REVIEW
Chiral Dynamics of Baryons from String Theory
High Energy Physics - Theory · Submitted 30 Jan 2007 · 15 references
Pith's verdict: The structural claim — g_A and the magnetic moment both scale as N_c with no λ or MKK dependence — is the part worth citing; the numerical agreement with experiment rests on a shift the authors themselves call an assumption.
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The paper
The paper claims
Treating baryons as instantons in the Sakai-Sugimoto holographic QCD model yields a five-dimensional magnetic coupling that reproduces the axial coupling g_A and magnetic moments as quantities proportional to Nc.
The reading
Extended reading notes
Core claim
The instanton interpretation of the baryon in the Sakai-Sugimoto model implies a specific five-dimensional magnetic coupling (Eq. 10) with g5(0) = 2 pi^2 / 3, fixed by matching the baryon bilinear to the instanton's long-range field. Dimensional reduction then gives g_A approximately 0.7 (Nc/3) and the anomalous magnetic moment approximately 0.36 Nc / MKK, both proportional to Nc and independent of the 't Hooft coupling lambda and the Kaluza-Klein scale MKK.
Load-bearing premise
The coefficient g5(0) = 2 pi^2 / 3 is fixed by a matching argument that the paper says is 'mathematically identical' to the Adkins-Nappi-Witten treatment of the Skyrme model, but the step from the collective-coordinate expectation value to the numerical coefficient is sketched in one paragraph (Five-dimensional effective action of baryons). If this normalization is off, every coupling estimate in the paper scales with it.
Original abstract
We study baryons in an AdS/CFT model of QCD by Sakai and Sugimoto, realized as small instantons with fundamental string hairs. We introduce an effective field theory of the baryons in the five-dimensional setting, and show that the instanton interpretation implies a particular magnetic coupling. Dimensional reduction to four dimensions reproduces the usual chiral effective action, and in particular we estimate the axial coupling $g_A$ between baryons and pions and the magnetic dipole moments, both of which are proportional to $N_c$. We extrapolate to finite $N_c$ and discuss subleading corrections.
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 baryons in an AdS/CFT model of QCD by Sakai and Sugimoto, realized as small instantons with fundamental string hairs. We introduce an effective field theory of the baryons in the five-dimensional setting, and show that the instanton interpretation implies a particular magnetic coupling. Dimensional reduction to four dimensions reproduces the usual chiral effective action, and in particular we estimate the axial coupling $g_A$ between baryons and pions and the magnetic dipole moments, both of which are proportional to $N_c$. We extrapolate to finite $N_c$ and discuss subleading corrections.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We study baryons in an AdS/CFT model of QCD by Sakai and Sugimoto, realized as small instantons with fundamental string hairs. | contribution 0.71 | 0.69 | 0.07 | asserted 0.98 |
| s1 | We introduce an effective field theory of the baryons in the five-dimensional setting, and show that the instanton interpretation implies a particular magnetic coupling. | contribution 0.78 | 0.95 | 0.22 | asserted 1.00 |
| s2 | Dimensional reduction to four dimensions reproduces the usual chiral effective action, and in particular we estimate the axial coupling $g_A$ between baryons and pions and the magnetic dipole moments, both of which are proportional to $N_c$. | result 0.96 | 0.92 | 0.44 | asserted 0.99 |
| s3 | We extrapolate to finite $N_c$ and discuss subleading corrections. | contribution 0.77 | 0.87 | 0.07 | unclear 0.54 |
What was examined, and what was not
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References
How the literature uses it
67 arXiv papers cite this in 160 sentences
Papers citing it · 101 sentences without a confident label
Builds on it 3 papers
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In this paper, we generalize the derivation of the interactions between mesons and nucleons carried out in Ref. [ref] to the interactions between mesons and baryons of arbitrary half-integer spins for the two-flavor case ($N_F=2$).
A Holographic QCD and Excited Baryons from String Theory · Summary · 1.00
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Our solution is an extension of the $N_f=2$ solution of [ref] to a generic $N_f$,[ The baryon solution in the $N_f=2$ case is also analyzed in [ref] .
Baryons and the Chern-Simons term in holographic QCD with three flavors · Classical solution representing a baryon · 1.00
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This analysis was later extended to other holographic models obtained from string theory, such as the Witten-Sakai-Sugimoto (WSS) model [ref] , with similar conclusions [ref] .
Holography in Quark-Gluon Plasma and Neutron Stars · Holography · 0.86
Uses its method or tool 3 papers
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As shown in [ref] , one can replace the form factors by an infinite sum of vector-meson exchanges [ref] , if we expand the nonnormalizable photon field in terms of the normalizable vector meson $ψ_(2k+1)$ of mass $m_2k+1$ as [equation] where the decay constant of the $k$-th vector mesons is given as $g_v^(k)=m_2k+1^2ζ_k$ with [equation] where $U_KK$ is a parameter of the SS model and [equation] The resulting EM form factors then take the form
Integrating Holographic Vector Dominance to Hidden Local Symmetry for the Nucleon Form Factor · Holographic Form Factors · 0.81
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The computation of the spectrum, as well as the quantization procedure, closely follow the soliton approach of [ref] , although the derivation of the Hamiltonian is different.
A Matrix Model for Baryons and Nuclear Forces · Single baryon · 0.97
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In next section, we will derive the proposed effective action by generalizing a method originally due to Adkins, Nappi, and Witten [ref] and also adapted for holographic Nucleons in Refs. [ref] .
A Holographic QCD and Excited Baryons from String Theory · Effective Field Theory of the Instanton Soliton · 0.87
Uses its data or values 7 papers
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Now turning to hVD, we will use the results of [ref] given in Table [ref] reproduced from [ref] .
Integrating Holographic Vector Dominance to Hidden Local Symmetry for the Nucleon Form Factor · sVD and hVD predictions · 0.99
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Remember that the holographic size of the solitonic baryon is $≃9.6/(M_KK√(λ))$, where $λ$ is the 't Hooft coupling and $M_KK∼1$ GeV is the mass scale of the vector mesons [ref] .
A Matrix Model for Baryons and Nuclear Forces · Introduction · 0.95
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For illustration purpose, we will take $λN_c=50$ as in [ref] .
Four-nucleon contact interactions from holographic QCD · Numerical results · 0.94
Compares with it 3 papers
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Our prediction for $g_A$, whose experimental value is about 1.27, is [ref] [equation] With a subleading correction added, the extrapolated value is 0.84 which is about 30% better than Adkins-Nappi-Witten estimate [ref] based on the vanilla Skyrmion but worse than an improved Skyrmion dressed by the lowest lying $ρ$ meson with phenomenologically determined couplings [ref] .
Precision Holographic Baryons · Numbers and Comments · 0.99
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To order $ħ^0$ the current is entirely vector meson dominated in overall agreement with the effective analysis in [ref] .
Electromagnetic Baryon Form Factors from Holographic QCD · Introduction · 0.90
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The Hamiltonian [ref] for the instanton size modulus $ρ$ and the instanton location $Z$ along the $x^4$ direction is [equation] again without the rest mass term $λN_c M_KK/27π$.
A Matrix Model for Baryons and Nuclear Forces · Two flavors · 0.99
Cites it as support 4 papers
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For the case of $s=1/2$, it was shown in [ref] that a direct coupling to the field strength $F=dA+iA^2$ to a bilinear of the spinor emulates this long range behavior of the quantized soliton.
A Holographic QCD and Excited Baryons from String Theory · Nonrelativistic Lagrangian · 0.96
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As shown in [ref] , the Pauli term therefore should not contain the $U(1)$ gauge fields to reproduce the correct behavior of non-abelian instanton solitons at long distances, which leads to important sum rules for both the electric dipole moments and the anomalous magnetic moments of nucleons, which are model-independent and not subject to any $1/N_c$ corrections, [equation]
The Electric Dipole Moment of the Nucleons in Holographic QCD · Discussion and Conclusion · 0.98
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Although we do not elaborate on the derivation here, we emphasize that not only the structure of the operator $B̅γ·FB$ (which happens to be also unique at dimension six level) but also the coefficient function have been derived rigorously [ref] .
Precision Holographic Baryons · An Effective Theory of Holographic Baryons · 0.97
Cites it as background 29 papers
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As discussed extensively in [ref] and [ref] , the SU$(2)$ YM instanton in a curved space will generally collapse to zero size, in contrast to the situation in the flat space.
Skyrmion properties from holographic instantons of large size · Skyrmion properties from holographic instanton · 0.90
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Baryons were introduced in the model in [ref] , while in the context of AdS/CFT correspondence description of baryons in terms of D-branes has a much longer history [ref] .
Holographic Nuclei · Gauge theory on nucleus · 0.93
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To be specific, we are considering the popular top-down holographic QCD model, namely that of Witten-Sakai-Sugimoto (WSS) [ref] [ See also Refs. [ref] for a derivation of the chiral effective action from the WSS model, as well as an estimate of the axial coupling, magnetic dipole moments, electromagnetic form factors and vector dominance. ].
Boundary terms in the Witten-Sakai-Sugimoto model at finite density · Introduction · 0.89
Discussion
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