282 research outputs found
A scalable PC-based parallel computer for lattice QCD
A PC-based parallel computer for medium/large scale lattice QCD simulations
is suggested. The Eotvos Univ., Inst. Theor. Phys. cluster consists of 137
Intel P4-1.7GHz nodes. Gigabit Ethernet cards are used for nearest neighbor
communication in a two-dimensional mesh. The sustained performance for
dynamical staggered(wilson) quarks on large lattices is around 70(110) GFlops.
The exceptional price/performance ratio is below $1/Mflop.Comment: 3 pages, 2 figures, Lattice2002(machines
Critical point of QCD at finite T and \mu, lattice results for physical quark masses
A critical point (E) is expected in QCD on the temperature (T) versus
baryonic chemical potential (\mu) plane. Using a recently proposed lattice
method for \mu \neq 0 we study dynamical QCD with n_f=2+1 staggered quarks of
physical masses on L_t=4 lattices. Our result for the critical point is T_E=162
\pm 2 MeV and \mu_E= 360 \pm 40 MeV. For the critical temperature at \mu=0 we
obtained T_c=164 \pm 2 MeV. This work extends our previous study [Z. Fodor and
S.D.Katz, JHEP 0203 (2002) 014] by two means. It decreases the light quark
masses (m_{u,d}) by a factor of three down to their physical values.
Furthermore, in order to approach the thermodynamical limit we increase our
largest volume by a factor of three. As expected, decreasing m_{u,d} decreased
\mu_E. Note, that the continuum extrapolation is still missingComment: 10 pages, 2 figure
The PMS project: Poor Man's Supercomputer
We briefly describe the Poor Man's Supercomputer (PMS) project carried out at
Eotvos University, Budapest. The goal was to develop a cost effective,
scalable, fast parallel computer to perform numerical calculations of physical
problems that can be implemented on a lattice with nearest neighbour
interactions. To this end we developed the PMS architecture using PC components
and designed a special, low cost communication hardware and the driver software
for Linux OS. Our first implementation of PMS includes 32 nodes (PMS1). The
performance of PMS1 was tested by Lattice Gauge Theory simulations. Using SU(3)
pure gauge theory or bosonic MSSM on PMS1 we obtained 3Mflop
price-to-sustained performance for double and single precision operations,
respectively. The design of the special hardware and the communication driver
are freely available upon request for non-profit organizations.Comment: Latex, 13 pages, 6 figures included, minor additions, typos correcte
The QCD transition temperature: results with physical masses in the continuum limit
The transition temperature () of QCD is determined by Symanzik improved
gauge and stout-link improved staggered fermionic lattice simulations. We use
physical masses both for the light quarks () and for the strange quark
(). Four sets of lattice spacings (=4,6,8 and 10) were used to carry
out a continuum extrapolation. It turned out that only =6,8 and 10 can be
used for a controlled extrapolation, =4 is out of the scaling region.
Since the QCD transition is a non-singular cross-over there is no unique .
Thus, different observables lead to different numerical values even in
the continuum and thermodynamic limit. The peak of the renormalized chiral
susceptibility predicts =151(3)(3) MeV, wheres -s based on the
strange quark number susceptibility and Polyakov loops result in 24(4) MeV and
25(4) MeV larger values, respectively. Another consequence of the cross-over is
the non-vanishing width of the peaks even in the thermodynamic limit, which we
also determine. These numbers are attempted to be the full result for the
0 transition, though other lattice fermion formulations (e.g. Wilson)
are needed to cross-check them.Comment: 13 pages 5 figures. Final version, published in Phys.Lett.
Enigma of ultraluminous X-ray sources may be resolved by 3D-spectroscopy (MPFS data)
The ultraluminous X-ray sources (ULXs) were isolated in external galaxies for
the last 5 years. Their X-ray luminosities exceed 100-10000 times those of
brightest Milky Way black hole binaries and they are extremely variable. There
are two models for the ULXs, the best black hole candidates. 1. They are
supercritical accretion disks around a stellar mass black hole like that in
SS433, observed close to the disk axes. 2. They are Intermediate Mass Black
Holes (of 100-10000 solar masses). Critical observations which may throw light
upon the ULXs nature come from observations of nebulae around the ULXs. We
present results of 3D-spectroscopy of nebulae around several ULXs located in
galaxies at 3-6 Mpc distances. We found that the nebulae to be powered by their
central black holes. The nebulae are shocked and dynamically perturbed probably
by jets. The nebulae are compared with SS433 nebula (W50).Comment: Proceedings of the ESO and Euro3D Workshop "Science Perspectives for
3D Spectroscopy", Garching (Germany), October 10-14, 2005. M. Kissler-Patig,
M.M. Roth and J.R. Walsh (eds.
Dynamical overlap fermions, results with hybrid Monte-Carlo algorithm
We present first, exploratory results of a hybrid Monte-Carlo algorithm for
dynamical, n_f=2, four-dimensional QCD with overlap fermions. As expected, the
computational requirements are typically two orders of magnitude larger for the
dynamical overlap formalism than for the more conventional (Wilson or
staggered) formulations.Comment: 13 pages, 2 figure
The QCD equation of state at nonzero densities: lattice result
In this letter we give the equation of state of QCD at finite temperatures
and densities. The recently proposed overlap improving multi-parameter
reweighting technique is used to determine observables at nonvanishing chemical
potentials. Our results are obtained by studying n_f=2+1 dynamical staggered
quarks with semi-realistic masses on N_t=4 lattices.Comment: 5 pages, 6 figure
A new method to study lattice QCD at finite temperature and chemical potential
Due to the sign problem, it is exponentially difficult to study QCD on the
lattice at finite chemical potential. We propose a method --an overlap
improving multi-parameter reweighting technique-- to alleviate this problem. We
apply this method and give the phase diagram of four-flavor QCD obtained on
lattices 4^4 and 4\cdot6^3. Our results are based on {\cal{O}}(10^3-10^4)
configurations.Comment: minor changes, version to appear in Phys. Lett.
Grand canonical potential for a static quark--anti-quark pair at finite T/mu
We present numerical results on the static quark--anti-quark grand canonical
potential in full QCD at non-vanishing temperature () and quark chemical
potential (). Non-zero -s are reached by means of multi-parameter
reweighting. The dynamical staggered simulations were carried out for
flavors with physical quark masses on lattices.Comment: Lattice2004(non-zero
Structure of Fat Jets at the Tevatron and Beyond
Boosted resonances is a highly probable and enthusiastic scenario in any
process probing the electroweak scale. Such objects when decaying into jets can
easily blend with the cornucopia of jets from hard relative light QCD states.
We review jet observables and algorithms that can contribute to the
identification of highly boosted heavy jets and the possible searches that can
make use of such substructure information. We also review previous studies by
CDF on boosted jets and its measurements on specific jet shapes.Comment: invited review for a special "Top and flavour physics in the LHC era"
issue of The European Physical Journal C, we invite comments regarding
contents of the review; v2 added references and institutional preprint
number
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