1,874 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
The Problem of Mass: Mesonic Bound States Above T_c
We discuss the problem of mass, noting that meson masses decrease with
increasing scale as the dynamically generated condensate of "soft glue" is
melted (Brown/Rho scaling). We then extend the Bielefeld LGS color singlet
interaction computed for heavy quarks in a model-dependent way by including the
Ampere law velocity-velocity interaction. Parameterizing the resulting
interaction in terms of effective strength of the potential and including
screening, we find that the masses of pi, sigma, rho and A1 excitations, 32
degrees of freedom in all, go to zero (in the chiral limit) as T goes to Tc
essentially independently of the input quark (thermal) masses in the range of
1-2 GeV, calculated also in Bielefeld. We discuss other LGS which show q-bar q
bound states, which we interpret as our chirally restored mesons, for T > Tc.Comment: 20 pages, 6 figures (Table 2 is added
Heavy quark potential and quarkonia dissociation rates
Quenched lattice data for the quark-antiquark interaction (in terms of heavy
quark free energies) in the color singlet channel at finite temperatures are
fitted and used within the nonrelativistic Schroedinger equation formalism to
obtain binding energies and scattering phase shifts for the lowest eigenstates
in the charmonium and bottomonium systems in a hot gluon plasma. The partial
dissociation rate due to the Bhanot-Peskin process is calculated using
different assumptions for the gluon distribution function, including free
massless gluons, massive gluons, and massive damped gluons. It is demonstrated
that a temperature dependent gluon mass has an essential influence on the heavy
quarkonia dissociation, but that this process alone is insufficient to describe
the heavy quarkonia dissociation rates.Comment: 4 pages, 5 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
Dimension 2 condensates and Polyakov Chiral Quark Models
We address a possible relation between the expectation value of the Polyakov
loop in pure gluodynamics and full QCD based on Polyakov Chiral Quark Models
where constituent quarks and the Polyakov loop are coupled in a minimal way. To
this end we use a center symmetry breaking Gaussian model for the Polyakov loop
distribution which accurately reproduces gluodynamics data above the phase
transition in terms of dimension 2 gluon condensate. The role played by the
quantum and local nature of the Polyakov loop is emphasized.Comment: 3 pages, 1 figure. Talk given at the IVth International Conference on
Quarks an Nuclear Physics, Madrid, June 5th-10th 200
Book Review - Energy Futures
Review of Russell Gold, The Boom: How Fracking Ignited the American Energy Revolution and Changed the World (New York: Simon & Schuster, 2014
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
Thermodynamics of two-colour QCD
We discuss the thermodynamics of two-colour QCD with four flavours of
staggered quarks on 8^3x4 and 16^3x4 lattices. In our simulations we use the
Naik action for the fermions and a (1,2) tree-level improved gauge action. We
analyze the deconfinement and chiral phase transitions for four different quark
masses (m=0.1,0.05,0.025,0.015). Contrary to three-colour QCD the peak in the
Polyakov loop susceptibility decreases with decreasing quark mass. This
reflects an early breaking of the string in the heavy quark potential, which we
verify explicitly by calculating the heavy quark potential at finite
temperature using Polyakov loop correlations.Comment: LATTICE98(hightemp), 3 pages, LaTeX2e File, 5 EPS-figures,
espcrc2.st
Matter formed at the BNL relativistic heavy ion collider
We suggest that the "new form of matter" found just above by RHIC is
made up of tightly bound quark-antiquark pairs, essentially 32 chirally
restored (more precisely, nearly massless) mesons of the quantum numbers of
, , and . Taking the results of lattice gauge
simulations (LGS) for the color Coulomb potential from the work of the
Bielefeld group and feeding this into a relativistic two-body code, after
modifying the heavy-quark lattice results so as to include the
velocity-velocity interaction, all ground-state eigenvalues of the 32 mesons go
to zero at just as they do from below as predicted by the vector
manifestation (VM in short) of hidden local symmetry. This could explain the
rapid rise in entropy up to found in LGS calculations. We argue that how
the dynamics work can be understood from the behavior of the hard and soft
glue.Comment: Final versio
String breaking in Lattice QCD
The separation of a heavy quark and antiquark pair leads to the formation of
a tube of flux, or string, which should break in the presence of light
quark-antiquark pairs. This expected zero temperature phenomenon has proven
elusive in simulations of lattice QCD. We present simulation results that show
that the string does break in the confining phase at nonzero temperature.Comment: LATTICE98(hightemp), 3 pages, 4 figures, LaTe
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