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The transition temperature in QCD

High Energy Physics - Lattice · Submitted 22 Aug 2006 · 28 references

Pith's verdict: A careful, well-documented lattice determination of Tc that mostly holds up; the continuum extrapolation from two spacings is the one place I'd push.

T0 · AI review

How this review was made: An AI referee (selfhosted/deepseek-v4.1-flash) read the paper on November 11, 2026 and answered a fixed list of questions about it. T0 is the starting level every paper gets. The levels describe how deeply Pith has checked the paper, never the authors.

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  4. T3 Formal statement The claims written out in a formal math language a computer can read.
  5. T4 Proof Those claims proved, and the proof checked by computer.

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arXiv IDhep-lat/0608013 (version 3)
Pith IDQTMOGLEH, Pith's permanent record of this paper and its review
CitationC. Jung, C. Miao, C. Schmidt, E. Laermann, F. Karsch, J. van der Heide, K. Petrov, M. Cheng, N. H. Christ, O. Kaczmarek, P. Petreczky, R. D. Mawhinney, S. Datta, T. Umeda. "The transition temperature in QCD." arXiv:hep-lat/0608013 (2006). https://pith.science/paper/QTMOGLEH
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Referee report
The paper

The paper claims

The paper computes the temperature at which QCD turns into a quark-gluon plasma, using lattice simulations with two light quarks and a physical strange quark, and reports $T_c = 192(7)(4)$ MeV at the physical quark masses.

The reading

The paper sets out to compute, from first principles, the temperature at which strongly interacting matter stops being a gas of hadrons and becomes a quark-gluon plasma, for the quark masses that actually occur in nature: two light quarks plus a heavier strange one. The authors simulate the theory on space-time lattices with two different temporal extents, $N_𝜏 = 4$ and $6$, locate the crossover on each by watching where the chiral and Polyakov-loop susceptibilities peak, and convert lattice units into physical ones using the scale $r_0$ extracted from the zero-temperature static quark potential. Combining an extrapolation to vanishing light-quark mass with an extrapolation to vanishing lattice spacing gives $T_c r_0 = 0.457(7)$ at the physical point, which with $r_0 = 0.469(7)$ fm becomes $T_c = 192(7)(4)$ MeV. The number matters because it is a first-principles anchor for the whole picture of heavy-ion collisions: it says where the plasma forms, and it sits about 10 percent above the $175$ MeV value then in common use, largely because of a newer calibration of $r_0$.

What carries the argument

The load-bearing device is the joint fit in Eq. 13, $Y = Y_{0,m_s,\infty} + A(m_{ps} r_0)^d + B/N_𝜏^2$ with $Y = T_c r_0$ or $T_c/\sqrt{\sigma}$, which folds the light-quark extrapolation and the continuum extrapolation into one two-parameter-plus-offset form. The exponent $d = 2/\beta\delta \simeq 1.08$ comes from O(4) universal scaling; the authors bracket the systematic by repeating the fit with $d = 1$ and $d = 2$ (the first-order case) and quoting the spread. The critical coupling for each parameter set is the average of the peak positions in the Polyakov-loop susceptibility and the disconnected light-quark chiral susceptibility, with peaks located by Ferrenberg-Swendsen reweighting and errors from jackknife resampling; the split between the two peaks is added as a systematic. The scale $r_0$, defined by $r^2 dV_{\bar{q}q}/dr = 1.65$ at $r = r_0$, is obtained from Cornell-type fits to the static quark potential with lattice distortions handled by replacing the Euclidean distance with the lattice Coulomb potential of Eq. 8, and interpolated in coupling and quark mass through the renormalization-group-inspired ansatz of Eq. 12. Simulations use the p4fat3 improved staggered action with the exact RHMC algorithm, which removes the finite step-size errors of the earlier hybrid-R runs.

Extended reading notes

Core claim

The central claim is a controlled determination of the QCD transition temperature at physical quark masses. The authors report $T_c r_0 = 0.457(7)^{+8}_{-2}$ at $m_{ps} r_0 = 0.321(5)$, equivalently $T_c/\sqrt{\sigma} = 0.408(8)^{+3}_{-1}$, and $T_c r_0 = 0.444(6)^{+12}_{-3}$ in the chiral limit, about 3 percent lower. Converting with $r_0 = 0.469(7)$ fm gives $T_c = 192(7)(4)$ MeV, where the second error is the authors' estimate of residual cutoff effects. Three supporting observations carry the result: the $N_𝜏 = 6$ values sit systematically 3 to 4 percent below the $N_𝜏 = 4$ values at matched pion mass, as a nonzero lattice spacing should produce; results at $\hat{m}_s = 0.1$ and $0.065$ agree within errors even though the kaon mass differs by about 20 percent, so the answer is insensitive to the exact strange mass; and the peaks in the light and strange quark susceptibilities coincide to within about 1 MeV, so a single temperature describes both sectors. The authors also note that their $r_0/\sqrt{\sigma} \simeq 1.11$ implies $\sqrt{\sigma} \simeq 465$ MeV, roughly 10 percent above the string tension used in earlier scale settings, which is where most of the upward shift from 175 MeV comes from.

Load-bearing premise

The continuum extrapolation rests on only two lattice spacings, $N_𝜏 = 4$ and $6$, fitted with a single $1/N_𝜏^2$ term, so the claimed 2 percent residual cutoff uncertainty is an estimate that no third spacing is available to check.

Editorial extensions

If this is right

  • A single transition temperature governs both the light and strange sectors: the peaks in the two susceptibilities agree to within about 1 MeV, so phenomenological models that split the two crossover temperatures are not supported at this precision.
  • The chiral-limit value is about 3 percent below the physical-point value, so any comparison with experiment should use $T_c r_0 = 0.457(7)$ rather than the easier-to-compute chiral number.
  • The ratio $T_c/\sqrt{\sigma} = 0.408(8)$ is independent of any experimental calibration, so it survives even if the fm conversion is later revised.
  • Since the fit gives $B \approx 1/3$, results on $N_𝜏 = 4$ lattices run about 5 percent high and $N_𝜏 = 6$ about 2 percent high, which sets the correction future coarse-lattice work should expect.
  • Combined with freeze-out temperatures below 170 MeV inferred from particle yields at RHIC, a transition at 192 MeV leaves room for an intermediate hadronic stage between the crossover and chemical freeze-out.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The headline shift from roughly 175 MeV to 192 MeV is driven mostly by the $r_0$ calibration rather than by the lattice data, so the more durable output of this paper is the dimensionless $T_c r_0$; any future revision of $r_0$ moves the MeV number proportionally and should be read as a scale recalibration, not a contradiction of this result.
  • With only two lattice spacings, a $1/N_𝜏^2$ term and a $1/N_𝜏^4$ term are indistinguishable; a single $N_𝜏 = 8$ run with the same action would be the cheapest decisive test, and the sign and size of the shift it produces would calibrate how much to trust the quoted 2 percent residual-cutoff estimate elsewhere.
  • The fit's weak preference for $d \approx 0.6$, below the O(4) value of 1.08, is plausibly a symptom of the coarse light-quark masses rather than evidence against O(4) scaling; extending the light-mass range downward would sharpen the exponent and, incidentally, test whether the transition stays a crossover at the physical strange mass.
  • The 2 percent continuum-extrapolation error is an estimate rather than a measured quantity, so downstream users who fold this $T_c$ into error budgets for, say, hydrodynamic models of heavy-ion collisions should treat the total uncertainty as somewhat larger than the quoted $(7)(4)$ MeV.
Original abstract

We present a detailed calculation of the transition temperature in QCD with two light and one heavier (strange) quark mass on lattices with temporal extent N_t =4 and 6. Calculations with improved staggered fermions have been performed for various light to strange quark mass ratios in the range, 0.05 <= m_l/m_s <= 0.5, and with a strange quark mass fixed close to its physical value. From a combined extrapolation to the chiral (m_l -> 0) and continuum (aT = 1/N_t -> 0) limits we find for the transition temperature at the physical point T_c r_0 = 0.457(7) where the scale is set by the Sommer-scale parameter r_0 defined as the distance in the static quark potential at which the slope takes on the value, (dV_qq(r)/dr)_r=r_0 = 1.65/r_0^2. Using the currently best known value for r_0 this translates to a transition temperature T_c = 192(7)(4)MeV. The transition temperature in the chiral limit is about 3% smaller. We discuss current ambiguities in the determination of T_c in physical units and also comment on the universal scaling behavior of thermodynamic quantities in the chiral limit.

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.

Compiled by classifier-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 5,181 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.03 · states limitation 0.58 · human participants 0.01 · controlled comparison 0.04 · randomized assignment 0.01 · states quantitative result 0.99 · compares with prior results 0.20 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v3. Results and the main claim are underlined; .

We present a detailed calculation of the transition temperature in QCD with two light and one heavier (strange) quark mass on lattices with temporal extent N_t =4 and 6. Calculations with improved staggered fermions have been performed for various light to strange quark mass ratios in the range, 0.05 <= m_l/m_s <= 0.5, and with a strange quark mass fixed close to its physical value. From a combined extrapolation to the chiral (m_l -> 0) and continuum (aT = 1/N_t -> 0) limits we find for the transition temperature at the physical point T_c r_0 = 0.457(7) where the scale is set by the Sommer-scale parameter r_0 defined as the distance in the static quark potential at which the slope takes on the value, (dV_qq(r)/dr)_r=r_0 = 1.65/r_0^2. Using the currently best known value for r_0 this translates to a transition temperature T_c = 192(7)(4)MeV. The transition temperature in the chiral limit is about 3% smaller. We discuss current ambiguities in the determination of T_c in physical units and also comment on the universal scaling behavior of thermodynamic quantities in the chiral limit.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#sentencerolethe authors' own workstates the main conclusionstrength
s0 We present a detailed calculation of the transition temperature in QCD with two light and one heavier (strange) quark mass on lattices with temporal extent N_t =4 and 6. contribution 0.96 0.96 0.06 asserted 0.98
s1 Calculations with improved staggered fermions have been performed for various light to strange quark mass ratios in the range, 0.05 <= m_l/m_s <= 0.5, and with a strange quark mass fixed close to its physical value. method 0.93 0.89 0.02 asserted 0.99
s2 From a combined extrapolation to the chiral (m_l -> 0) and continuum (aT = 1/N_t -> 0) limits we find for the transition temperature at the physical point T_c r_0 = 0.457(7) where the scale is set by the Sommer-scale parameter r_0 defined as the distance in the static quark potential at which the slope takes on the value, (dV_qq(r)/dr)_r=r_0 = 1.65/r_0^2. result 1.00 0.97 0.84 asserted 1.00
s3 Using the currently best known value for r_0 this translates to a transition temperature T_c = 192(7)(4)MeV. result 1.00 0.88 0.48 asserted 1.00
s4 The transition temperature in the chiral limit is about 3% smaller. result 1.00 0.89 0.06 asserted 0.94
s5 We discuss current ambiguities in the determination of T_c in physical units and also comment on the universal scaling behavior of thermodynamic quantities in the chiral limit. interpretation 0.68 0.25 0.03 unclear 0.77

What kind of paper the classifier reports this is: simulation study 1.00 · evidence from simulation or computation 1.00.

What was examined, and what was not

sources read
  • arXiv listing abstract v3
not examined
  • full text
  • figures and tables
  • references and citing sentences
  • relations to other papers
levels run
  • P abstract
not run
  • S sections
  • T body sentences
  • C citations
  • R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures
Figure 1. FIG. 1: Time history of the light and strange quark chiral con
Figure 2. FIG. 2: The light quark chiral condensate in units of
Figure 3. FIG. 3: The disconnected part of the light quark chiral susce
Figure 4. FIG. 4: The disconnected part of the light quark chiral susce
Figure 5. FIG. 5: The difference of gauge couplings at the location of pe
Figure 6. FIG. 6: The square of the kaon mass in units of

Showing 6 of the paper's 7 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:hep-lat/0608013 by the authors.

References
How later papers used it

64 later papers cite it

Evidence: substantial. 61 of the citing papers share no author with it, and 15 of those carry a confident label from Pith's citation classifier.

Pith read 15 of the 74 citing sentences, choosing only those whose citation markers point at this paper alone, and wrote the paraphrases from them. The summary, the counts, the evidence level, the links and the quotes come from code; the summary counts the papers listed below. A later paper is listed under a label when Pith's citation classifier gives one of its sentences that label at probability 0.8 or more (0.95 for support), Pith's reading finds that the citing paper itself did it, and a second check confirms the paraphrase against the sentence. This section lists uses only. It does not list criticism or disagreement, so their absence here says nothing about how the paper has been received. Papers that share an author with this one are listed apart, under "By the same authors". A quote is the citing authors' own sentence, shown when their paper's licence is CC BY, CC BY-SA or CC0. JSON

Uses its data or values 2 of 10 papers with this label · 1 by the same authors

By the same authors

How the literature uses it

53 arXiv papers cite this in 63 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers whose main result relates to this one's

Found among the papers closest to this one by title and main claim. Pith's classifier compared each pair's main results and a second model family confirmed the relation; checked against two further families, shown conflicts agreed 118 times in 120 and shown same results 218 times in 239. The quoted sentence is the other paper's main claim.

States the same result 1 paper

Papers citing it · 34 sentences without a confident label

Uses its data or values 9 papers
  • Our strategy is linearly map $(∙)_q, SB$ to the corresponding quantities of the $g_q = 37 + 14.25$ ideal gas model, and map the $f_q = f_h$ and $s_q = s_h$ horizontal lines in Fig. [ref] and [ref] to the $g_h = 3 + 14.25$ ideal gas model, where $g_q$ and $g_h$ are the degrees of freedom of the real world at $T = T_dec ≃192 MeV$ [ref] before and after the confinement/deconfinement phase transition.

    AdS/CFT aspects of the cosmological QCD phase transition · The Nucleation Rate · 0.91

  • At $T=0$ and $μ_B=0$, $$ can be evaluated by QCD sume rules [ref] : $≃0.012 ±0.006$ GeV$^4$ [ref] , corresponding to a typical scale $≃()^1/4 = 330$ MeV.

    Unruh thermalization, gluon condensation and freeze-out · 2. String tension and gluon condensate at finite density · 0.92

  • Here one finds the average value $σ≃0.19 ±0.03$ GeV$^2$ [ref] , which with eq.

    Hadron Freeze-Out and Unruh Radiation · Introduction · 0.99

Compares with it 6 papers
Cites it as support 1 paper
  • It has been established by lattice calculations that at the physical values of light and strange quark masses at zero baryon chemical potential the transition from the hadronic into the deconfined phase of QCD is a rapid crossover rather than a genuine phase transition [ref] .

    Lattice QCD at Non-Zero Temperature · Chiral crossover · 0.96

Cites it as background 12 papers

Discussion

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