1,668 research outputs found
Wilson Loop in Classical Lattice Gauge Theory and the Thermal Width of Heavy Quarkonium
We present an estimate for the imaginary part of the recently introduced
finite temperature real-time static potential. It can be extracted from the
time evolution of the Wilson loop in classical lattice gauge theory. The
real-time static potential determines, through a Schroedinger-type equation and
a subsequent Fourier-transform of its solution, the spectral function of heavy
quarkonium in finite-temperature QCD. We also compare the results of the
classical simulations with those of Hard Thermal Loop improved simulations, as
well as with analytic expectations based on resummed perturbation theory.Comment: 7 pages, 3 figures, XXV International Symposium on Lattice Field
Theor
The non-perturbative QCD Debye mass from a Wilson line operator
According to a proposal by Arnold and Yaffe, the non-perturbative
g^2T-contribution to the Debye mass in the deconfined QCD plasma phase can be
determined from a single Wilson line operator in the three-dimensional pure
SU(3) gauge theory. We extend a previous SU(2) measurement of this quantity to
the physical SU(3) case. We find a numerical coefficient which is more accurate
and smaller than that obtained previously with another method, but still very
large compared with the naive expectation: the correction is larger than the
leading term up to T ~ 10^7 T_c, corresponding to g^2 ~ 0.4. At moderate
temperatures T ~ 2 T_c, a consistent picture emerges where the Debye mass is
m_D ~ 6T, the lightest gauge invariant screening mass in the system is ~ 3T,
and the purely magnetic operators couple dominantly to a scale ~ 6T. Electric
(~ gT) and magnetic (~ g^2T) scales are therefore strongly overlapping close to
the phase transition, and the colour-electric fields play an essential role in
the dynamics.Comment: 10 pages; typos corrected, to appear in Phys.Lett.
Lattice constraints on the thermal photon rate
We estimate the photon production rate from an SU(3) plasma at temperatures
of about 1.1Tc and 1.3Tc. Lattice results for the vector current correlator at
spatial momenta k ~ (2-6)T are extrapolated to the continuum limit and analyzed
with the help of a polynomial interpolation for the corresponding spectral
function, which vanishes at zero frequency and matches to high-precision
perturbative results at large invariant masses. For small invariant masses the
interpolation is compared with the NLO weak-coupling result, hydrodynamics, and
a holographic model. At vanishing invariant mass we extract the photon rate
which for k \gsim 3T is found to be close to the NLO weak-coupling prediction.
For k \lsim 2T uncertainties remain large but the photon rate is likely to fall
below the NLO prediction, in accordance with the onset of a strongly
interacting behaviour characteristic of the hydrodynamic regime.Comment: 20 pages. v2: clarifications adde
A non-perturbative estimate of the heavy quark momentum diffusion coefficient
We estimate the momentum diffusion coefficient of a heavy quark within a pure
SU(3) plasma at a temperature of about 1.5Tc. Large-scale Monte Carlo
simulations on a series of lattices extending up to 192^3*48 permit us to carry
out a continuum extrapolation of the so-called colour-electric imaginary-time
correlator. The extrapolated correlator is analyzed with the help of
theoretically motivated models for the corresponding spectral function.
Evidence for a non-zero transport coefficient is found and, incorporating
systematic uncertainties reflecting model assumptions, we obtain kappa = (1.8 -
3.4)T^3. This implies that the "drag coefficient", characterizing the time
scale at which heavy quarks adjust to hydrodynamic flow, is (1.8 - 3.4)
(Tc/T)^2 (M/1.5GeV) fm/c, where M is the heavy quark kinetic mass. The results
apply to bottom and, with somewhat larger systematic uncertainties, to charm
quarks.Comment: 18 pages. v2: clarifications adde
Critical point and scale setting in SU(3) plasma: An update
We explore a method developed in statistical physics which has been argued to
have exponentially small finite-volume effects, in order to determine the
critical temperature Tc of pure SU(3) gauge theory close to the continuum
limit. The method allows us to estimate the critical coupling betac of the
Wilson action for temporal extents up to Nt ~ 20 with < 0.1% uncertainties.
Making use of the scale setting parameters r0 and sqrt{t0} in the same range of
beta-values, these results lead to the independent continuum extrapolations Tc
r0 = 0.7457(45) and Tc sqrt{t0} = 0.2489(14), with the latter originating from
a more convincing fit. Inserting a conversion of r0 from literature
(unfortunately with much larger errors) yields Tc / LambdaMSbar = 1.24(10).Comment: 12 pages. v2: clarifications and references added, published versio
Heavy Quark Interactions and Quarkonium Binding
We consider heavy quark interactions in quenched and unquenched lattice QCD.
In a region just above the deconfinement point, non-Abelian gluon polarization
leads to a strong increase in the binding. Comparing quark-antiquark and
quark-quark interaction, the dependence of the binding on the separation
distance is found to be the same for the colorless singlet and
the colored anti-triplet state. In a potential model description of
in-medium behavior, this enhancement of the binding leads to a
survival up to temperatures of 1.5 or higher; it could also result in
flow.Comment: 8 pages, 8 Figures; invited talk at "Strangeness in Quark Matter
2008", Beijing/China, to appear in the Proceeding
Towards the continuum limit in transport coefficient computations
The analytic continuation needed for the extraction of transport coefficients
necessitates in principle a continuous function of the Euclidean time variable.
We report on progress towards achieving the continuum limit for 2-point
correlator measurements in thermal SU(3) gauge theory, with specific attention
paid to scale setting. In particular, we improve upon the determination of the
critical lattice coupling and the critical temperature of pure SU(3) gauge
theory, estimating r0*Tc ~ 0.7470(7) after a continuum extrapolation. As an
application the determination of the heavy quark momentum diffusion coefficient
from a correlator of colour-electric fields attached to a Polyakov loop is
discussed.Comment: 7 pages. To appear in the Proceedings of the 31st International
Symposium on Lattice Field Theory, July 29 - August 3, 2013, Mainz, German
Heavy quark medium polarization at next-to-leading order
We compute the imaginary part of the heavy quark contribution to the photon
polarization tensor, i.e. the quarkonium spectral function in the vector
channel, at next-to-leading order in thermal QCD. Matching our result, which is
valid sufficiently far away from the two-quark threshold, with a previously
determined resummed expression, which is valid close to the threshold, we
obtain a phenomenological estimate for the spectral function valid for all
non-zero energies. In particular, the new expression allows to fix the overall
normalization of the previous resummed one. Our result may be helpful for
lattice reconstructions of the spectral function (near the continuum limit),
which necessitate its high energy behaviour as input, and can in principle also
be compared with the dilepton production rate measured in heavy ion collision
experiments. In an appendix analogous results are given for the scalar channel.Comment: 43 pages. v2: a figure and other clarifications added, published
versio
The spectrum of the three-dimensional adjoint Higgs model and hot SU(2) gauge theory
We compute the mass spectrum of the SU(2) adjoint Higgs model in 2+1
dimensions at several points located in the (metastable) confinement region of
its phase diagram. We find a dense spectrum consisting of an almost unaltered
repetition of the glueball spectrum of the pure gauge theory, and additional
bound states of adjoint scalars. For the parameters chosen, the model
represents the effective finite temperature theory for pure SU(2) gauge theory
in four dimensions, obtained after perturbative dimensional reduction.
Comparing with the spectrum of screening masses obtained in recent simulations
of four-dimensional pure gauge theory at finite temperature, for the low lying
states we find quantitative agreement between the full and the effective theory
for temperatures as low as T = 2 Tc. This establishes the model under study as
the correct effective theory, and dimensional reduction as a viable tool for
the description of thermodynamic properties. We furthermore compare the
perturbative contribution O(g.T) with the non-perturbative contributions
O(g^2.T) and O(g^3.T) to the Debye mass. The latter turns out to be dominated
by the scale g^2.T, whereas higher order contributions are small corrections.Comment: LaTeX. Typos corrected and references adde
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