REVIEW 2 major objections 4 minor 1 cited by
Entanglement entropy of linearized gravitons in a sphere
T0 review · 2 major / 4 minor · reviewed 2026-08-14 · deepseek-v4-flash
Pith's one-line read The entanglement entropy of free gravitons in a sphere is that of two free massless scalars with the l=0 and l=1 modes removed, giving a universal logarithmic coefficient of -61/45.
desk verdict New universal log coefficient -61/45 for free gravitons in a sphere, derived from a careful scalar-mode reduction; the main weak point is the l=1 coefficient resting on an undescribed lattice check, but the mutual-information argument and Dowker's independent result make the number credible. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is the decomposition of the metric perturbation $h_{\mu\nu}$ into tensor spherical harmonics, followed by a radial gauge fixing that reduces each angular momentum sector to two independent Hamiltonians of the scalar-spherical form $H = \frac{1}{2}[P^2 + (\partial_r\varphi)^2 + \frac{l(l+1)}{r^2}\varphi^2]$. The gauge parameters are fixed ($\alpha=0$, $\gamma=-\beta/\sqrt{(l-1)(l+2)}$) so that the gauge-fixed fields can be recovered from the linearized curvature tensor by relations with no radial derivatives, ensuring that the operator algebra inside the sphere matches the algebra of gauge-invariant operators. The l=0 and l=1 sectors are then analyzed separately; they drop out of the entropy, so the final answer is two scalar fields with the l=0 and l=1 modes subtracted.
What would settle it
Compute the entanglement entropy of the l=1 scalar Hamiltonian $H=\frac{1}{2}[P^2+(\partial_r\varphi)^2+\frac{2}{r^2}\varphi^2]$ on the half-line $r\in(0,R)$ by exact lattice diagonalization for several lattice spacings; if the coefficient of $\log(R/\epsilon)$ is not $1/6$, the final $-61/45$ shifts by six times the deviation.
Extended reading notes
Core claim
On the paper's own terms, the discovery is that vacuum entanglement of linearized gravitons across a sphere does not need any new machinery beyond the scalar spherical modes: the graviton entropy equals the entropy of two free massless scalars in the same sphere with the l=0 and l=1 sectors subtracted. The l=0 and l=1 graviton modes turn out to be non-dynamical or to cancel, while each l≥2 angular momentum contributes two scalar modes with the usual $\frac{l(l+1)}{r^2}$ potential. Using the known scalar sphere coefficient $-1/90$ and the half-line scalar coefficient $1/6$ for the subtracted modes, the paper obtains $2\times(-1/90) - 2\times(1/6) - 6\times(1/6) = -61/45$ for the coefficient of $\log(R/\epsilon)$. The calculation is done in real time with the gauge-fixed metric perturbation $h_{\mu\nu}$, in a gauge chosen so that the fields inside the sphere generate the same algebra as the curvature tensor localized there.
Load-bearing premise
The load-bearing premise is that the l=1 scalar mode, a one-dimensional field with an inverse-square potential $2/r^2$, has the same logarithmic entropy coefficient $1/6$ as the plain massless scalar; the paper asserts this from dimensional analysis and a lattice check that is not shown in the text.
Editorial extensions
If this is right
- If the calculation is right, the universal logarithmic coefficient for a massless spin-2 field in a sphere in flat space is $-61/45$, independent of the short-distance regulator.
- The graviton sphere entropy is the same as a Maxwell field's entropy with the $l=1$ mode contribution removed, since Maxwell is already two scalars minus the $l=0$ mode.
- The coefficient computed from the entropy coincides with the one obtained from the mutual-information-regulated entropy $S_\epsilon(A)=\frac{1}{2}I(A_+,A_-)$, so the result is insensitive to center-term or edge-mode ambiguities.
- The paper's conjecture for higher helicity $h>2$ is that the coefficient becomes $-(1+15h^2)/45$, from subtracting the $l=0,\dots,h-1$ scalar modes.
- For parallel planes, the graviton entropy reduces to two scalar fields and shares the same universal coefficient as the Maxwell field.
Reading between the lines
- The same gauge-localization logic could be applied to a graviton in a region of arbitrary shape; a natural test is whether non-spherical boundaries change which low angular modes are subtracted, or whether the subtraction pattern is tied to the sphere's symmetry.
- The paper's l=1 scalar mode coefficient $1/6$ could be verified by an independent numerical diagonalization of the one-dimensional Hamiltonian with the $2/r^2$ potential; a deviation would shift every helicity coefficient by six times the error.
- Because the result is regulator-independent and tied to mutual information, it offers a clean benchmark for holographic calculations of graviton entanglement, where the same logarithmic coefficient might be extracted from the dual theory.
- The pattern 'two scalars minus low-l modes' suggests a general rule for free higher-spin fields on the sphere that could be tested mode by mode with the same harmonic decomposition.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This paper computes the entanglement entropy of a massless spin-2 field (linearized gravitons) in a sphere in flat Minkowski space. The authors decompose h_μν in tensor spherical harmonics, fix a gauge adapted to spherical symmetry, and show that for each angular momentum l>=2 the two dynamical modes reduce to two independent scalar spherical modes with the same Hamiltonian as a free massless scalar. They then analyze the low-angular-momentum modes and argue that the entropy is equivalent to that of two free scalars with the l=0 and l=1 modes subtracted. The universal logarithmic coefficient is computed as -61/45, Eq. (5.59), and is argued to agree with the mutual-information regularization.
Significance. If the result holds, this is an important universal coefficient for the entanglement entropy of free gravitons on a sphere, extending the known scalar (-1/90) and Maxwell (-16/45) coefficients to spin 2. The paper's methodological contribution is also significant: it shows how to choose a gauge that preserves the localization of the gauge-invariant algebra inside the sphere, which is essential for interpreting the entropy as a physical quantity. The reduction for l>=2 is explicit and detailed, and the treatment of the l=0 and l=1 modes is a useful step. The paper also gives a concrete prediction that is not fitted to the target value. However, two load-bearing points are not fully supported as written: the logarithmic coefficient of the l=1 scalar mode and the locality relations between the gauge-fixed fields and the curvature tensor.
major comments (2)
- [Section 5.11, Eq. (5.57)] The logarithmic coefficient 1/6 for the l=1 scalar mode is load-bearing for the central result, since Eq. (5.58) subtracts six such modes and the final coefficient -61/45 shifts by 12 delta if the true coefficient is 1/6 + delta. The text justifies (5.57) by scale invariance plus the statement that the UV divergent piece is the same as for a free scalar, and by an undescribed lattice check. Scale invariance alone only fixes the functional form S = a log(R/epsilon) + const; it does not determine a without an independent evaluation of the UV coefficient. The claimed five-digit lattice verification is not described or reproducible. Please provide an explicit derivation of a=1/6 for the Hamiltonian (5.56), or a complete description of the lattice computation and its numerical output, before the final coefficient can be considered established.
- [Section 5.10, Eqs. (5.50)-(5.55)] The claim that the gauge-fixed fields h_{lm}^{1m} and h_l^{te} can be locally expressed in terms of the gauge-invariant curvature inside the sphere is central to identifying the computed entropy with the entropy of the gauge-invariant algebra. The text states that this was obtained by 'computer based algebraic manipulation' but displays explicit angular functions only for m=0, Eqs. (5.51) and (5.55). For general m the locality relations are asserted without explicit formulas or a demonstration from rotational covariance. Please provide the general formulas or a supplementary derivation, since the physical interpretation of the result and the gauge-choice justification rest on this step.
minor comments (4)
- [Section 3] In the sentence 'the model = 0 for the scalar' the intended wording is 'the mode l = 0 for the scalar'; please correct this and similar lapses.
- [Throughout] There are numerous typographical and language issues, including 'studding' (Introduction), 'hT y ξV' (Section 5.3), 'Laplancians' (Appendix A), and 'cames' (Section 6). A thorough English and typographical editing pass is needed.
- [Section 5.11, Eq. (5.57)] The abbreviation 'cons.' for 'constant' is informal; please write 'constant' or define the notation.
- [Section 6] The statement that the UV divergence of the mutual information for the l=0,1 modes 'cannot change due to the potential' is a key step but is only discussed qualitatively; even if a full derivation is deferred, the logic would be clearer if this were expanded into an explicit argument.
Circularity Check
No significant circularity: the graviton entropy result is obtained by reducing the theory to known scalar modes, not by fitting or by self-referential definitions.
full rationale
The derivation chain starts from the linearized metric perturbation and, after a gauge fixing whose locality with the curvature is checked, maps mode I and mode II for each l to standard scalar spherical Hamiltonians (eqs. 5.25 and 5.38) and shows l=0 and l=1 modes drop out (eqs. 5.8, 5.46, 5.49). The final logarithmic coefficient is then assembled by arithmetic from previously established scalar-sphere values: -1/90 per scalar, +1/6 for each subtracted l=0 mode, and +1/6 for each of the 2(2l+1)=6 subtracted l=1 scalar modes (eq. 5.58). None of these inputs is fitted to the target -61/45. The l=1 scalar mode coefficient 1/6 is the only weakly supported input: the text justifies it by the UV divergence being the same as the free scalar after the 2/r^2 potential is neglected, plus scale invariance, and reports an undescribed five-digit lattice check (eq. 5.57). That is a verification gap, not a circular reduction: the coefficient is not defined in terms of the graviton answer and no parameter is fitted to the final number. Self-citations (Casini and Huerta for Maxwell and scalar entropies) refer to independent prior results that do not depend on the target coefficient. Thus no step reduces by construction to its own input; the central claim retains independent content.
Assumptions & free parameters
free parameters (1)
- Gauge-fixing constants α, β, γ
assumptions (5)
- domain assumption Vacuum restricted to a region defines an algebra of operators; entanglement entropy is the entropy of this algebra.
- domain assumption The gauge-fixed variables inside the sphere generate the same algebra as curvature-tensor operators localized there.
- ad hoc to paper The l=1 scalar mode with potential 2/r^2 has logarithmic entropy 1/6.
- domain assumption The mutual information regularization S_epsilon(A) = (1/2) I(A+, A-) equals the entropy used here.
- standard math The sphere log coefficient for a massless scalar is -1/90 and the l=0 scalar mode on the half-line has 1/6.
Cite this review
Pith. "Pith review of Entanglement entropy of linearized gravitons in a sphere." pith.science (2026). https://pith.science/paper/V4VOHWUN
@misc{pith2026190801800,
author = {Pith},
title = {Pith review of: Entanglement entropy of linearized gravitons in a sphere},
year = {2026},
howpublished = {\url{https://pith.science/paper/V4VOHWUN}},
note = {Machine review of arXiv:1908.01800}
}
abstract
We compute the entanglement entropy of a massless spin $2$ field in a sphere in flat Minkowski space. We describe the theory with a linearized metric perturbation field $h_{\mu\nu}$ and decompose it in tensor spherical harmonics. We fix the gauge such that a) the two dynamical modes for each angular momentum decouple and have the dynamics of scalar spherical modes, and b) the gauge-fixed field degrees of freedom inside the sphere represent gauge invariant operators of the theory localized in the same region. In this way the entanglement entropy turns out to be equivalent to the one of a pair of free massless scalars where the contributions of the $l=0$ and $l=1$ modes have been subtracted. The result for the coefficient of the universal logarithmic term is $-61/45$ and coincides with the one computed using the mutual information.
Figures
Forward citations
Cited by 1 Pith paper
-
Note on the entanglement entropy of higher spins in four dimensions
The log coefficient of spherical entanglement entropy for massless higher-spin fields is quadratic in spin, matching and extending the Benedetti-Casini conjecture by extrapolation of low-spin formulas.
Reference graph
Works this paper leans on
-
[1]
Superselection Sectors of Gravitational Subregions
J. Camps, “Superselection Sectors of Gravitational Subregions,” JHEP1901, 182 (2019) [arXiv:1810.01802 [hep-th]]
work page Pith review arXiv 2019
-
[2]
W. Donnelly and S. B. Giddings, Phys. Rev. D96, 086013 (2017) [arXiv:1706.03104 [hep-th]]
arXiv 2017
-
[3]
Holographic derivation of entanglement entropy from AdS/CFT,
S. Ryu and T. Takayanagi, “Holographic derivation of entanglement entropy from AdS/CFT,” Phys. Rev. Lett.96, 181602 (2006) [hep-th/0603001]
arXiv 2006
-
[4]
Quantum corrections to holographic entanglement entropy,
T. Faulkner, A. Lewkowycz and J. Maldacena, “Quantum corrections to holographic entanglement entropy,” JHEP1311, 074 (2013) [arXiv:1307.2892 [hep-th]]
arXiv 2013
-
[5]
The Gravity Dual of a Density Matrix,
B. Czech, J. L. Karczmarek, F. Nogueira and M. Van Raamsdonk, “The Gravity Dual of a Density Matrix,” Class. Quant. Grav.29, 155009 (2012) [arXiv:1204.1330 [hep-th]]
arXiv 2012
-
[6]
Relative entropy equals bulk relative entropy,
D. L. Jafferis, A. Lewkowycz, J. Maldacena and S. J. Suh, “Relative entropy equals bulk relative entropy,” JHEP1606, 004 (2016) [arXiv:1512.06431 [hep-th]]
arXiv 2016
-
[7]
Reconstruction of Bulk Operators within the Entanglement Wedge in Gauge-Gravity Duality,
X. Dong, D. Harlow and A. C. Wall, “Reconstruction of Bulk Operators within the Entanglement Wedge in Gauge-Gravity Duality,” Phys. Rev. Lett.117, no. 2, 021601 (2016) [arXiv:1601.05416 [hep-th]]
arXiv 2016
-
[8]
Entanglement entropy of black holes,
S. N. Solodukhin, “Entanglement entropy of black holes,” Living Rev. Rel.14, 8 (2011) [arXiv:1104.3712 [hep-th]]
arXiv 2011
Show all 38 references
-
[9]
Logarithmic Corrections to Schwarzschild and Other Non-extremal Black Hole Entropy in Different Dimensions,
A. Sen, “Logarithmic Corrections to Schwarzschild and Other Non-extremal Black Hole Entropy in Different Dimensions,” JHEP1304, 156 (2013) [arXiv:1205.0971 [hep-th]]
2013 arXiv
-
[10]
Entanglement entropy of a Maxwell field on the sphere,
H. Casini and M. Huerta, “Entanglement entropy of a Maxwell field on the sphere,” Phys. Rev. D93, no. 10, 105031 (2016) [arXiv:1512.06182 [hep-th]]
2016 arXiv
-
[11]
Entanglement entropy for even spheres,
J. S. Dowker, “Entanglement entropy for even spheres,” arXiv:1009.3854 [hep-th]
-
[12]
Central Charge and Entangled Gauge Fields,
K. W. Huang, “Central Charge and Entangled Gauge Fields,” Phys. Rev. D92, no. 2, 025010 (2015) doi:10.1103/PhysRevD.92.025010 [arXiv:1412.2730 [hep-th]]
2015 arXiv
-
[13]
Entanglement entropy and super- selection sectors I. Global symmetries,
H. Casini, M. Huerta, J. M. Magán and D. Pontello, “Entanglement entropy and super- selection sectors I. Global symmetries,” arXiv:1905.10487 [hep-th]
1905 arXiv
-
[14]
On the logarithmic coefficient of the entanglement entropy of a Maxwell field,
H. Casini, M. Huerta, J. M. Magán and D. Pontello, “On the logarithmic coefficient of the entanglement entropy of a Maxwell field,” to appear
-
[15]
Geometric entropy and edge modes of the electromagnetic field,
W. Donnelly and A. C. Wall, “Geometric entropy and edge modes of the electromagnetic field,” Phys. Rev. D94, no. 10, 104053 (2016) [arXiv:1506.05792 [hep-th]]. 28
2016 arXiv
-
[16]
On The Entanglement Entropy For Gauge Theories,
S. Ghosh, R. M. Soni and S. P. Trivedi, “On The Entanglement Entropy For Gauge Theories,” JHEP1509, 069 (2015) [arXiv:1501.02593 [hep-th]]
2015 arXiv
-
[17]
Remarks on entanglement entropy for gauge fields,
H. Casini, M. Huerta and J. A. Rosabal, “Remarks on entanglement entropy for gauge fields,” Phys. Rev. D89, no. 8, 085012 (2014) [arXiv:1312.1183 [hep-th]]
2014 arXiv
-
[18]
Entanglement and alpha entropies for a massive scalar field in two dimensions,
H. Casini and M. Huerta, “Entanglement and alpha entropies for a massive scalar field in two dimensions,” J. Stat. Mech.0512, P12012 (2005) [cond-mat/0511014]
2005 arXiv
-
[19]
Entanglement entropy in free quantum field theory,
H. Casini and M. Huerta, “Entanglement entropy in free quantum field theory,” J. Phys. A 42, 504007 (2009) [arXiv:0905.2562 [hep-th]]
2009 arXiv
-
[20]
Entropy and area,
M. Srednicki, “Entropy and area,” Phys. Rev. Lett.71, 666 (1993) [hep-th/9303048]
1993 arXiv
-
[21]
Entanglement entropy, conformal invariance and extrinsic geometry,
S. N. Solodukhin, “Entanglement entropy, conformal invariance and extrinsic geometry,” Phys. Lett. B665, 305 (2008) [arXiv:0802.3117 [hep-th]]
2008 arXiv
-
[22]
Entanglement entropy for the n-sphere,
H. Casini and M. Huerta, “Entanglement entropy for the n-sphere,” Phys. Lett. B694, 167 (2011) [arXiv:1007.1813 [hep-th]]
2011 arXiv
-
[23]
Towards a derivation of holographic entangle- ment entropy,
H. Casini, M. Huerta and R. C. Myers, “Towards a derivation of holographic entangle- ment entropy,” JHEP1105, 036 (2011) [arXiv:1102.0440 [hep-th]]
2011 arXiv
-
[24]
Numerical determination of entanglement entropy for a sphere,
R. Lohmayer, H. Neuberger, A. Schwimmer and S. Theisen, “Numerical determination of entanglement entropy for a sphere,” Phys. Lett. B685, 222 (2010) [arXiv:0911.4283 [hep-lat]]
2010 arXiv
-
[25]
Entanglement entropy and quantum field theory,
P. Calabrese and J. L. Cardy, “Entanglement entropy and quantum field theory,” J. Stat. Mech.0406, P06002 (2004) [hep-th/0405152]
2004 arXiv
- [26]
-
[27]
Gravitation,
C. W. Misner, K. S. Thorne and J. A. Wheeler, “Gravitation,” W. H. Freeman and Company, San Francisco 1973, 1279p
1973
-
[28]
Gravitational multipole moments from Noether charges,
G. Compère, R. Oliveri and A. Seraj, “Gravitational multipole moments from Noether charges,” JHEP1805, 054 (2018) [arXiv:1711.08806 [hep-th]]
2018 arXiv
-
[29]
Multipole Expansions of Gravitational Radiation,
K. S. Thorne, “Multipole Expansions of Gravitational Radiation,” Rev. Mod. Phys.52, 299 (1980)
1980
-
[30]
Stability of a Schwarzschild singularity,
T. Regge and J. A. Wheeler, “Stability of a Schwarzschild singularity,” Phys. Rev.108, 1063 (1957)
1957
-
[31]
Mutual information and the F- theorem,
H. Casini, M. Huerta, R. C. Myers and A. Yale, “Mutual information and the F- theorem,” JHEP1510, 003 (2015) [arXiv:1506.06195 [hep-th]]. 29
2015 arXiv
-
[32]
Entropy and modular Hamilto- nian for a free chiral scalar in two intervals,
R. E. Arias, H. Casini, M. Huerta and D. Pontello, “Entropy and modular Hamilto- nian for a free chiral scalar in two intervals,” Phys. Rev. D98, no. 12, 125008 (2018) [arXiv:1809.00026 [hep-th]]
2018 arXiv
-
[33]
Cones, spins and heat kernels,
D. V. Fursaev and G. Miele, “Cones, spins and heat kernels,” Nucl. Phys. B484, 697 (1997) [hep-th/9605153]
1997 arXiv
-
[34]
Newton constant, contact terms and entropy,
S. N. Solodukhin, “Newton constant, contact terms and entropy,” Phys. Rev. D91, no. 8, 084028 (2015) [arXiv:1502.03758 [hep-th]]
2015 arXiv
-
[35]
Limits on Massless Particles,
S. Weinberg and E. Witten, “Limits on Massless Particles,” Phys. Lett.96B, 59 (1980)
1980
-
[36]
One loop quantum gravity on de Sitter space,
D. V. Vassilevich, “One loop quantum gravity on de Sitter space,” Int. J. Mod. Phys. A 8, 1637 (1993). doi:10.1142/S0217751X93000679
1993 doi
-
[37]
The Parts of the Gravitational Field,
J. Camps, “The Parts of the Gravitational Field,” arXiv:1905.10121 [hep-th]
1905 arXiv
-
[38]
Note on the entanglement entropy of higher spins in four dimensions,
J. S. Dowker, “Note on the entanglement entropy of higher spins in four dimensions,” arXiv:1908.04870 [hep-th]. 30
1908 arXiv
Reviewed August 14, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.