REVIEW
Vacuum Instability in Electric Fields via AdS/CFT: Euler-Heisenberg Lagrangian and Planckian Thermalization
High Energy Physics - Theory · Submitted 28 Jul 2013 · 74 references
Pith's verdict: The static Euler-Heisenberg results are the real contribution; the 'Planckian thermalization' claim is mostly horizon kinematics dressed as dynamics.
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Referee report
The paper
The paper claims
A strongly coupled vacuum in a strong electric field decays, and the decay rate matches the textbook Schwinger formula once the electron mass is replaced by the quark confining force.
The reading
What carries the argument
The load-bearing object is the Dirac–Born–Infeld action of a probe D7-brane in the $AdS_5 times S^5$ (or $AdS_5$ black hole) geometry, evaluated on a constant electric field configuration with zero induced current. Because the action carries a square root, it becomes imaginary wherever the argument of the root goes negative; the boundary of that region, $z = z_*$ in the massless case and $z = z_0$ in the massive case, is the entire content of the decay rate. The complementary machinery is the reality condition on the same action: a stable steady state with nonzero current exists exactly when the numerator and denominator of the root change sign at the same radial position, which fixes the current–voltage curve. For the time-dependent part, the argument is carried by the effective metric that gauge fluctuations on the brane feel, and by the apparent horizon defined as the surface whose volume is stationary under null propagation, with the effective Hawking temperature read from its position.
Extended reading notes
Core claim
The central claim is that the full nonlinear electromagnetic response of a strongly coupled confining theory — including its vacuum decay rate — is captured by a classical D-brane action, and that this response has an unexpectedly close numerical relationship to one-loop QED. Concretely: the imaginary part of the D7-brane effective Lagrangian vanishes below a critical field $E_{cr} = (2^{1/2} pi / lambda^{1/2}) m_q^2$, which coincides with the quark–antiquark confining force computed independently from a small Wilson loop in the same model. Above threshold, the massless-case imaginary part is $Im L = N_c E^2/(32 pi)$, exactly the massless limit of the Schwinger result for the $N=2$ hypermultiplet content, and the massive case reproduces the leading and subleading terms of the QED expansion under $E_{cr} leftrightarrow m_e^2$. On top of the static result, the paper reports a dynamical one: after an abrupt switch-on of the field the current overshoots, relaxes to the steady value fixed by the reality condition on the brane action, and an apparent horizon forms on the brane whose associated temperature governs the relaxation time, $tau_{th} sim a hbar/(k_B T_eff^{infty}) sim E^{-1/2}$, numerically giving about $1$ fm/c for a RHIC-scale field.
Load-bearing premise
The thermalization claim rests on the probe approximation: the flavor brane sits in a fixed background with the gluon sector at zero temperature, and the temperature read off the brane's apparent horizon is assumed to be the scale that actually governs how fast the quark degrees of freedom relax.
Editorial extensions
If this is right
- The threshold for electric breakdown of a confining vacuum is the confining force itself, not a constituent mass, giving a sharp criterion that any confining theory should satisfy.
- The imaginary part of the effective Lagrangian for a strongly coupled theory can be computed from a classical bulk action rather than a loop diagram, because removing the color branes caps the worldsheet cylinder into a disk.
- For fields far above threshold the decay rate is a power law in $E$ rather than exponentially suppressed, so a strongly coupled vacuum is far more fragile at large field than QED intuition suggests.
- The relaxation time of the nonequilibrium current-carrying state is bounded below by $hbar/(k_B T_eff)$, which for RHIC-scale fields comes out near $1$ fm/c, in the range hydrodynamics requires.
- The same framework yields the full nonlinear effective Lagrangian below threshold as an infinite series in $E^2/E_{cr}^2$, i.e. a tower of nonlinear optical response coefficients for the strongly coupled vacuum.
Reading between the lines
- The agreement with the QED dilogarithm expansion at subleading order is striking enough that it invites a structural explanation: the DBI square root may be doing the work of the proper-time integral in the Schwinger calculation, so the coincidence could reflect a shared worldline geometry rather than an accident of the $N=2$ matter content.
- If the effective temperature really is the noise temperature of the current-carrying steady state, then the same quantity should appear in meson spectral functions and current noise on the brane, which would give an independent, non-thermalization-based measurement of $T_eff$.
- The $E^{-1/2}$ scaling is dimensionally forced once the only scale is the field, so a sharper test is the prefactor: whether the constant $a$ is universal across confining holographic models or depends on the brane embedding.
- The paper's own estimate of about $1$ fm/c uses a small 't Hooft coupling, $lambda = 10$, which sits outside the regime where the gravity description is controlled; the number should be read as an order-of-magnitude consistency check rather than a prediction.
Original abstract
We analyze vacuum instability of strongly coupled gauge theories in a constant electric field using AdS/CFT correspondence. The model is the N=2 1-flavor supersymmetric large N_c QCD in the strong 't Hooft coupling limit. We calculate the Euler-Heisenberg effective Lagrangian L(E), which encodes the nonlinear response and the quantum decay rate of the vacuum in a background electric field E, from the complex D-brane action in AdS/CFT. We find that the decay rate given by Im L(E) becomes nonzero above a critical electric field set by the confining force between quarks. A large-E expansion of Im L(E) is found to coincide with that of the Schwinger effects in QED, replacing its electron mass by the confining force. Then, the time-dependent response of the system in a strong electric field is solved non-perturbatively, and we observe a universal thermalization at a shortest timescale "Planckian thermalization time" t ~ 1/T ~ E^{-1/2}. Here, T is an effective temperature which quarks feel in the nonequilibrium state with nonzero electric current, calculated in AdS/CFT as a Hawking temperature. Stronger electric fields accelerate the thermalization, and for a realistic value of the electric field in RHIC experiment, we obtain t ~ 1 [fm/c], which is consistent with the believed value.
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 vacuum instability of strongly coupled gauge theories in a constant electric field using AdS/CFT correspondence. The model is the N=2 1-flavor supersymmetric large N_c QCD in the strong 't Hooft coupling limit. We calculate the Euler-Heisenberg effective Lagrangian L(E), which encodes the nonlinear response and the quantum decay rate of the vacuum in a background electric field E, from the complex D-brane action in AdS/CFT. We find that the decay rate given by Im L(E) becomes nonzero above a critical electric field set by the confining force between quarks. A large-E expansion of Im L(E) is found to coincide with that of the Schwinger effects in QED, replacing its electron mass by the confining force. Then, the time-dependent response of the system in a strong electric field is solved non-perturbatively, and we observe a universal thermalization at a shortest timescale "Planckian thermalization time" t ~ 1/T ~ E^{-1/2}. Here, T is an effective temperature which quarks feel in the nonequilibrium state with nonzero electric current, calculated in AdS/CFT as a Hawking temperature. Stronger electric fields accelerate the thermalization, and for a realistic value of the electric field in RHIC experiment, we obtain t ~ 1 [fm/c], which is consistent with the believed value.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We analyze vacuum instability of strongly coupled gauge theories in a constant electric field using AdS/CFT correspondence. | contribution 0.96 | 0.92 | 0.06 | asserted 0.90 |
| s1 | The model is the N=2 1-flavor supersymmetric large N_c QCD in the strong 't Hooft coupling limit. | method 0.94 | 0.20 | 0.02 | asserted 1.00 |
| s2 | We calculate the Euler-Heisenberg effective Lagrangian L(E), which encodes the nonlinear response and the quantum decay rate of the vacuum in a background electric field E, from the complex D-brane action in AdS/CFT. | method 0.57 | 0.95 | 0.10 | asserted 1.00 |
| s3 | We find that the decay rate given by Im L(E) becomes nonzero above a critical electric field set by the confining force between quarks. | result 1.00 | 0.95 | 0.29 | asserted 1.00 |
| s4 | A large-E expansion of Im L(E) is found to coincide with that of the Schwinger effects in QED, replacing its electron mass by the confining force. | result 0.96 | 0.93 | 0.13 | asserted 1.00 |
| s5 | Then, the time-dependent response of the system in a strong electric field is solved non-perturbatively, and we observe a universal thermalization at a shortest timescale "Planckian thermalization time" t ~ 1/T ~ E^{-1/2}. | result 0.94 | 0.95 | 0.39 | asserted 1.00 |
| s6 | Here, T is an effective temperature which quarks feel in the nonequilibrium state with nonzero electric current, calculated in AdS/CFT as a Hawking temperature. | interpretation 0.58 | 0.86 | 0.08 | asserted 0.99 |
| s7 | Stronger electric fields accelerate the thermalization, and for a realistic value of the electric field in RHIC experiment, we obtain t ~ 1 [fm/c], which is consistent with the believed value. | result 0.92 | 0.90 | 0.18 | hedged possibility 0.61 |
What was examined, and what was not
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Figures
Figures reproduced from arXiv:1307.7423 by the authors.
References
How the literature uses it
39 arXiv papers cite this in 101 sentences
Papers citing it · 64 sentences without a confident label
Uses its method or tool 5 papers
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An alternative approach is the Hashimoto-Oka method [ref] which associates vacuum instability with the imaginary part of the effective action for the flavor probe brane.
Thermal quench of a dynamical QCD model in an external electric field · Introduction · 0.95
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Then, as proposed in [ref] , the decay rate is given by the imaginary part of the DBI action of the original probe brane configuration with a U(1) field turned on.
Notes on holographic Schwinger effect · Probe D7 brane and confining D3-branes · 0.88
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Regarding this argument (and following [ref] ), we set $j=0$ in the action [ref] and study its possible imaginary part.
Equilibrium Instability of Chiral Mesons in External Electromagnetic Field via AdS/CFT · Instability of Gapless Mesons · 0.86
Compares with it 5 papers
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This is in sharp contrast with the zero magnetic field case in which $ℒ=N_c/32πE^2$ is obtained [ref] .
Magnetic instability in AdS/CFT : Schwinger effect and Euler-Heisenberg Lagrangian of Supersymmetric QCD · Magnetic instability and imaginary part of Lagrangian · 0.97
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Consequently, one obtains exactly the same result of the D3/D7 without the $B$ field dual to ordinary SYM [ref] .
Notes on holographic Schwinger effect · Calculation of the decay rate · 0.92
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Likewise, one can observe that in both cases, the curves for $μ=0.673$ are closer to the stationary current curves of [ref] and for large values of the electric field, all currents converge.
Thermal quench of a dynamical QCD model in an external electric field · Stationary current · 1.00
Cites it as background 15 papers
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By adding a probe D8-brane, in [ref] and [ref] the authors studied the imaginary part of the Euler-Heisenberg effective Lagrangian, the rate of pair creation, the critical electric field and the effect of the parallel and perpendicular components of the magnetic field on the rate of pair creation in the background of Sakai-Sugimoto and the deformed Sakai-Sugimoto models.
Schwinger Effect and Entanglement Entropy in Confining Geometries · Introduction · 0.83
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Apparent horizon formation is an interestingly unique procedure that belongs at the heart of AdS/CFT interpretation of thermalization [ref] .
Double Relaxation via AdS/CFT · Review of Holographic Electric Field Quench · 0.84
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Let us first review the physical picture of the instability in the presence of electric field [ref] .
Equilibrium Instability of Chiral Mesons in External Electromagnetic Field via AdS/CFT · Chiral Equilibrium Instability of Quarkonium Mesons · 0.93
What it cites · 19 sentences without a confident label
Uses the method or tool of 1 paper
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The configuration of section 2 provides [equation] The nontrivial $(0,z)$ components of the effective metric $G$ ([ref]) is given as [equation] We can diagonalize this metric by the following field redefinition (see for example a similar transformation in Ref. [ref] ) [equation] to obtain [equation] Substituting ([ref]) and expanding the metric around $z_p$ as $z =z_p + δz$ (here $δz < 0$), [equation] This metric is nothing but a near-horizon metric of a black hole.
Hawking Radiation and Non-equilibrium Quantum Critical Current Noise · The induced metric and the volume · 0.93
Uses data or values from 5 papers
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Let us estimate the induced Planckian time; Formula ([ref]) can be rewritten as ($d=0, η=0$) [equation] The typical field strength realized in RHIC is $E=10^4 [^2]$ [ref] .
The effects of topological charge change in heavy ion collisions: "Event by event P and CP violation" · Planckian thermalization accelerated by electric fields · 0.92
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Let us estimate the induced Planckian time; Formula ([ref]) can be rewritten as ($d=0, η=0$) [equation] The typical field strength realized in RHIC is $E=10^4 [^2]$ [ref] .
Estimate of the magnetic field strength in heavy-ion collisions · Planckian thermalization accelerated by electric fields · 0.92
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Let us estimate the induced Planckian time; Formula ([ref]) can be rewritten as ($d=0, η=0$) [equation] The typical field strength realized in RHIC is $E=10^4 [^2]$ [ref] .
Electromagnetic field evolution in relativistic heavy-ion collisions · Planckian thermalization accelerated by electric fields · 0.92
Cites as background 18 papers
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The quantum quench on the flavor (quark) degrees of freedom has been studied in the context of AdS/CFT [ref] , in addition to the thermalization due to the quantum quench on the bulk gluons (and the spatial volume) in AdS/CFT (see for example Refs. [ref] ).
Inhomogeneous Thermalization in Strongly Coupled Field Theories · Introduction · 0.84
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The quantum quench on the flavor (quark) degrees of freedom has been studied in the context of AdS/CFT [ref] , in addition to the thermalization due to the quantum quench on the bulk gluons (and the spatial volume) in AdS/CFT (see for example Refs. [ref] ).
Holographic Evolution of Entanglement Entropy · Introduction · 0.84
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The quantum quench on the flavor (quark) degrees of freedom has been studied in the context of AdS/CFT [ref] , in addition to the thermalization due to the quantum quench on the bulk gluons (and the spatial volume) in AdS/CFT (see for example Refs. [ref] ).
Instantaneous Thermalization in Holographic Plasmas · Introduction · 0.84
Discussion
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