REVIEW
Static quark anti-quark free energy and the running coupling at finite temperature
High Energy Physics - Lattice · Submitted 23 Jun 2004 · 24 references
Pith's verdict: Real lattice data and a quotable r_screen scaling law; the confinement-remnant headline is a gloss on a gauge-fixed correlator, not a derived result.
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Referee report
The paper
The paper claims
The quark-antiquark force in a hot gluon plasma keeps its zero-temperature strength at short distances and only screens beyond a temperature-set length scale.
The reading
What carries the argument
The load-bearing object is the color-singlet heavy quark free energy $F_1(r,T)$, obtained from the Coulomb-gauge-fixed Polyakov loop correlator $Tr L(x) L^†(0)$ and normalized by matching its short-distance part to the zero-temperature heavy quark potential. Two derived quantities carry the argument: the potential-scheme coupling $α_V = -(3r/4)F_1$, which is sensitive to the sign change that a confining linear term forces, and the force-scheme coupling $α_{qq} = (3r^2/4) dF_1/dr$, which stays positive and whose maximum locates the screening length. A lattice-spacing correction replaces the separation $r$ by $r_I$ defined through the Fourier transform of the tree-level improved gluon propagator, which removes most of the rotational-symmetry breaking at short distances and is what makes the $r < 0.1$ fm comparison with perturbation theory meaningful.
Extended reading notes
Core claim
The authors compute the color-singlet free energy $F_1(r,T)$ of a static quark-antiquark pair in quenched QCD on $32^3 x N_τ$ lattices with $N_τ = 4, 8, 16$ and a tree-level Symanzik-improved gauge action, renormalizing it by matching the short-distance part to the zero-temperature heavy quark potential. From it they build two couplings, $α_V(r,T) = -(3r/4) F_1(r,T)$ and $α_{qq}(r,T) = (3r^2/4) dF_1(r,T)/dr$, and find that for $r <~ 0.1$ fm both agree with the zero-temperature lattice potential and with the two-loop perturbative force, with no visible temperature dependence up to $T ≃ 3T_c$; above that, thermal effects reach even into the short-distance regime. Beyond $r ≃ 0.1$ fm non-perturbative physics takes over: $α_V$ changes sign for $T_c <= T <~ 3T_c$, exactly as a linearly rising confining potential would force it to, while $α_{qq}$ rises and then peaks. The location of that peak defines the screening scale, and across the whole temperature range it obeys $r_{screen} = (0.48 +- 0.01)$ fm $T_c/T$. At large distances the authors fit $F_1$ with a Debye-screened Coulomb form containing two independent couplings, $α(T)$ and $ã(T)$; their ratio approaches one only for $T >~ 6T_c$ and reaches about five near $T_c$, so a temperature-dependent coupling is badly scheme dependent for $T_c <= T <~ 2T_c$. For $T >= 6T_c$ a single rescaled two-loop coupling, $α(T) = 2.095(82) α_{pert}(T)$, describes both the Coulomb strength and the screening mass. The conclusion the authors draw is that the near-$T_c$ plasma is better described by remnants of confinement than by a strong Coulombic force.
Load-bearing premise
The argument depends on the Coulomb-gauge-fixed Polyakov loop correlator being a faithful stand-in for a physical, gauge-invariant singlet free energy at the distances and temperatures studied, since if that identification only approximately holds, the extracted coupling describes a gauge-dependent quantity rather than the plasma.
Editorial extensions
If this is right
- Short-distance observables at separations below about $0.1$ fm in a quark-gluon plasma up to $3T_c$ can be computed with vacuum QCD input, without thermal corrections to the coupling.
- The relation $r_{screen} = (0.48 +- 0.01)$ fm $T_c/T$ gives a concrete criterion for when medium effects begin to modify a process of a given spatial extent.
- For $T >= 6T_c$, a single constant rescaling of the two-loop running coupling describes both the Coulomb strength and the screening mass extracted from the singlet free energy, so higher-order and non-perturbative corrections appear as an overall factor there.
- Near $T_c$, models that trace the plasma's non-perturbative behavior to a large Coulomb coupling are attributing the effect to the wrong source; the relevant physics is residual confinement at intermediate distances.
- Any quoted temperature-dependent coupling for $T_c <= T <~ 2T_c$ is scheme dependent at the level of a factor of several, so such couplings should not be transported between different observables without conversion.
Reading between the lines
- If the remnant-confinement reading is right, fitting $F_1$ near $T_c$ with a linear-plus-Coulomb form should yield an effective string tension that decreases smoothly with temperature and vanishes only gradually, which is a check the paper does not perform directly.
- The whole short-distance result rests on a gauge-fixed correlator standing in for a gauge-invariant singlet free energy; a cross-check with a genuinely gauge-invariant dressed-Polyakov-loop operator, or in a different gauge, would test whether the reported temperature independence of the slope is physical rather than an artifact of the Coulomb-gauge choice.
- For quarkonium phenomenology this implies a specific ordering: the Coulombic binding of a heavy quark pair should be essentially unmodified until the screening length falls below the bound-state radius, so medium modification of the lowest-lying states should set in at a calculable temperature rather than gradually from $T_c$.
- Because the ratio $α(T)/ã(T)$ varies from about five near $T_c$ to one near $6T_c$, anyone extracting a Debye mass or a plasma coupling from lattice free energies in the intermediate temperature range should report which of the two fitted parameters they mean; tabulating the ratio as a function of temperature would make the ambiguity usable rather than merely noted.
Original abstract
We analyze the free energy of a static quark anti-quark pair in quenched QCD at short and large distances. From this we deduce running couplings, g^2(r,T), and determine the length scale that separates at high temperature the short distance perturbative regime from the large distance non-perturbative regime in the QCD plasma phase. Ambiguities in the definition of a coupling beyond the perturbative regime are discussed in their relation to phenomenological considerations on heavy quark bound states in the quark gluon plasma. Our analysis suggests that it is more appropriate to characterize the non-perturbative properties of the QCD plasma phase close to T_c in terms remnants of the confinement part of the QCD force rather than a strong Coulombic force.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
We analyze the free energy of a static quark anti-quark pair in quenched QCD at short and large distances. From this we deduce running couplings, g^2(r,T), and determine the length scale that separates at high temperature the short distance perturbative regime from the large distance non-perturbative regime in the QCD plasma phase. Ambiguities in the definition of a coupling beyond the perturbative regime are discussed in their relation to phenomenological considerations on heavy quark bound states in the quark gluon plasma. Our analysis suggests that it is more appropriate to characterize the non-perturbative properties of the QCD plasma phase close to T_c in terms remnants of the confinement part of the QCD force rather than a strong Coulombic force.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We analyze the free energy of a static quark anti-quark pair in quenched QCD at short and large distances. | contribution 0.99 | 0.94 | 0.03 | asserted 0.89 |
| s1 | From this we deduce running couplings, g^2(r,T), and determine the length scale that separates at high temperature the short distance perturbative regime from the large distance non-perturbative regime in the QCD plasma phase. | result 0.73 | 0.96 | 0.15 | asserted 1.00 |
| s2 | Ambiguities in the definition of a coupling beyond the perturbative regime are discussed in their relation to phenomenological considerations on heavy quark bound states in the quark gluon plasma. | interpretation 0.45 | 0.42 | 0.04 | unclear 0.54 |
| s3 | Our analysis suggests that it is more appropriate to characterize the non-perturbative properties of the QCD plasma phase close to T_c in terms remnants of the confinement part of the QCD force rather than a strong Coulombic force. | interpretation 0.99 | 0.86 | 0.72 | hedged possibility 1.00 |
What was examined, and what was not
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Figures
Showing 4 of the paper's 5 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:hep-lat/0406036 by the authors.
References
How later papers used it
51 later papers cite it
7 later papers by other authors are listed below: 6 used its data or values and 1 cited it as support. 2 more papers by the same authors are listed: 2 used its data or values.
Uses its data or values 8 of 14 papers with this label · 2 by the same authors
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Used the potential U(r,T) evaluated by this paper from lattice QCD results and re-parameterised it.
Semi-classical approach to $J/\psi$ suppression in high energy heavy-ion collisions (2013) · 0.84 · paraphrased: the licence does not allow quoting
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Estimated a scale as that at which this paper's lattice calculations of the running coupling coincide with the perturbative expression at a given temperature.
Bulk viscosity of QCD matter near the critical temperature (2007) · 0.86 · paraphrased: the licence does not allow quoting
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Additionally, we show lQCD estimates: quenched QCD $N_f = 0$ results (grey circles) are taken from Ref. [ref] , $N_f = 2$ (black inverted triangles) from Ref. [ref] and $N_f = 2+1$ (brown squares) from Ref. [ref] (from Fig. 7).
Extraction of the microscopic properties of quasi-particles using deep neural networks (2023) · Results: $g^2, m, γ$ and transport coefficients. · 0.96
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Adjusted the leading-order Debye mass by a factor of (1.4)^2 to account for higher-order corrections determined using this paper's lattice calculations.
Bottomonia Suppression in Heavy Ion Collisions from AdS/CFT (2017) · 0.91 · paraphrased: the licence does not allow quoting
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Adjusted the isotropic leading-order Debye mass by a factor of (1.4)^2 to account for higher-order corrections measured in this paper's lattice simulations.
Thermal Bottomonium Suppression at RHIC and LHC (2011) · 0.85 · paraphrased: the licence does not allow quoting
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The lattice results for quenched QCD, $N_f = 0$ (blue circles) are taken from Ref. [ref] , for $N_f = 2$ (orange inverted triangles) from Ref. [ref] , and for $N_f = 2+1$ (red triangles) from Ref. [ref] .
Inelastic and elastic parton scatterings in the strongly interacting quark-gluon plasma (2023) · Quasiparticle properties · 0.88
By the same authors
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Assumed a large-distance form for V(r,T) with coefficients determined in this paper.
Can quarkonia survive deconfinement ? (2007) (same authors) · 0.96 · paraphrased: the licence does not allow quoting
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Estimated a scale as that at which this paper's lattice calculations of the running coupling coincide with the perturbative expression at a given temperature.
Universal properties of bulk viscosity near the QCD phase transition (2007) (same authors) · 0.93 · paraphrased: the licence does not allow quoting
Cites it as support 1 paper
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Said its conclusion is supported by this paper's calculations of the static quark-antiquark potential.
Prediction of a Photon Peak in Heavy Ion Collisions (2008) · 1.00 · paraphrased: the licence does not allow quoting
How the literature uses it
47 arXiv papers cite this in 80 sentences
Papers citing it · 36 sentences without a confident label
Builds on it 1 paper
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Following [ref] we can generalize this approach to the free energy and singlet free energy and obtain the corresponding effective couplings.
Color screening in (2+1)-flavor QCD · The effective coupling · 0.94
Uses its method or tool 4 papers
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In this expression, $μ= G(ξ,θ) m_D$ [ref] is the anisotropic Debye mass, where $G$ is a function which depends on the degree of plasma momentum-space anisotropy $ξ$, the angle of the line connecting the quark-antiquark pair with respect to the beamline direction $θ$, and the isotropic Debye mass $m_D = 1.4 √(1+N_f/6) g_s T$ [ref] .[In the limit $ξ→0$, one has $G = 1$ and the real part of the potential above reduces to the internal energy derived from the original Karsch-Mehr-Satz potential [ref] .].
Using bottomonium production as a tomographic probe of the quark-gluon plasma · Methodology · 0.87
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According to the definitions provided in lattice QCD [ref] , the running coupling constant is defined in the so-called qq-scheme as [equation] For Figs. [ref], [ref] (a), [ref] (a), and [ref] (a) of different systems at varying temperatures with $μ=0$, we observed that before reaching the critical temperature of each system, the running coupling constant increases with the quark separation distance.
The Potential Energy of Heavy Quarkonium in Flavor-Dependent Systems from a Holographic Model · Running coupling constant · 0.81
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Similarly to papers [ref] we fix the renormalization constant $c'(μ)$ through the matching condition for $Ω_1(r, μ)$ at short distances to the short distance behavior of the interaction potential $V(r)$.
Lattice study of static quark-antiquark interactions in dense quark matter · The grand potential of a static quark-antiquark pair in dense quark matter · 0.90
Uses its data or values 13 papers
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We choose to lead this study with the potential $U(r⃗,T)$, evaluated by Kaczmarek et al. [ref] from lQCD results and re-parameterised by us.
Semi-classical approach to $J/\psi$ suppression in high energy heavy-ion collisions · The color screened potentials and temperature scenarios · 0.84
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At large distances, $rT > 1.25$ we assume that $V(r,T)$ has the form [equation] where $α_1$ and $α̃_1$ were determined in [ref] .
Can quarkonia survive deconfinement ? · Screening above deconfinement · 0.96
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Thus by estimating their dependences on temperature by using quenched (pure Yang-Mills) lattice QCD simulations [ref] , we finally get the temperature dependences of the condensates.
Charmonium ground and excited states at finite temperature from complex Borel sum rules · Finite temperature effects · 0.86
Compares with it 9 papers
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This picture qualitatively agrees with lattice result in Ref. [ref] .
Thermodynamics of deformed AdS$_5$ model with a positive/negative quadratic correction in graviton-dilaton system · The heavy quark potential · 0.98
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The static energy given by Eq. ([ref]) coincides with the leading-order result [ref] of the so-called singlet free energy first introduced by Nadkarni [ref] (the heavy quark-antiquark free energy was defined by McLerran and Svetitsky in [ref] ) and also studied in lattice QCD (see e.g. [ref] and [ref] for reviews).
Static quark-antiquark pairs at finite temperature · Singlet static energy for $1/r ∼m_D$ · 0.96
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The resulting $α_s (T)$ is displayed in the Panel (a) of Fig. [ref] and compared with QCD-lattice coupling deduced from a short-distance behavior of the singlet free energy [ref] and from spectral density of heavy-quark correlator [ref] .
Color path-integral Monte-Carlo simulations of quark-gluon plasma: Thermodynamic and transport properties · Simulations of QGP · 0.98
Cites it as support 1 paper
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This conclusion is supported by calculations of both the static quark-antiquark potential [ref] and of Minkowski-space spectral functions in lattice-regularized QCD [ref] .
Prediction of a Photon Peak in Heavy Ion Collisions · Introduction · 1.00
Cites it as background 10 papers
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After proper renormalization the expectation value of the renormalized Polyakov loop is related to the free energy, $F_Q$, of a static quark [ref] [equation] The renormalized Polyakov loop, or equivalently the free energy of a static charge $F_Q$ has been studied in SU(N) gauge theories in a wide temperature interval [ref] .
Polyakov loop in 2+1 flavor QCD from low to high temperatures · Introduction · 0.85
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In the literature there are several ways to fix this constant [ref] .
QCD Thermodynamics · The renormalized static potential in the continuum limit · 0.84
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A related topic of investigation on the lattice consists of calculating the quark-antiquark potential as a function of temperature [ref] .
Toward Large N Thermal QCD from Dual Gravity: The Heavy Quarkonium Potential · Introduction · 0.94
Discussion
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