REVIEW
The Einstein Equations on the 3-Brane World
General Relativity and Quantum Cosmology · Submitted 22 Oct 1999 · 20 references
Pith's verdict: The paper that gave brane-world cosmology its working Einstein equations; the derivation holds, and the RS1 exclusion is stronger than the stress-test allows, though the abstract states it more absolutely than the body does.
T0 · AI review
Why Pith says this
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Referee report
The paper
The paper claims
The gravitational equations that a brane-world observer would actually measure are derived, and they rule out the negative-tension brane.
The reading
What carries the argument
The engine is the pair of embedding identities — the Gauss equation relating the brane's Riemann tensor to the bulk Riemann tensor plus extrinsic curvature, and the Codazzi equation relating the divergence of the extrinsic curvature to the bulk Ricci tensor contracted with the normal — combined with Israel's junction condition across the brane and a $Z_2$ reflection symmetry that makes the extrinsic curvature on the two sides equal and opposite. That mirror symmetry is what turns a jump condition into an algebraic formula for $K_{mu nu}$ in terms of the brane stress-energy, and it is that formula which, fed back into the Gauss equation, produces the effective four-dimensional Einstein equations. The final equation's structure is worth naming: $8pi G_N tau_{mu nu}$ is ordinary matter, $kappa_5^4 pi_{mu nu}$ is a high-energy correction quadratic in the stress-energy, and $E_{mu nu}$ is the imprint of the bulk gravitational field, traceless and constrained in divergence but not in transverse-traceless part.
Extended reading notes
Core claim
Starting from the Gauss equation, the Codazzi equation, and the decomposition of the five-dimensional Riemann tensor into Weyl, Ricci, and scalar parts, the authors obtain the induced four-dimensional Einstein tensor on a hypersurface without assuming any symmetry. They then specialise to the brane-world setting: a five-dimensional stress-energy tensor of the form $T_{ab} = -Lambda g_{ab} + S_{ab} delta(chi)$ with $S_{mu nu} = -lambda q_{mu nu} + tau_{mu nu}$, Israel's junction condition $[K_{mu nu}] = -kappa_5^2 (S_{mu nu} - q_{mu nu} S/3)$, and $Z_2$ symmetry about the brane. The junction condition then fixes the extrinsic curvature algebraically, $K_{mu nu} = -kappa_5^2(S_{mu nu} - q_{mu nu}S/3)/2$, and substituting this back yields the central result: $^{(4)}G_{mu nu} = -Lambda_4 q_{mu nu} + 8 pi G_N tau_{mu nu} + kappa_5^4 pi_{mu nu} - E_{mu nu}$, with $Lambda_4 = kappa_5^2(Lambda + kappa_5^2 lambda^2/6)/2$, $G_N = kappa_5^4 lambda / 48 pi$, $pi_{mu nu}$ a specific quadratic expression in $tau$, and $E_{mu nu}$ the electric part of the five-dimensional Weyl tensor evaluated at the brane. Because the sign of $G_N$ tracks the sign of $lambda$, the negative-tension brane of the first Randall–Sundrum scenario is an anti-gravity world and the authors reject it, while the positive-tension second scenario gives ordinary attraction. The same equation, combined with the contracted Bianchi identity, gives $D^mu E_{mu nu} = kappa_5^4[tau^{alpha beta}(D_nu tau_{alpha beta} - D_beta tau_{nu alpha}) + (tau_{mu nu} - q_{mu nu}tau) D^mu tau/3]/4$, so the Weyl term is not free but sourced by matter; setting $E_{mu nu} = 0$ for an exactly anti-de Sitter bulk and taking a perfect fluid forces $partial_i rho = 0$, i.e. spatial homogeneity.
Load-bearing premise
Everything rests on splitting the brane's stress-energy into a constant vacuum tension plus ordinary matter, $S_{mu nu} = -lambda q_{mu nu} + tau_{mu nu}$, with $lambda$ a well-defined number — and the authors themselves note this split is ambiguous, particularly in cosmology, and that Newton's constant becomes undefinable when the distinction between vacuum and matter energy blurs.
Editorial extensions
If this is right
- Newton's constant on the brane is fixed by the brane tension, $G_N = kappa_5^4 lambda/48pi$, so a brane with negative tension has a gravitational coupling of the wrong sign and cannot host ordinary attractive gravity.
- The first Randall–Sundrum scenario, whose visible brane carries negative tension, is excluded on physical grounds; the second, positive-tension scenario survives and recovers four-dimensional Einstein gravity at low energies.
- In a strictly anti-de Sitter bulk, the vanishing of the projected Weyl tensor plus the four-dimensional Bianchi identity forces a perfect fluid on the brane to be spatially homogeneous, so inhomogeneous matter requires the bulk to deviate from exact anti-de Sitter.
- The quadratic term $pi_{mu nu}$ grows relative to the linear matter term as the square of the energy scale, so it matters in the early universe and is negligible today.
- The effective equations stop being meaningful in any era where the split between vacuum energy and ordinary matter on the brane is ill-defined, such as when a scalar field's potential energy dominates.
Reading between the lines
- The paper's sign argument turns brane tension into a selection principle rather than a free parameter, which suggests that any brane-world model builder should treat the sign of the tension as a consistency check before doing cosmology.
- Because $E_{mu nu}$ carries the transverse-traceless part that is not fixed by brane matter, brane observers are in principle able to infer something about the bulk geometry from gravitational-wave data alone; the bulk is not sealed off from brane measurement.
- The acknowledged ambiguity in separating $lambda$ from $tau_{mu nu}$ is sharpest precisely during inflation, so the framework's most-wanted application and its weakest point coincide; a treatment that absorbs the scalar potential into an effective, time-dependent tension would be the natural next step.
- The homogeneity constraint in the exact anti-de Sitter case suggests a diagnostic: any brane-world cosmology with structure must come with a non-zero Weyl contribution, so the size of that contribution is a bookkeeping entry for how much bulk gravity the model is secretly importing.
Original abstract
We carefully investigate the gravitational equations of the brane world, in which all the matter forces except gravity are confined on the 3-brane in a 5-dimensional spacetime with $Z_2$ symmetry. We derive the effective gravitational equations on the brane, which reduce to the conventional Einstein equations in the low energy limit. {}From our general argument we conclude that the first Randall & Sundrum-type theory (RS1) [hep-ph/9905221] predicts that the brane with the negative tension is an anti-gravity world and hence should be excluded from the physical point of view. Their second-type theory (RS2) [hep-th/9906064] where the brane has the positive tension provides the correct signature of gravity. In this latter case, if the bulk spacetime is exactly anti-de Sitter, generically the matter on the brane is required to be spatially homogeneous because of the Bianchi identities. By allowing deviations from anti-de Sitter in the bulk, the situation will be relaxed and the Bianchi identities give just the relation between the Weyl tensor and the energy momentum tensor. In the present brane world scenario, the effective Einstein equations cease to be valid during an era when the cosmological constant on the brane is not well-defined, such as in the case of the matter dominated by the potential energy of the scalar field.
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 carefully investigate the gravitational equations of the brane world, in which all the matter forces except gravity are confined on the 3-brane in a 5-dimensional spacetime with $Z_2$ symmetry. We derive the effective gravitational equations on the brane, which reduce to the conventional Einstein equations in the low energy limit. {}From our general argument we conclude that the first Randall & Sundrum-type theory (RS1) [hep-ph/9905221] predicts that the brane with the negative tension is an anti-gravity world and hence should be excluded from the physical point of view. Their second-type theory (RS2) [hep-th/9906064] where the brane has the positive tension provides the correct signature of gravity. In this latter case, if the bulk spacetime is exactly anti-de Sitter, generically the matter on the brane is required to be spatially homogeneous because of the Bianchi identities. By allowing deviations from anti-de Sitter in the bulk, the situation will be relaxed and the Bianchi identities give just the relation between the Weyl tensor and the energy momentum tensor. In the present brane world scenario, the effective Einstein equations cease to be valid during an era when the cosmological constant on the brane is not well-defined, such as in the case of the matter dominated by the potential energy of the scalar field.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We carefully investigate the gravitational equations of the brane world, in which all the matter forces except gravity are confined on the 3-brane in a 5-dimensional spacetime with $Z_2$ symmetry. | contribution 0.70 | 0.88 | 0.04 | asserted 0.91 |
| s1 | We derive the effective gravitational equations on the brane, which reduce to the conventional Einstein equations in the low energy limit. {}From our general argument we conclude that the first Randall & Sundrum-type theory (RS1) [hep-ph/9905221] predicts that the brane with the negative tension is an anti-gravity world and hence should be excluded from the physical point of view. | result 0.75 | 0.90 | 0.55 | asserted 0.99 |
| s2 | Their second-type theory (RS2) [hep-th/9906064] where the brane has the positive tension provides the correct signature of gravity. | result 0.78 | 0.43 | 0.13 | asserted 1.00 |
| s3 | In this latter case, if the bulk spacetime is exactly anti-de Sitter, generically the matter on the brane is required to be spatially homogeneous because of the Bianchi identities. | result 0.95 | 0.68 | 0.07 | asserted 1.00 |
| s4 | By allowing deviations from anti-de Sitter in the bulk, the situation will be relaxed and the Bianchi identities give just the relation between the Weyl tensor and the energy momentum tensor. | result 0.86 | 0.75 | 0.08 | asserted 0.94 |
| s5 | In the present brane world scenario, the effective Einstein equations cease to be valid during an era when the cosmological constant on the brane is not well-defined, such as in the case of the matter dominated by the potential energy of the scalar field. | limitation 0.56 | 0.74 | 0.10 | asserted 0.99 |
What was examined, and what was not
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References
How later papers used it
240 later papers cite it
18 later papers by other authors are listed below: 1 built on it and 17 used its method or tool. 1 more paper by the same authors is listed: 1 used its method or tool.
Builds on it 1 of 3 papers with this label
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Found the (4+n)-dimensional generalization of this paper's equations using its junction conditions.
Kaluza-Klein brane cosmology with a bulk scalar field (2011) · 0.98 · paraphrased: the licence does not allow quoting
Uses its method or tool 18 of 39 papers with this label · 1 by the same authors
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Used the effective gravitational field equations derived by this paper.
Wormholes in de Sitter branes (2012) · 1.00 · paraphrased: the licence does not allow quoting
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Involved the gravity on the brane using the method provided in this paper, with the brane evolution determined by the effective Einstein field equation on the brane and the Israel junction condition together.
Brane universe and holography in spacetime of charged AdS dilaton black hole (2019) · 1.00 · paraphrased: the licence does not allow quoting
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Wrote down the effective gravitational equations on the brane by means of the covariant decomposition developed by this paper.
Anisotropic fluid from nonlocal tidal effects (2014) · 1.00 · paraphrased: the licence does not allow quoting
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Used this paper's recipe to find the brane-world stress tensor satisfying the equation of state ρ = -p = const. < 0, giving an AdS-type brane metric.
Negative $\Lambda$ induced by accelerated motion (2014) · 1.00 · paraphrased: the licence does not allow quoting
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Used this paper's formalism, employing the Gauss-Codazzi equations and Israel-Darmois junction conditions to project the five-dimensional curvature along the brane.
Cosmological accretion onto braneworld black holes: a relativistic treatment (2026) · 1.00 · paraphrased: the licence does not allow quoting
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Obtained the effective Einstein equation on the brane following the approach introduced by this paper.
Self-accelerating the normal DGP branch (2009) · 1.00 · paraphrased: the licence does not allow quoting
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Wrote down the effective gravitational equations on the brane by means of the covariant decomposition developed by this paper.
Regular Schwarzschild-like spacetime embedded in a five dimensional bulk (2021) · 1.00 · paraphrased: the licence does not allow quoting
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Used this paper's formalism, in which gravitational phenomena in a brane immersed in a five-dimensional bulk are described by effective four-dimensional Einstein equations.
Black holes and wormholes in AdS branes (2010) · 0.99 · paraphrased: the licence does not allow quoting
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Following the approach suggested by this paper, wrote the effective four-dimensional gravitational field equations in a vacuum Randall-Sundrum brane.
Electromagnetic perturbations in new brane world scenarios (2016) · 0.99 · paraphrased: the licence does not allow quoting
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Summarized the 5D action and equations in the formalism developed by this paper.
Holography for the Trace Anomaly Action (2023) · 0.98 · paraphrased: the licence does not allow quoting
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Following many brane-world scenarios including this paper, wrote the brane energy-momentum tensor with brane tension λ and matter tensor τ_μν.
Wormholes from beyond (2024) · 0.83 · paraphrased: the licence does not allow quoting
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Used the equations above, which were used to develop a covariant analysis of the weak field in this paper, to develop a Taylor expansion of the metric along the extra dimension predicting the black string behavior.
Black string corrections in variable tension braneworld scenarios (2012) · 0.82 · paraphrased: the licence does not allow quoting
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The effective 4D Einstein equation seen by a brane observer is computed from the 5D Einstein equation by projecting on the brane via the Gauss equation together with the Israel junction condition [ref] .
Cosmological Dark Matter from a Bulk Black Hole (2022) · The 5D scalar-gravity system · 0.95
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Following this paper, wrote 5-dimensional Einstein equations with a bulk cosmological constant and brane energy-momentum as source.
A New Fate of a Warped 5D FRW Model with a U(1) Scalar Gauge Field (2015) · 0.89 · paraphrased: the licence does not allow quoting
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Using this paper's procedure, gave the field equations on the brane with brane tension λ, energy momentum tensor τ_μν, π_μν, and the electric part of the Weyl tensor.
Brane-$f(R)$ gravity and dark matter (2012) · 0.81 · paraphrased: the licence does not allow quoting
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Used the Israel junction conditions and the Gauss-Codazzi equations, as employed by this paper, in obtaining the field equations on the brane.
Anisotropy in Born-Infeld brane cosmology (2011) · 0.96 · paraphrased: the licence does not allow quoting
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Following this paper's derivation, wrote the induced Einstein equations on the brane with a 4-dimensional cosmological constant, κ, S_μν, ℱ_μν, and ξ_μν.
Relativistic Images in Randall-Sundrum II Braneworld Lensing (2009) · 0.87 · paraphrased: the licence does not allow quoting
By the same authors
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Used this paper's equation to analyze the Kaluza-Klein cosmology.
Kaluza-Klein braneworld cosmology with static internal dimensions (2007) (same authors) · 1.00 · paraphrased: the licence does not allow quoting
How the literature uses it
219 arXiv papers cite this in 394 sentences
Papers citing it · 259 sentences without a confident label
Builds on it 3 papers
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Using this junction conditions, we find the $(4+n)$-dimensional generalization of the Shiromizu-Maeda-Sasaki equations [ref] ,
Kaluza-Klein brane cosmology with a bulk scalar field · Action and field equations · 0.98
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Building on the framework of Refs. [ref] , one can incorporate matter on the brane—here, an Einstein cluster—into the effective four-dimensional field equations [ref] and investigate its impact on both the matter distribution and the resulting spacetime geometry.
Astrophysical environment around a black hole in the braneworld and its optical signatures · Introduction · 0.97
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This approach has been previously used [ref] - [ref] in brane scenarios and now we apply it to the case of brane vectors.
Brane Vector Dynamics from Embedding Geometry · Embedding geometry and Einstein equation on brane · 0.89
Uses its method or tool 37 papers
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Within the braneworld scenario, the field equations induced on the brane are derived via an elegant geometric approach developed in Ref. [ref] .
Mass radius relation of compact stars in the braneworld · Tolman-Oppenheimer-Volkoff Equations in the braneworld · 0.87
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Following Nakas and Kanti [ref] , the total energy-momentum tensor could be written as [equation] where the delta $δ(y)$ asks for a junction condition, and the brane energy-momentum tensor, following many brane-world scenarios [ref] , is given by [equation] The constant $λ$ is the brane tension, which is some sort of vacuum energy on the brane, and the tensor $τ_μν$ represents all matter fields or sources exclusively on the brane.
Wormholes from beyond · The brane equations · 0.83
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We used the effective gravitational field equations derived by Shiromizu, Maeda, and Sasaki [ref] .
Wormholes in de Sitter branes · Introduction · 1.00
Compares with it 8 papers
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The main result of this paper is the existence of the trace part of the brane energy-momentum tensor in the modified Einstein equations on the brane, which is a modification of the SMS effective equation [ref] .
Modified Gravitational Equations on Braneworld with Lorentz Invariant Violation · Conclusions · 0.80
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For low energy density, $GL^2ρ≪1$ and $L^2 C/a^4≪1$, in the approximation beyond the leading order, cf. Eq.([ref]), this equation reads[We assume that the dark radiation term is redshifted for growing $a$ faster than matter term and expand to the second order in $ρ$, but the first order in $C$.] [equation] and coincides with the modified Friedmann equation in the Randall-Sundrum model [ref] [equation] where $σ=3/8πG_5L=3/4πGL^2$ is the Randal-Sundrum brane tension and $C$ is the braneworld constant of motion [ref] .
Anomaly Driven Cosmology: Big Boost Scenario and AdS/CFT Correspondence · AdS/CFT and Randall-Sundrum braneworld setup · 0.91
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For low energy density, $GL^2ρ≪1$ and $L^2 C/a^4≪1$, in the approximation beyond the leading order, cf. Eq.([ref]), the modified Friedmann equation coincides with the modified Friedmann equation in the Randall-Sundrum model [ref] [equation] where $σ=3/8πG_5L=3/4πGL^2$ is the Randall-Sundrum brane tension and $C$ is the braneworld constant of motion [ref] .[We assume that the dark radiation term is redshifted, as $a$ grows, faster than the matter term and expand to the second order in $ρ$, but the first order in $C$.] Note that the thermal radiation on the brane (of non-Casimir energy nature) is equivalent to the mass of the bulk black hole associated with this constant.
Density matrix of the Universe reloaded: origin of inflation and cosmological acceleration · Dual description via the AdS/CFT correspondence · 0.91
Cites it as support 1 paper
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However, this problem can be avoided if our universe is confined on the positive tension brane [ref] .
Gravity localization and mass hierarchy in scalar-tensor branes · I. Introduction · 0.98
Cites it as background 74 papers
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The effective 3+1 dimensional Einstein field equations on the brane for the Randall and Sundrum model were derived by Shiromizu, Maeda, and Sasaki [ref] .
Gravitational Geons on the Brane · Introduction · 0.93
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In the 5D warped space models involving a non-compact extra dimension, the gravitational field equations in the bulk can be expressed in the form [ref] [equation] where the fundamental 5D Planck mass $M_P$ enters via $k^2=8π/M_P^3$, $λ$ is the brane tension, and $Λ$ is the bulk cosmological constant.
Quasiperiodic oscillations in a strong gravitational field around neutron stars testing braneworld models · Gravitational field equations on the brane and the exterior spacetime to the uniform density configurations · 0.90
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According to the general formulation of SMS braneworld scenario [ref] , our $4D$ universe (the brane) is embedded locally and isometrically in a codimension-1 ambient (the bulk) space, in which the standard model fields are confined to the brane, while gravity propagates in all spatial dimensions.
Intrinsic quantum dynamics of particles in brane gravity · Newtonian dynamics of particles · 0.95
Discussion
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