REVIEW
Superconductivity from perturbative one-gluon exchange in high density quark matter
High Energy Physics - Phenomenology · Submitted 25 Jun 1999 · 15 references
Pith's verdict: A careful, honest derivation that turns Son's exponent into a usable formula — the g⁻⁵ prefactor is real, but its coefficient is only pinned to order one, and the authors say so.
T0 · AI review
Why Pith says this
Highlight any text to comment on it.
Referee report
The paper
The paper claims
Deriving the superconducting gap of dense quark matter from one-gluon exchange gives $g^{-5}e^{-3π²/(√2g)}$
The reading
What carries the argument
The Eliashberg equation for the gap as a function of imaginary frequency, obtained by projecting the Dyson-Schwinger equation onto the color-antitriplet, spin-singlet, positive-parity channel and reducing the momentum integral to the vicinity of the Fermi surface. The load-bearing ingredient is the hard-dense-loop gluon propagator: a longitudinal part with Debye mass $F = 2m^{2}$ and a transverse part $G$ with Landau-damping imaginary part, which together replace the schematic infrared cutoff used in earlier work. The angular integral over scattering angle then yields a logarithm $g^{2}/(18π^{2}) ∫ dq_0 log(1 + 64πμ/(N_f g^{2}|p_0-q_0|))$, whose logarithmic dependence on frequency is what forces the gap to vary with $p_0$ and produces the double-logarithmic exponent rather than a simple BCS $e^{-1/g^{2}}$.
Extended reading notes
Core claim
The paper's central claim is that the color-superconducting gap of two-flavor quark matter at asymptotically large chemical potential is $Δ ∼ g^{-5} e^{-3π^{2}/(√2 g)}$, with the coefficient in the exponent verified against Son's earlier result and the prefactor determined here. The route is a Nambu-Gorkov gap equation in which the gluon propagator is dressed with hard-dense-loop self-energies: electric modes are Debye screened at a scale $m_D$, while transverse magnetic modes are only dynamically screened, at a much smaller scale set by the gap itself. Because the angular integral is dominated by nearly collinear scattering, this magnetic screening regulates the would-be infrared divergence and produces the exponential. The authors solve the resulting integral equation numerically, first with magnetic exchange alone and then with electric exchange added, and confirm that the solution has the form of Son's approximate answer rescaled by an overall constant, in the full case with $c ≃ 1.4×10^{4}g^{-5}$. They also argue that the gap is gauge-parameter independent in this approximation, because it is fixed by quarks that are almost on shell, and that vertex corrections from hard dense loops do not alter the asymptotic form.
Load-bearing premise
The calculation assumes that leading-order truncation is enough to fix the prefactor and its coefficient: a free quark-gluon vertex, no fermion wave-function renormalization, a one-loop hard-dense-loop gluon propagator, and a running coupling evaluated by hand at the Fermi momentum. The paper itself notes that the Meissner effect will shift the numerical coefficient and that without a higher-order calculation the renormalization scale cannot be fixed, so the exponent is on firmer ground than the number in front of it.
Editorial extensions
If this is right
- The color-superconducting gap at asymptotically high density is parametrically larger than a BCS-style estimate would suggest, because the exponent is $1/g$ rather than $1/g^{2}$.
- The result fixes the overall coefficient of the $g^{-5}$ prefactor up to a factor of order one, which is what makes a numerical estimate at accessible densities possible at all.
- Because the gap grows relative to $Λ_{QCD}$ as $μ → ∞$, the magnetic screening scale stays perturbative and the weak-coupling treatment is self-consistent in the asymptotic regime.
- Extrapolating to $μ < 1$ GeV gives gaps of order 100 MeV, comparable to earlier estimates built from instanton models and schematic interactions normalized at zero density.
- The gap's dependence on frequency cannot be replaced by a constant: doing so preserves the double-logarithmic structure but gets the constant in the exponent wrong.
Reading between the lines
- If the gap really sits near 100 MeV at neutron-star densities, the pairing scale is a substantial fraction of the Fermi energy, which would make the superconducting transition temperature and the resulting cooling behavior of young neutron stars sensitive to details the asymptotic calculation cannot resolve.
- The structure of the argument suggests a natural diagnostic: the ratio of the gap to the screening scale, and the location of the crossover where $q_M$ approaches $Λ_{QCD}$, could be used to mark where weak-coupling reasoning stops being trustworthy, independently of the numerical value of the gap.
- Because the Meissner mass enters at the same parametric order as dynamic screening at finite momentum, a calculation that treats the two together would test whether the coefficient quoted here survives, rather than only whether the exponent does.
- The same Eliashberg machinery, applied to three flavors where color-flavor locking gaps all gluons, could be run with the full Higgsed gluon spectrum to see whether the exponent is unchanged and only the prefactor shifts.
Original abstract
We study color superconductivity in QCD at asymptotically large chemical potential. In this limit, pairing is dominated by perturbative one-gluon exchange. We derive the Eliashberg equation for the pairing gap and solve this equation numerically. Taking into account both magnetic and electric gluon exchanges, we find $\Delta\sim g^{-5}\exp(-c/g)$ with $c=3\pi^2/\sqrt{2}$, verifying a recent result by Son. For chemical potentials that are of physical interest, $\mu< 1$ GeV, the calculation ceases to be reliable quantitatively, but our results suggest that the gap can be as large as 100 MeV.
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 study color superconductivity in QCD at asymptotically large chemical potential. In this limit, pairing is dominated by perturbative one-gluon exchange. We derive the Eliashberg equation for the pairing gap and solve this equation numerically. Taking into account both magnetic and electric gluon exchanges, we find $\Delta\sim g^{-5}\exp(-c/g)$ with $c=3\pi^2/\sqrt{2}$, verifying a recent result by Son. For chemical potentials that are of physical interest, $\mu< 1$ GeV, the calculation ceases to be reliable quantitatively, but our results suggest that the gap can be as large as 100 MeV.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We study color superconductivity in QCD at asymptotically large chemical potential. | contribution 0.79 | 0.87 | 0.04 | asserted 0.77 |
| s1 | In this limit, pairing is dominated by perturbative one-gluon exchange. | background 0.91 | 0.11 | 0.07 | asserted 1.00 |
| s2 | We derive the Eliashberg equation for the pairing gap and solve this equation numerically. | method 0.96 | 0.97 | 0.06 | asserted 1.00 |
| s3 | Taking into account both magnetic and electric gluon exchanges, we find $\Delta\sim g^{-5}\exp(-c/g)$ with $c=3\pi^2/\sqrt{2}$, verifying a recent result by Son. | result 1.00 | 0.92 | 0.73 | asserted 1.00 |
| s4 | For chemical potentials that are of physical interest, $\mu< 1$ GeV, the calculation ceases to be reliable quantitatively, but our results suggest that the gap can be as large as 100 MeV. | limitation 0.95 | 0.77 | 0.18 | hedged possibility 1.00 |
What was examined, and what was not
- arXiv listing abstract v3
- full text
- figures and tables
- references and citing sentences
- relations to other papers
- P abstract
- S sections
- T body sentences
- C citations
- R cross-paper relations
Figures
Showing 3 of the paper's 6 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:hep-ph/9906512 by the authors.
References
How the literature uses it
32 arXiv papers cite this in 58 sentences
Papers citing it · 38 sentences without a confident label
Uses its method or tool 1 paper
-
To resolve this, one may integrate the momenta about the Fermi surface as often done in QCD studies at high densities in the presence of a Cooper instability, see, e.g., Refs. [ref] .
Pressure and speed of sound in two-flavor color-superconducting quark matter at next-to-leading order · Two-loop Contribution to the Effective Potential · 0.84
Uses its data or values 1 paper
-
The dependence of $Δ$ on $g$ has been computed as $Δ∼μg^-5 ^-c/g$ with $c=3π^2/√(2)$ for $N_c=3$ and $c=2π^2$ for $N_c=2$ [ref] .
Overscreened Kondo effect, (color) superconductivity and Shiba states in Dirac metals and quark matter · Taxonomy of impurity states in multichannel (color) superconductors · 0.93
Compares with it 2 papers
-
It is interesting to compare this results to the one gluon exchange perturbative calculations [ref] .
Asymptotically conformal CFL quark matter within a nonlocal chiral quark model · Nonlocal NJL model at high densities · 1.00
-
With this choice of parameters we get $Δ(p=0)∼20-40$ MeV in the range of $μ$ considered here, in agreement with previous studies [ref] .
Topological Susceptibility in the Superconductive Phases of Quantum Chromodynamics: a Dyson-Schwinger Perspective · Solution of the Gap Equation for the CFL Phase · 0.97
Cites it as background 15 papers
-
We also apply the model to modelling the color-superconducting color-flavor-locked (CFL) phase of quark matter [ref] , which is expected to be the ground state of dense QCD [ref] .
Asymptotically conformal CFL quark matter within a nonlocal chiral quark model · Introduction · 0.80
-
Non-perturbative phenomenon in particular color superconductivity [ref] is believed to be active
Bayesian evidence for two peaks in the sound speed in cold dense QCD · Introduction · 0.96
-
In this work, we compute $χ$ in superdense phases of QCD, in which the system could be in a color-superconductive phase [ref] .
Topological Susceptibility in the Superconductive Phases of Quantum Chromodynamics: a Dyson-Schwinger Perspective · Introduction · 0.92
Discussion
Disagree with the review, or know something it missed? Leave a comment, highlight any passage above to comment on it, or challenge this review formally.