263 research outputs found
Equation of State for physical quark masses
We calculate the QCD equation of state for temperatures corresponding to the
transition region with physical mass values for two degenerate light quark
flavors and a strange quark using an improved staggered fermion action
(p4-action) on lattices with temporal extent N_tau=8. We compare our results
with previous calculations performed at twice larger values of the light quark
masses as well as with results obtained from a resonance gas model calculation.
We also discuss the deconfining and chiral aspects of the QCD transition in
terms of renormalized Polyakov loop, strangeness fluctuations and subtracted
chiral condensate. We show that compared to the calculations performed at twice
larger value of the light quark mass the transition region shifts by about 5
MeV toward smaller temperaturesComment: 7 pages, LaTeX, 6 figures; minor corrections, typos corrected,
references adde
Towards Research Collaboration – a Taxonomy of Social Research Network Sites
The increase of scientific collaboration coincides with the technological and social advancement of social software applications which can change the way we research. Among social software, social network sites have recently gained immense popularity in a hedonic context. This paper focuses on social network sites as an emerging application designed for the specific needs of researchers. To give an overview about these sites we use a data set of 24 case studies and in-depth interviews with the founders of ten social research network sites. The gathered data leads to a first tentative taxonomy and to a definition of SRNS identifying four basic functionalities identity and network management, communication, information management, and collaboration. The sites in the sample correspond to one of the following four types: research directory sites, research awareness sites, research management sites and research collaboration sites. These results conclude with implications for providers of social research network sites
Conserved Charge Fluctuations from Lattice QCD and the Beam Energy Scan
We discuss the next-to-leading order Taylor expansion of ratios of cumulants
of net-baryon number fluctuations. We focus on the relation between the
skewness ratio, , and the kurtosis ratio,
. We show that differences in these two
cumulant ratios are small for small values of the baryon chemical potential.
The next-to-leading order correction to however is
approximately three times larger than that for . The former thus
drops much more rapidly with increasing beam energy, . We argue
that these generic patterns are consistent with current data on cumulants of
net-proton number fluctuations measured by the STAR Collaboration at
~GeV.Comment: 4 pages, 4 figures, contribution to the Quark Matter 2015 proceeding
The Spatial String Tension and Dimensional Reduction in QCD
We calculate the spatial string tension in (2+1) flavor QCD with physical
strange quark mass and almost physical light quark masses using lattices with
temporal extent N_tau=4,6 and 8. We compare our results on the spatial string
tension with predictions of dimensionally reduced QCD. This suggests that also
in the presence of light dynamical quarks dimensional reduction works well down
to temperatures 1.5T_c.Comment: 8 pages ReVTeX, 4 figure
Study of the finite temperature transition in 3-flavor QCD using the R and RHMC algorithms
We study the finite temperature transition in QCD with three flavors of equal
masses using the R and RHMC algorithm on lattices with temporal extent
N_{\tau}=4 and 6. For the transition temperature in the continuum limit we find
r_0 T_c=0.429(8) for the light pseudo-scalar mass corresponding to the end
point of the 1st order transition region. When comparing the results obtained
with the R and RHMC algorithms for p4fat3 action we see no significant
step-size errors down to a lightest pseudo-scalar mass of m_{ps} r_0=0.4.Comment: 13 pages, RevTeX, 10 figure
The QCD Equation of State with almost Physical Quark Masses
We present results on the equation of state in QCD with two light quark
flavors and a heavier strange quark. Calculations with improved staggered
fermions have been performed on lattices with temporal extent Nt =4 and 6 on a
line of constant physics with almost physical quark mass values; the pion mass
is about 220 MeV, and the strange quark mass is adjusted to its physical value.
High statistics results on large lattices are obtained for bulk thermodynamic
observables, i.e. pressure, energy and entropy density, at vanishing quark
chemical potential for a wide range of temperatures, 140 MeV < T < 800 MeV. We
present a detailed discussion of finite cut-off effects which become
particularly significant for temperatures larger than about twice the
transition temperature. At these high temperatures we also performed
calculations of the trace anomaly on lattices with temporal extent Nt=8.
Furthermore, we have performed an extensive analysis of zero temperature
observables including the light and strange quark condensates and the static
quark potential at zero temperature. These are used to set the temperature
scale for thermodynamic observables and to calculate renormalized observables
that are sensitive to deconfinement and chiral symmetry restoration and become
order parameters in the infinite and zero quark mass limits, respectively.Comment: 22 pages, 17 EPS-figures; revised version, updated references, data
added in Tab.1, several smaller change
Equation of state and QCD transition at finite temperature
We calculate the equation of state in 2+1 flavor QCD at finite temperature
with physical strange quark mass and almost physical light quark masses using
lattices with temporal extent Nt=8. Calculations have been performed with two
different improved staggered fermion actions, the asqtad and p4 actions.
Overall, we find good agreement between results obtained with these two O(a^2)
improved staggered fermion discretization schemes. A comparison with earlier
calculations on coarser lattices is performed to quantify systematic errors in
current studies of the equation of state. We also present results for
observables that are sensitive to deconfining and chiral aspects of the QCD
transition on Nt=6 and 8 lattices. We find that deconfinement and chiral
symmetry restoration happen in the same narrow temperature interval. In an
Appendix we present a simple parametrization of the equation of state that can
easily be used in hydrodynamic model calculations. In this parametrization we
also incorporated an estimate of current uncertainties in the lattice
calculations which arise from cutoff and quark mass effects. We estimate these
systematic effects to be about 10 MeVComment: 31 pages, 24 EPS-figure
Fluctuations and Correlations of net baryon number, electric charge, and strangeness: A comparison of lattice QCD results with the hadron resonance gas model
We calculate the quadratic fluctuations of net baryon number, electric charge
and strangeness as well as correlations among these conserved charges in
(2+1)-flavor lattice QCD at zero chemical potential. Results are obtained using
calculations with tree level improved gauge and the highly improved staggered
quark (HISQ) actions with almost physical light and strange quark masses at
three different values of the lattice cut-off. Our choice of parameters
corresponds to a value of 160 MeV for the lightest pseudo scalar Goldstone mass
and a physical value of the kaon mass. The three diagonal charge
susceptibilities and the correlations among conserved charges have been
extrapolated to the continuum limit in the temperature interval 150 MeV <T <
250 MeV. We compare our results with the hadron resonance gas (HRG) model
calculations and find agreement with HRG model results only for temperatures
T<= 150 MeV. We observe significant deviations in the temperature range 160 MeV
< T < 170 MeV and qualitative differences in the behavior of the three
conserved charge sectors. At T < 160 MeV quadratic net baryon number
fluctuations in QCD agree with HRG model calculations while, the net electric
charge fluctuations in QCD are about 10% smaller and net strangeness
fluctuations are about 20% larger. These findings are relevant to the
discussion of freeze-out conditions in relativistic heavy ion collisions.Comment: 17 pages, 18 EPS-files, 5 tables, revised version includes continuum
limit extrapolations of off-diagonal susceptibilities, to appear in Phys.
Rev.
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