the finite temperature behaviour of the
staggered and Wilson fermion formulations are performed. The comparison is
based on a physical quantity that is expected to be quite sensitive to the
fermionic features of the action. For that purpose we use the height of the
peak for , where is the quark number susceptibility.Comment: 6 pages. Talk presented at Lattice 200
Curvature of the phase transition line in the mu-T plane
We determined the curvature of the phase transition line in the mu-T plane
using a Taylor expansion in mu. The Polyakov loop and the strange quark number
susceptibility were measured to locate the pseudocritical line. The analysis
was carried out on Nt=4,6,8,10 lattices generated with a Symanzik improved
gauge and stout-link improved (2+1) flavour staggered fermion action using
physical quark masses.Comment: 7 pages, 5 figures; format adjuste
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
Spectral functions of charmonium with 2+1 flavours of dynamical quarks
Finite temperature charmonium spectral functions in the pseudoscalar(PS) and
vector(V) channels are studied in lattice QCD with 2+1 flavours of dynamical
Wilson quarks, on fine isotropic lattices (with a lattice spacing of 0.057fm),
with a non-physical pion mass of 545MeV. The highest temperature studied is
approximately 1.4Tc. Up to this temperature no significant variation of the
spectral function is seen in the PS channel. The V channel shows some
temperature dependence, which seems to be consistent with a temperature
dependent low frequency peak related to heavy quark transport, plus a
temperature independent term at omega > 0. These results are in accord with
previous calculations using the quenched approximation.Comment: Conference proceedings: The 32nd International Symposium on Lattice
Field Theory - Lattice 2014 June 23-28, 2014 Columbia University, New York,
New York This conference contribution draws heavily from the paper:
arXiv:1401.5940 [hep-lat
Better than $1/Mflops sustained: a scalable PC-based parallel computer for lattice QCD
We study the feasibility of a PC-based parallel computer for medium to large
scale lattice QCD simulations. The E\"otv\"os Univ., Inst. Theor. Phys. cluster
consists of 137 Intel P4-1.7GHz nodes with 512 MB RDRAM. The 32-bit, single
precision sustained performance for dynamical QCD without communication is 1510
Mflops/node with Wilson and 970 Mflops/node with staggered fermions. This gives
a total performance of 208 Gflops for Wilson and 133 Gflops for staggered QCD,
respectively (for 64-bit applications the performance is approximately halved).
The novel feature of our system is its communication architecture. In order to
have a scalable, cost-effective machine we use Gigabit Ethernet cards for
nearest-neighbor communications in a two-dimensional mesh. This type of
communication is cost effective (only 30% of the hardware costs is spent on the
communication). According to our benchmark measurements this type of
communication results in around 40% communication time fraction for lattices
upto 48^3\cdot96 in full QCD simulations. The price/sustained-performance ratio
for full QCD is better than 1.5/Mflops for
staggered) quarks for practically any lattice size, which can fit in our
parallel computer. The communication software is freely available upon request
for non-profit organizations.Comment: 14 pages, 3 figures, final version to appear in Comp.Phys.Com
Spectral functions of charmonium with 2+1 flavours of dynamical quarks
Finite temperature charmonium spectral functions in the
pseudoscalar(PS) and vector(V) channels are studied in lattice
QCD with 2+1 flavours of dynamical Wilson quarks, on fine
isotropic lattices (with a lattice spacing of 0.057fm), with a
non-physical pion mass of 545MeV. The highest temperature
studied is approximately 1.4Tc. Up to this temperature no
significant variation of the spectral function is seen in the PS
channel. The V channel shows some temperature dependence, which
seems to be consistent with a temperature dependent low
frequency peak related to heavy quark transport, plus a
temperature independent term at omega > 0. These results are in
accord with previous calculations using the quenched
approximation
Fluctuations of conserved charges at finite temperature from lattice QCD
We present the full results of the Wuppertal-Budapest lattice QCD
collaboration on flavor diagonal and non-diagonal quark number susceptibilities
with 2+1 staggered quark flavors, in a temperature range between 125 and 400
MeV. The light and strange quark masses are set to their physical values.
Lattices with Nt=6, 8, 10, 12, 16 are used. We perform a continuum
extrapolation of all observables under study. A Symanzik improved gauge and a
stout-link improved staggered fermion action is utilized. All results are
compared to the Hadron Resonance Gas model predictions: good agreement is found
in the temperature region below the transition.Comment: 13 pages, 8 figures in Jhep styl
Is there still any Tc mystery in lattice QCD? Results with physical masses in the continuum limit III
The present paper concludes 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 (=16) and we work
again with physical quark masses. The new results on this broad cross-over are
in complete agreement with our earlier ones. We compare our findings 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 in these analytic calculations. The
findings of the hotQCD collaboration can be recovered by using a distorted
spectrum which takes into account lattice discretization artifacts and heavier
than physical quark masses. This analysis provides a simple explanation for the
observed discrepancy in the transition temperatures between our and the hotQCD
collaborations.Comment: 25 pages, 10 figures and 3 table