REVIEW 2 major objections 4 minor 25 references
Fill-Ins of Tori with Scalar Curvature Bounded from Below
T0 review · 2 major / 4 minor · reviewed 2026-08-12 · deepseek-v4-flash
Pith's one-line read For flat tori $S^1 \times T^{n-2}$ with $3 \le n \le 7$, fill-ins with scalar curvature $\ge -n(n-1)$ and positive mean curvature obey a sharp total-mean-curvature bound whose constant is attained in the limit.
desk verdict The flat-torus sharp estimate in Theorem 1.6 is likely correct and worth refereeing, but the advertised general torus-boundary result (Theorem 1.8) is not proven as written because the final rescaling step in the proof of Theorem 1.7 changes the prescribed boundary metric. 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 prescribed scalar curvature equation on the hyperbolic cylinder $\Sigma \times [\rho_0, \infty)$ with metric $g = \rho^2\gamma + u^2\rho^{-2}d\rho^2$; the scalar-curvature condition $R_g = -n(n-1)$ reduces to $(n-1)\rho\,\partial_\rho u = u^2\Delta_{\Sigma_\rho}u - \frac{1}{2}n(n-1)(u^3-u)$. Solving this equation with boundary data coming from the fill-in yields the asymptotic expansion $u = 1 + \mu(x)\rho^{-n} + O(\rho^{-n-2})$. A perturbation of the level sets of $\rho$ by a function that solves a Laplacian equation adjusts the mean curvature of a large torus slice to the desired constant. A gluing lemma attaches this cylinder to the fill-in while nearly preserving the lower scalar-curvature bound, and a systolic inequality on the torus converts any mean-curvature excess into a contradiction unless the claimed estimate holds.
What would settle it
Produce a fill-in of a flat metric $\gamma$ on $S^1 \times T^{n-2}$ with $R_g \ge -n(n-1)$ and $H_{\Sigma} > 0$ for which the normalized total mean curvature exceeds $\frac{1}{2}\left(\frac{4\pi}{n\sigma}\right)^n$; a numerical construction in the allowed dimensions would disprove the sharp estimate. Separately, check the rescaling step in the interpolation theorem: for any glued metric $g'$ with boundary $\gamma$, a global rescaling $c^2g'$ has boundary $c^2\gamma$, so preserving the boundary metric forces $c=1$; verifying whether a different deformation can raise the scalar-curvature lower bound to $-n(n-1)$ would decide whether the arbitrary-boundary theorem stands.
Extended reading notes
Core claim
The central claim is Theorem 1.6: if $\gamma$ is flat on $\Sigma$, $g$ fills $\Omega = B^2 \times T^{n-2}$, $R_g \ge -n(n-1)$, $g|_{\partial\Omega} = \gamma$, and $H_{\Sigma} > 0$, then $\frac{1}{\mathrm{vol}(\Sigma)} \int_{\Sigma} (H_{\Sigma} - (n-1))\, d\mathrm{vol}_{\gamma} \le \frac{1}{2} \left(\frac{4\pi}{n\sigma}\right)^n$, where $\sigma$ is the length of the shortest closed curve in $\Sigma$ whose integral of $\Xi$ is nonzero, and $\Xi$ is the pullback of the volume form on the circle factor. The constant is sharp: taking larger and larger pieces of the model metrics on $\mathbb{R}^2 \times T^{n-2}$ makes the left-hand side approach the bound. The paper also proves an interpolation theorem comparing different boundary metrics and uses it to obtain a uniform total-mean-curvature bound for arbitrary boundary metrics on the same torus.
Load-bearing premise
The proof of the interpolation theorem ends by asserting that the glued metric can be rescaled so its scalar curvature is at least $-n(n-1)$, but a constant rescaling changes the boundary metric from $\gamma$ to $c^2\gamma$, so that step is not justified as written; if it cannot be repaired, the uniform bound for arbitrary boundary metrics does not follow.
Editorial extensions
If this is right
- The sharp estimate settles the flat-torus case of the total-mean-curvature conjecture for fill-ins with scalar curvature bounded below.
- For any boundary metric on $S^1 \times T^{n-2}$, the interpolation theorem yields a constant $C = C(n, \gamma)$ such that every admissible fill-in has $\int_{\partial\Omega} H\, d\mathrm{vol} \le C$.
- The constant in the flat case is optimal, approached by the model metrics on $\mathbb{R}^2 \times T^{n-2}$ filling larger tori.
- The proof demonstrates that the systolic inequality can replace the positive mass theorem in deriving total-mean-curvature estimates in this setting.
Reading between the lines
- A direct proof via a positive mass theorem may be possible; the paper notes it used the systolic inequality instead, so recovering the same constant from a mass inequality would likely extend the result beyond the dimension range allowed by the gluing construction.
- The interpolation mechanism suggests a route to sharp constants for non-flat boundary metrics: compare any boundary metric with a flat one, so the flat constant may control the whole conformal class up to a geometric factor.
- The construction is testable numerically for small $n$: a sequence of fill-ins approaching the bound should develop a long cylindrical neck whose length is controlled by the systolic length $\sigma$ of the boundary torus.
- The dimension restriction $3 \le n \le 7$ appears to come from the gluing lemma, so a different gluing argument is a natural route to higher-dimensional analogues.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper studies fill-ins of the torus Σ = S^1 × T^{n-2} (3 ≤ n ≤ 7) with scalar curvature bounded below by -n(n-1). Theorem 1.6 establishes, for flat boundary metrics γ, a sharp upper bound on the total mean curvature of the boundary, with the constant expressed in terms of the systolic length σ; sharpness is claimed via Horowitz–Myers metrics. Theorem 1.7 is an interpolation result: from a fill-in of a smaller metric γ̂ one constructs a fill-in of a larger metric γ with controlled total mean curvature. Theorem 1.8 then derives a general total-mean-curvature bound for arbitrary boundary metrics by combining Theorems 1.6 and 1.7. The proofs use the prescribed scalar curvature equation, a priori estimates, a gluing construction, and the Brendle–Hung systolic inequality.
Significance. If correct, Theorem 1.6 resolves a special case of Gromov's conjecture on total mean curvature for fill-ins with scalar curvature bounded below, in the setting of flat tori, and provides a sharp constant. The use of the Brendle–Hung systolic inequality in place of a direct positive mass argument is a genuine novelty. The paper also gives a route toward general boundary metrics via Theorem 1.8. The arguments are largely coherent, and the dependence on machine-checkable or previously established estimates (parabolic a priori estimates, gluing lemmas) is explicit. However, two issues affect the proofs as written: a typo in the final inequality of Theorem 1.6, and a more substantial gap in the rescaling step of Theorem 1.7.
major comments (2)
- [Section 3, Proof of Theorem 1.7, last paragraph] The assertion 'Finally, we can rescale g so that the scalar curvature is bounded from below by -n(n-1)' is not justified. A global rescaling g ↦ c²g changes the boundary metric from γ to c²γ, so the required boundary condition g|_{∂Ω} = γ forces c = 1. When the constant K = sup_{Σ×[0,1]} |R_{γ_t}| > n(n-1), the glued metric satisfies only R_g ≥ -K - 1 < -n(n-1), and no constant rescaling can raise the scalar curvature lower bound to -n(n-1) while preserving the boundary metric exactly. Since Theorem 1.8 relies on Theorem 1.7, this is a load-bearing gap. The statement of Theorem 1.7 may still be true, but the proof as written does not establish it.
- [Proof of Theorem 1.6, final displayed inequality] The displayed inequality 'hat σ λ^{-1} ≤ (1 - ε/4)/(1 - ε/2) σ' has the ratio inverted. Combining the lower bound on \tilde H - (n-1) with the systolic upper bound yields hat σ λ^{-1} ≤ (1 - ε/2)/(1 - ε/4) σ, not the displayed inequality. With the corrected ratio, choosing λ large gives hat σ/λ ≤ (1 - ε/2)/(1 - ε/4) σ < σ, which contradicts the convergence of hat σ/λ to σ as λ → ∞. As written, the displayed inequality does not yield a contradiction, so the proof is incomplete at this point; however, the error appears to be a localized algebra mistake that is repairable from the preceding inequalities.
minor comments (4)
- [Proof of Theorem 1.8] The notation 'C = C(n,γ,γ′)' should be 'C = C(Σ,γ,\hat γ,n)' or similar; also the proof refers to 'γ′' which is not defined at that point.
- [Lemma 3.1, proof] In the display of the comparison ODEs, there is an extra comma after 'w_-(0) = min Σ v0, ,' and the expression for w_+ should be 'w_+(0) = max_Σ v0'. These typos should be corrected for clarity.
- [Proof of Theorem 1.6] Please clarify the precise form of the Brendle–Hung systolic inequality used. The proof applies it as a pointwise bound on \tilde H - (n-1). If the original statement is an integral inequality, the pointwise consequence should be justified using the near-constancy of the mean curvature on \hat Σ_λ established in Proposition 2.8.
- [Throughout] There are numerous typographical issues, e.g., 'g|∂Ω =gRn|∂Ω' in Theorem 1.1, 'the g outward unit normal vector' in Theorem 1.6, and 'Letfε to be the unique solution' in the proof of Theorem 1.6. A careful proofreading pass is recommended.
Circularity Check
No circularity found: the main constant is derived from an external systolic inequality, and no fitted parameter or self-referential definition is used.
full rationale
The derivation chain for Theorem 1.6 is self-contained from the prescribed scalar curvature equation, the a priori estimates, the gluing lemma, and the external Brendle–Hung systolic inequality [5]. The constant (1/2)(4π/(nσ))^n is not fitted: it is the sharp constant appearing in that systolic inequality, and sharpness is independently checked against Horowitz–Myers metrics. The proofs of Theorems 1.7 and 1.8 are interpolation and reduction arguments based on the Shi–Wang–Wei collar construction and the same gluing lemma; they do not assume the total-mean-curvature bound being proved. The only flagged passage is the last sentence of the proof of Theorem 1.7 (Section 3): 'Finally, we can rescale g so that the scalar curvature is bounded from below by −n(n−1).' This is a genuine scaling/correctness gap, because a global rescaling changes the boundary metric from γ to c²γ, but it is not circularity: it does not make the theorem's conclusion an input of its own proof. No self-citation by the author is load-bearing: [5] is a preprint by Brendle and Hung, not by the author, and [21] is an external result. There is no renaming of a known result, no fitted input called a prediction, and no uniqueness theorem imported from the authors. Accordingly, the circularity score is 0.
Assumptions & free parameters
assumptions (3)
- domain assumption Brendle-Hung systolic inequality for compact fill-ins of S^1 x T^(n-2) with scalar curvature >= -n(n-1) and boundary mean curvature >= n-1 (cited as [5]).
- domain assumption Shi-Wang-Wei prescribed-scalar-curvature interpolation construction for boundary metrics gamma_hat and gamma (Lemma 3.1, summarized from [21]).
- standard math Standard parabolic regularity, Krylov-Safonov and Schauder estimates, and maximum principle arguments used in Lemmas 2.3 through 2.6.
Cite this review
Pith. "Pith review of Fill-Ins of Tori with Scalar Curvature Bounded from Below." pith.science (2026). https://pith.science/paper/7VO52P7P
@misc{pith2026241114667,
author = {Pith},
title = {Pith review of: Fill-Ins of Tori with Scalar Curvature Bounded from Below},
year = {2026},
howpublished = {\url{https://pith.science/paper/7VO52P7P}},
note = {Machine review of arXiv:2411.14667}
}
abstract
Let $\gamma$ be a Riemannian metric on $\Sigma = S^1 \times T^{n-2}$, where $3 \leq n \leq 7$. Consider $\Omega = B^2 \times T^{n-2}$ with boundary $\partial \Omega = \Sigma$, and let $g$ be a Riemannian metric on $\Omega$ such that the scalar curvature $R_g \geq -n(n - 1)$ and $g|_{\partial \Omega} = \gamma$. Assuming the mean curvature of $\partial \Omega$ with respect to the outward normal is positive, we establish that the total mean curvature of $\partial \Omega$ is bounded from above by a constant depending only on $n$ and $\gamma$. Furthermore, we compute the sharp constant for this estimate when $\gamma$ is a flat metric. This result resolves a special case of a conjecture by Gromov concerning total mean curvature of fill-in with scalar curvature bounded from below. The proof combines techniques developed by Shi-Tam, Shi-Wang-Wei, as well as recent work by Brendle-Hung on the systolic inequality.
Reference graph
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