37,576 research outputs found
A faster method of computation of lattice quark number susceptibilities
We compute the quark number susceptibilities in two flavor QCD for staggered
fermions by adding the chemical potential as a Lagrange multiplier for the
point-split number density term. Since lesser number of quark propagators are
required at any order, this method leads to faster computations. We propose a
subtraction procedure to remove the inherent undesired lattice terms and check
that it works well by comparing our results with the existing ones where the
elimination of these terms is analytically guaranteed. We also show that the
ratios of susceptibilities are robust, opening a door for better estimates of
location of the QCD critical point through the computation of the tenth and
twelfth order baryon number susceptibilities without significant additional
computational overload.Comment: 10 pages, 12 figure
Screening correlators with chiral Fermions
We study screening correlators of quark-antiquark composites at T=2T_c, where
T_c is the QCD phase transition temperature, using overlap quarks in the
quenched approximation of lattice QCD. As the lattice spacing is changed from
1/4T to a=1/6T and 1/8T, we find that screening correlators change little, in
contrast with the situation for other types of lattice fermions. All
correlators are close to the ideal gas prediction at small separations. The
long distance falloff is clearly exponential, showing that a parametrization by
a single screening length is possible at distances z > 1/T. The correlator
corresponding to the thermal vector is close to the ideal gas value at all
distances, whereas that for the thermal scalar deviates at large distances.
This is examined through the screening lengths and momentum space correlators.
There is strong evidence that the screening transfer matrix does not have
reflection positivity.Comment: 10 pages, 9 fig
Phases and properties of quark matter
I review recent developments in finite temperature lattice QCD which are
useful for the study of heavy-ion collisions. I pay particular attention to
studies of the equation of state and the light they throw on conformal symmetry
and the large N_c limit, and to the structure of the phase diagram for N_f=2+1.Comment: Plenary talk at Quark Matter 2008, Jaipur, India (8 pages, 5 figures
Probing the quark-gluon plasma with a new Fermionic correlator
We present the first measurement of a new correlation function of Fermion bilinears in finite temperature QCD with and without dynamical quarks in a quantum number channel in which non-trivial correlations are known to be present for purely gluonic operators. We find that the Fermion correlator vanishes for , in agreement with the expectation for weakly interacting quarks in a quark-gluon plasma
Valence quarks in the QCD plasma: quark number susceptibilities and screening
We have investigated the quark sector of quenched QCD for 1.5\le T/Tc\le3 in the continuum limit, using two different lattice discretisations of quarks and extrapolating from lattice spacings between 1/4T and 1/14T. At these temperatures, the flavour off-diagonal susceptibility, chi_{ud}/T^2, is compatible with zero at each lattice spacing, and hence also in the continuum limit. In the continuum limit, the light quark susceptibilities are about 10% less than the ideal gas results even at the highest T, in agreement with hard thermal loop predictions but marginally below a resummed perturbative computation. For the mass range appropriate to the strange quark, the flavour diagonal susceptibility is significantly smaller. Our estimate of the Wroblewski parameter is compatible with observations at RHIC and SPS. The continuum limit of screening masses in all (local) quark-bilinears is very close to the ideal gas results
Solving large-scale dynamic systems using band Lanczos method in Rockwell NASTRAN on CRAY X-MP
The improved cost effectiveness using better models, more accurate and faster algorithms and large scale computing offers more representative dynamic analyses. The band Lanczos eigen-solution method was implemented in Rockwell's version of 1984 COSMIC-released NASTRAN finite element structural analysis computer program to effectively solve for structural vibration modes including those of large complex systems exceeding 10,000 degrees of freedom. The Lanczos vectors were re-orthogonalized locally using the Lanczos Method and globally using the modified Gram-Schmidt method for sweeping rigid-body modes and previously generated modes and Lanczos vectors. The truncated band matrix was solved for vibration frequencies and mode shapes using Givens rotations. Numerical examples are included to demonstrate the cost effectiveness and accuracy of the method as implemented in ROCKWELL NASTRAN. The CRAY version is based on RPK's COSMIC/NASTRAN. The band Lanczos method was more reliable and accurate and converged faster than the single vector Lanczos Method. The band Lanczos method was comparable to the subspace iteration method which was a block version of the inverse power method. However, the subspace matrix tended to be fully populated in the case of subspace iteration and not as sparse as a band matrix
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