REVIEW
On the multipole expansion of the gravitational field
General Relativity and Quantum Cosmology · Submitted 29 Jan 1998 · 42 references
Pith's verdict: A solid, foundational methods paper: the all-orders source multipole moments as explicit integrals of the total pseudo-tensor, with the analytic-continuation step as the one load-bearing ingredient that is sketched rather than proved.
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Referee report
The paper
The paper claims
Blanchet derives explicit integral formulas for the gravitational multipole moments of a slowly moving source, valid to all post-Newtonian orders, by integrating the total stress-energy pseudo-tensor with an analytic-continuation weight.
The reading
What carries the argument
The load-bearing device is the finite part at $B=0$ of the $B$-dependent retarded integral, $FP_{B=0} Box_R^{-1}[|y/r_0|^B ...]$, borrowed from the earlier post-Minkowskian construction and now applied to the source's own multipole expansion. Its role is to make sense of integrals whose integrand is not compactly supported, by analytic continuation in the exponent $B$. The pivotal step is the observation that the complete radial integral $int_0^infty d|y| |y/r_0|^B |y|^{2+l+a} (ln|y/r_0|)^p$ vanishes identically for all complex $B$ by analytic continuation, which lets the author move the integration region from an infinitesimal neighbourhood of the origin out to spatial infinity. That jump is what allows the moments to be written as integrals of the post-Newtonian expansion of $tau$ over all space, and it is also why the author flags the result as counterintuitive: the moments formally depend on a post-Newtonian expansion that is only supposed to be valid near the source.
Extended reading notes
Core claim
The central result is equations (3.11)–(3.14): the multipole expansion of the gravitational field outside a slowly moving isolated source equals a finite-part retarded integral of the multipolar gravitational source term plus a sum over multipoles, $M(h^{ij}) = FP_{B=0}[-4G/c^4] + ...$, where each symmetric trace-free moment is an explicit integral of the total stress-energy pseudo-tensor $F^{ij}_L(u) = FP_{B=0} int d^3y |y/r_0|^B y_L int_{-1}^{1} dz delta_l(z) tau^{ij}(y, u + z|y|/c)$. Section V then decomposes the linearized metric into irreducible pieces and extracts six sets of source moments — the mass-type $I_L$, the current-type $J_L$, and four gauge moments $W_L, X_L, Y_L, Z_L$ — as closed integrals over combinations of $tau^{00}, tau^{0i}, tau^{ij}$ (equations 5.15–5.20). The author verifies that in the linearized limit these reduce exactly to the Damour–Iyer expressions, and that at second post-Newtonian order they agree with the earlier matching calculation. The moments so defined parametrize the 'particular' linearized metric that seeds the post-Minkowskian iteration, so the radiation-zone moments follow as nonlinear functionals of them.
Load-bearing premise
The derivation rests on the claim that the full radial integral of the weighted integrand from zero to infinity vanishes identically for every complex value of the continuation parameter, which is what allows the integration region to be moved from the source out to spatial infinity.
Editorial extensions
If this is right
- Every source multipole moment becomes computable from a chosen matter model, so the chain from stress-energy to exterior field to radiated waveform is closed in principle at any post-Newtonian order.
- The linearized-gravity moments of Damour and Iyer, and the second-post-Newtonian moments obtained earlier by asymptotic matching, both fall out as limits, giving a single formula that subsumes the earlier separate derivations.
- Because the four gauge moments $W_L, X_L, Y_L, Z_L$ are also given in closed form, the corrections that first enter at 2.5 post-Newtonian order can be computed rather than inferred.
- The result slots directly into the existing post-Minkowskian iteration, so the tail and other nonlinear corrections to the radiative moments can be carried through without redoing the near-zone analysis.
- The author states the construction should extend to point-particle models of compact objects via regularization, which is the case of practical interest for binary inspiral waveforms.
Reading between the lines
- The construction makes a sharp prediction that can be checked independently: the moments must be independent of the arbitrary length scale $r_0$ introduced by the weight, since it cancels between the two terms of (3.11). A computation that showed residual $r_0$ dependence would indicate the finite-part prescription is incomplete.
- Because the moments are defined by an analytic continuation rather than by a boundary condition at the source, two sources with the same post-Newtonian expansion coefficients but different far-field behaviour would be assigned identical moments; whether that is physically correct is a question the paper does not settle.
- The framework suggests a natural consistency test at third post-Newtonian order: compute $I_L$ and $J_L$ both from these integrals and from an independent near-zone matching, and compare. The author notes third-order work was in preparation, so this comparison is the near-term place where the prescription either holds or does not.
- The reliance on analytic continuation to move an integral from the origin to infinity echoes regularization techniques used elsewhere in classical field theory; if the same identity can be justified by a contour or dimensional-regularization argument, the derivation would no longer rest on a sketched lemma.
Original abstract
This paper constructs the multipole expansion (in general relativity) of the gravitational field generated by a slowly-moving isolated source. We introduce some definitions for the source multipole moments, valid to all orders in a post-Newtonian expansion, and depending in a well-defined way on the total stress-energy pseudo-tensor of the material and gravitational fields. Previously obtained expressions of the source multipole moments are recovered in the appropriate limits. The source moments parametrize the linearized approximation of the gravitational field exterior to the source, as computed by means of a specific post-Minkowskian algorithm defined in a previous work. Since the radiative multipole moments parametrizing the radiation field far from the source can be obtained as non-linear functionals of the source moments, the present paper permits relating the radiation field far from a slowly-moving source to the stress-energy pseudo-tensor of the source. This should be useful when comparing to theory the future observations of gravitational radiation by the LIGO and VIRGO experiments.
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
This paper constructs the multipole expansion (in general relativity) of the gravitational field generated by a slowly-moving isolated source. We introduce some definitions for the source multipole moments, valid to all orders in a post-Newtonian expansion, and depending in a well-defined way on the total stress-energy pseudo-tensor of the material and gravitational fields. Previously obtained expressions of the source multipole moments are recovered in the appropriate limits. The source moments parametrize the linearized approximation of the gravitational field exterior to the source, as computed by means of a specific post-Minkowskian algorithm defined in a previous work. Since the radiative multipole moments parametrizing the radiation field far from the source can be obtained as non-linear functionals of the source moments, the present paper permits relating the radiation field far from a slowly-moving source to the stress-energy pseudo-tensor of the source. This should be useful when comparing to theory the future observations of gravitational radiation by the LIGO and VIRGO experiments.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | This paper constructs the multipole expansion (in general relativity) of the gravitational field generated by a slowly-moving isolated source. | contribution 1.00 | 0.94 | 0.16 | asserted 1.00 |
| s1 | We introduce some definitions for the source multipole moments, valid to all orders in a post-Newtonian expansion, and depending in a well-defined way on the total stress-energy pseudo-tensor of the material and gravitational fields. | contribution 0.86 | 0.94 | 0.08 | asserted 1.00 |
| s2 | Previously obtained expressions of the source multipole moments are recovered in the appropriate limits. | result 0.78 | 0.63 | 0.05 | asserted 1.00 |
| s3 | The source moments parametrize the linearized approximation of the gravitational field exterior to the source, as computed by means of a specific post-Minkowskian algorithm defined in a previous work. | method 0.37 | 0.44 | 0.10 | asserted 1.00 |
| s4 | Since the radiative multipole moments parametrizing the radiation field far from the source can be obtained as non-linear functionals of the source moments, the present paper permits relating the radiation field far from a slowly-moving source to the stress-energy pseudo-tensor of the source. | interpretation 0.76 | 0.58 | 0.53 | asserted 0.84 |
| s5 | This should be useful when comparing to theory the future observations of gravitational radiation by the LIGO and VIRGO experiments. | interpretation 0.58 | 0.08 | 0.08 | hedged possibility 0.82 |
What was examined, and what was not
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References
How the literature uses it
38 arXiv papers cite this in 89 sentences
Papers citing it · 57 sentences without a confident label
Builds on it 1 paper
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The ensuing formulas will generalize the 3-dimensional Eqs. (5.1)-(5.2) in [ref] and the $d$-dimensional ones (3.32)-(3.33) in [ref] .
The current-type quadrupole moment and gravitational-wave mode $(\ell,m)=(2,1)$ of compact binary systems at the third post-Newtonian order · The irreducible decomposition of the multipole expansion · 1.00
Uses its method or tool 15 papers
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In the present paper, we computed the matter stress-energy tensor of the compact binary from the same effective action, and inserted it into a GW generation formalism based on MPM approximations for the external field [ref] , which are matched to the PN expansion of the inner field [ref] .
Tidal effects in the gravitational-wave phase evolution of compact binary systems to next-to-next-to-leading post-Newtonian order · Summary and conclusions · 1.00
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Following the multipolar-post-Minkowskian (MPM) formalism [ref] , we shall express the radiative quadrupole moment $U_ij$ in terms successively of canonical moments ${M_L, S_L}$ and then source moments ${I_L, J_L, W_L, X_L, Y_L, Z_L}$ for general sources at 3.5PN order.
The third and a half post-Newtonian gravitational wave quadrupole mode for quasi-circular inspiralling compact binaries · Expression of the dominant quadrupole mode · 0.97
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In line with Papers I & II, we use the multipolar post-Newtonian approach to gravitational radiation, which combines a multipolar-post-Minkowskian expansion for the vacuum field in the exterior of the matter source [ref] , together with a matching to the post-Newtonian field inside the source [ref] (see Ref. [ref] for a review).
Next-to-leading tail-induced spin-orbit effects in the gravitational radiation flux of compact binaries · Introduction · 0.99
Compares with it 3 papers
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This formalism has exactly the same scope as the one of Refs. [ref] , i.e., it applies to any isolated post-Newtonian sources, but it differs in the definition of the source multipole moments and in many technical details when properly implemented [ref] .
Post-Newtonian Theory for Gravitational Waves · Analytic approximations and wave generation formalism · 0.91
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We contrast and compare these results to the analogous classical derivation of the corrections to the Einstein quadrupole formula using the well-established multipolar post-Minkowskian formalism [ref] .
Scattering Amplitude Techniques in Classical Gauge Theories and Gravity · Introduction · 1.00
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We contrast and compare these results to the analogous classical derivation of the corrections to the Einstein quadrupole formula using the well-established multipolar post-Minkowskian formalism [ref] .
Post-Newtonian Waveforms from Spinning Scattering Amplitudes · Introduction · 0.99
Cites it as background 7 papers
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The symmetric-trace-free (STF) multipole moments of isolated PN radiative sources are known from a matching between the inner PN expansion in the system near zone and the outer MPM expansion in the far zone [ref] .
Tidal effects in the gravitational-wave phase evolution of compact binary systems to next-to-next-to-leading post-Newtonian order · Computation of source multipole moments · 0.88
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These are based on the PN solution of the Einstein equations in the near zone, followed by a matching with the multipole expansion of the gravitational field in the exterior zone and its propagation to the far zone, where it determines the radiative multipoles [ref] (see [ref] for a comprehensive review).
Post-Newtonian Multipoles from the Next-to-Leading Post-Minkowskian Gravitational Waveform · Introduction. · 0.92
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In the multipolar post-Minkowskian (MPM) formalism [ref] , this uniqueness results from the fact that the metric in harmonic coordinates is uniquely determined as the solution of the matching between the MPM metric outside the source and the metric in the near zone, the latter being in the form of a PN expansion [ref] .
Gravitational radiation reaction for compact binary systems at the fourth-and-a-half post-Newtonian order in harmonic coordinates · Introduction · 0.82
Discussion
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