2,307 research outputs found
Screening of heavy quark free energies at finite temperature and non-zero baryon chemical potential
We analyze the dependence of heavy quark free energies on the baryon chemical
potential (mu_b) in 2-flavour QCD using improved (p4) staggered fermions with a
bare quark mass of m/T = 0.4. By performing a 6th order Taylor expansion in the
chemical potential which circumvents the sign problem. The Taylor expansion
coefficients of colour singlet and colour averaged free energies are calculated
and from this the expansion coefficients for the corresponding screening masses
are determined. We find that for small mu_b the free energies of a static quark
anti-quark pair decrease in a medium with a net excess of quarks and that
screening is well described by a screening mass which increases with increasing
mu_b. The mu_b-dependent corrections to the screening masses are well described
by perturbation theory for T > 2 T_c. In particular, we find for all
temperatures above T_c that the expansion coefficients for singlet and colour
averaged screening masses differ by a factor 2.Comment: 14 page
Modes of clustered star formation
The realization that most stars form in clusters, raises the question of
whether star/planet formation are influenced by the cluster environment. The
stellar density in the most prevalent clusters is the key factor here. Whether
dominant modes of clustered star formation exist is a fundamental question.
Using near-neighbour searches in young clusters Bressert et al. (2010) claim
this not to be the case and conclude that star formation is continuous from
isolated to densely clustered. We investigate under which conditions
near-neighbour searches can distinguish between different modes of clustered
star formation. Near-neighbour searches are performed for model star clusters
investigating the influence of the combination of different cluster modes,
observational biases, and types of diagnostic and find that the cluster density
profile, the relative sample sizes, limitations in observations and the choice
of diagnostic method decides whether modelled modes of clustered star formation
are detected. For centrally concentrated density distributions spanning a wide
density range (King profiles) separate cluster modes are only detectable if the
mean density of the individual clusters differs by at least a factor of ~65.
Introducing a central cut-off can lead to underestimating the mean density by
more than a factor of ten. The environmental effect on star and planet
formation is underestimated for half of the population in dense systems. A
analysis of a sample of cluster environments involves effects of superposition
that suppress characteristic features and promotes erroneous conclusions. While
multiple peaks in the distribution of the local surface density imply the
existence of different modes, the reverse conclusion is not possible. Equally,
a smooth distribution is not a proof of continuous star formation, because such
a shape can easily hide modes of clustered star formation (abridged)Comment: 9 pages, 6 figures, accepted by A&
Heavy Quark Interactions in Finite Temperature QCD
We study the free energy of a heavy quark-antiquark pair in a thermal medium.
We constuct a simple ansatz for the free energy for two quark flavors motivated
by the Debye-H\"uckel theory of screening.Comment: 4 pages, 4 figures, contribution to the proceedings of the
International Conference on Hard and Electromagnetic Probes of High Energy
Nuclear Collisions, Ericeira, Portugal, Nov. 4-10, 200
Heavy quark free energies and screening at finite temperature and density
We study the free energies of heavy quarks calculated from Polyakov loop
correlation functions in full 2-flavour QCD using the p4-improved staggered
fermion action. A small but finite Baryon number density is included via Taylor
expansion of the fermion determinant in the Baryo-chemical potential mu. For
temperatures above Tc we extract Debye screening masses from the large distance
behaviour of the free energies and compare their mu-dependence to perturbative
results.Comment: 6 pages, Presented at 23rd International Symposium on Lattice Field
Theory (Lattice 2005), Trinity College, Dublin, Ireland, 25-30 Jul 200
Determination of Freeze-out Conditions from Lattice QCD Calculations
Freeze-out conditions in Heavy Ion Collisions are generally determined by
comparing experimental results for ratios of particle yields with theoretical
predictions based on applications of the Hadron Resonance Gas model. We discuss
here how this model dependent determination of freeze-out parameters may
eventually be replaced by theoretical predictions based on equilibrium QCD
thermodynamics.Comment: presented at the International Conference "Critical Point and Onset
of Deconfinement - CPOD 2011", Wuhan, November 7-11, 201
Numerical study of the equation of state for two flavor QCD at finite density
We discuss the equation of state for 2 flavor QCD at non-zero temperature and
density. Derivatives of with respect to quark chemical potential
up to fourth order are calculated, enabling estimates of the pressure,
quark number density and associated susceptibilities as functions of
via a Taylor series expansion. It is found that the fluctuations in the quark
number density increase in the vicinity of the phase transition temperature and
the susceptibilities start to develop a pronounced peak as is
increased. This suggests the presence of a critical endpoint in the plane.Comment: 5 pages, 4 figures, Talk at Confinement 200
COSMIC: US-based Conversion Master\u27s Degree in Computing
COSMIC is an NSF S-STEM graduate curriculum initiative/conversion program that strives to provide an accelerated pathway to a Master of Science (MS) degree for individuals who do not have an undergraduate degree in computing, but who wish to cross over into the computing field. The structure of our conversion program, the context that motivated it, and insights from conversion students\u27 instructors are presented. Program successes with students from under-represented populations and the limitations that are also experienced are discussed. Our conversion program is based on a highly focused summer bridge course, combined with a customized curriculum pathway that enables people without undergraduate computing degrees to merge quickly and efficiently into a professional MS in computing degree program. The program is similar in concept to post-baccalaureate conversion programs in New Zealand (e.g., the Master of Software Development at the Victoria University of Wellington) and the extensive conversion choices in the UK. Undergraduate and graduate student enrollment statistics from past and current (2018) CRA Taulbee Surveys strongly suggest the computing profession has a moral obligation to seek out and encourage individuals from under-represented populations to become a significant part of the computing professional community. We encourage other institutions to join in the effort to recruit and provide pathways for post-baccalaureate individuals from under-represented populations to become a significant part of the computing community
Lattice calculation of medium effects at short and long distances
We investigate medium effects in QCD like chromoelectric screening and
quasi-particle mass generation by calculating the heavy quark potential as well
as the temporal quark and gluon Coulomb gauge propagators in quenched
approximation.Comment: To appear in proceedings of Quark Matter 2001, 4 pages LaTeX, uses
espcrc1.st
QCD at non-zero chemical potential and temperature from the lattice
A study of QCD at non-zero chemical potential, mu, and temperature, T, is
performed using the lattice technique. The transition temperature (between the
confined and deconfined phases) is determined as a function of mu and is found
to be in agreement with other work. In addition the variation of the pressure
and energy density with mu is obtained for small positive mu. These results are
of particular relevance for heavy-ion collision experiments.Comment: Invited paper presented at the Joint Workshop on Physics at the
Japanese Hadron Facility, March 2002, Adelaide. 10 pages, uses
ws-procs9x6.cls style file (provided
The QCD equation of state for two flavours at non-zero chemical potential
We present results of a simulation of 2 flavour QCD on a
lattice using p4-improved staggered fermions with bare quark mass .
Derivatives of the thermodynamic grand canonical partition function
with respect to chemical potentials for
different quark flavours are calculated up to sixth order, enabling estimates
of the pressure and the quark number density as well as the chiral condensate
and various susceptibilities as functions of via Taylor series
expansion. Results are compared to high temperature perturbation theory as well
as a hadron resonance gas model. We also analyze baryon as well as isospin
fluctuations and discuss the relation to the chiral critical point in the QCD
phase diagram. We moreover discuss the dependence of the heavy quark free
energy on the chemical potential.Comment: 4 pages, 7 figures, talk presented at Quark Matter 2005, Budapes
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