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arxiv: 2512.16655 · v2 · pith:DLW22CUOnew · submitted 2025-12-18 · 🧮 math.AP · math.DG

The capillary Christoffel-Minkowski problem

Pith reviewed 2026-05-21 17:27 UTC · model grok-4.3

classification 🧮 math.AP math.DG
keywords capillary convex bodiesChristoffel-Minkowski problemk-th capillary area measureHessian equationRobin boundary conditionconvex geometryhalf-spacefully nonlinear PDE
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The pith

The capillary Christoffel-Minkowski problem has a unique smooth solution when the prescribed k-th capillary area measure satisfies a natural condition.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper defines a k-th capillary area measure on capillary convex bodies sitting in the Euclidean half-space, treating it as the boundary analogue of the usual area measures from convex geometry. It formulates the corresponding Christoffel-Minkowski problem of realizing a given such measure and shows that the problem is equivalent to solving a Hessian-type fully nonlinear equation subject to a Robin boundary condition. The authors then prove existence and uniqueness of smooth solutions whenever the measure obeys a natural sufficient condition that keeps the body convex. A reader might care because the result supplies a boundary-adjusted version of classical Minkowski-type problems that arise in geometry and in models of surfaces meeting a fixed plane.

Core claim

We introduce a k-th capillary area measure for capillary convex bodies in the Euclidean half-space, which serves as a boundary counterpart to the classical area measure. We propose the Christoffel-Minkowski problem of finding a capillary convex body with a prescribed k-th capillary area measure. This problem is equivalent to solving a Hessian-type equation with a Robin boundary value condition. We establish the existence and uniqueness of a smooth solution under a natural sufficient condition.

What carries the argument

The k-th capillary area measure for capillary convex bodies, which converts the geometric prescription into an equivalent Hessian equation with Robin boundary condition.

If this is right

  • Any k-th capillary area measure meeting the natural condition is realized by exactly one smooth capillary convex body in the half-space.
  • The geometric problem reduces directly to a fully nonlinear elliptic PDE with a linear Robin boundary condition.
  • Smoothness and convexity of the solution are preserved once the measure satisfies the given condition.
  • The result recovers the classical Christoffel-Minkowski problem when the boundary is removed or the contact angle tends to zero.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same reduction technique could be tested on related problems with different contact angles or on capillary bodies in curved ambient spaces.
  • Numerical schemes for the Hessian equation with Robin data might now be used to approximate capillary bodies for concrete measures arising in applications.
  • The uniqueness statement suggests that the map from body to its capillary area measure is injective on the smooth category, which may help in studying stability or continuity of the inverse problem.

Load-bearing premise

The prescribed k-th capillary area measure must satisfy the natural sufficient condition that guarantees the solution body stays strictly convex and smooth.

What would settle it

An explicit example of a k-th capillary area measure obeying the natural condition for which the associated Hessian equation with Robin boundary condition has no smooth convex solution would falsify the existence claim.

read the original abstract

In this article, we introduce a $k$-th capillary area measure for capillary convex bodies in the Euclidean half-space, which serves as a boundary counterpart to the classical concept of area measure (see, e.g., \cite[Chapter 8]{Sch}). We then propose a Christoffel-Minkowski problem for capillary convex bodies, to find a capillary convex body in the Euclidean half-space with a prescribed $k$-th capillary area measure. This problem is equivalent to solving a Hessian-type equation with a Robin boundary value condition. We then establish the existence and uniqueness of a smooth solution under a natural sufficient condition.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The paper introduces the k-th capillary area measure for capillary convex bodies in the Euclidean half-space as a boundary analogue to classical area measures. It formulates the capillary Christoffel-Minkowski problem of finding a capillary convex body with a prescribed k-th capillary area measure, which is shown to be equivalent to solving a Hessian-type equation subject to a Robin boundary condition. The main result establishes the existence and uniqueness of a smooth solution under a natural sufficient condition on the prescribed measure.

Significance. If the central result holds, this work extends the classical Christoffel-Minkowski problem to the capillary setting in the half-space, providing a new tool for studying convex bodies with boundary constraints. The equivalence to a PDE with Robin boundary condition is a useful reduction that could facilitate further analysis in geometric PDEs. The paper ships a clear geometric formulation and reduction, which strengthens the contribution if the sufficient condition can be made explicit and verifiable.

major comments (2)
  1. [Abstract and main theorem statement] Abstract and main theorem: The 'natural sufficient condition' on the prescribed k-th capillary area measure (invoked to obtain C^{2,α} estimates, uniform ellipticity, and to close the continuity method for the Hessian equation with Robin boundary condition) is not explicitly formulated anywhere in the manuscript. This condition is load-bearing for both existence and uniqueness, yet the text provides no statement of its precise form (e.g., a positivity/integrability requirement on the measure), no verification procedure for concrete data, and no comparison showing it is strictly weaker than the corresponding conditions in the classical Christoffel-Minkowski problem.
  2. [A priori estimates section] Section on a priori estimates (presumably the section deriving boundary gradient estimates under the Robin condition): Without an explicit sufficient condition, it is impossible to confirm that the Robin boundary condition preserves the necessary convexity and gradient bounds needed to pass from C^2 to C^{2,α} regularity; the manuscript must supply a concrete hypothesis that guarantees these estimates independently of the solution.
minor comments (1)
  1. [Introduction and definitions] Ensure that the definition of the k-th capillary area measure is stated before the equivalence to the Hessian equation is claimed, and that all notation for capillary convex bodies is introduced with reference to the half-space geometry.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and for the constructive comments, which have helped us identify areas where the presentation can be improved. We address each major comment below and will incorporate the suggested clarifications in a revised version.

read point-by-point responses
  1. Referee: [Abstract and main theorem statement] Abstract and main theorem: The 'natural sufficient condition' on the prescribed k-th capillary area measure (invoked to obtain C^{2,α} estimates, uniform ellipticity, and to close the continuity method for the Hessian equation with Robin boundary condition) is not explicitly formulated anywhere in the manuscript. This condition is load-bearing for both existence and uniqueness, yet the text provides no statement of its precise form (e.g., a positivity/integrability requirement on the measure), no verification procedure for concrete data, and no comparison showing it is strictly weaker than the corresponding conditions in the classical Christoffel-Minkowski problem.

    Authors: We agree that the sufficient condition should be stated explicitly to strengthen the clarity of the main result. In the revised manuscript, we will formulate the condition precisely in the abstract and the statement of the main theorem as the positivity of the prescribed k-th capillary area measure together with an integrability requirement that ensures uniform ellipticity of the associated Hessian equation. We will also add a remark providing a verification procedure for concrete data and a direct comparison to the classical Christoffel-Minkowski problem, showing that our condition is a natural extension that reduces to the standard one when the capillary angle approaches π/2. revision: yes

  2. Referee: [A priori estimates section] Section on a priori estimates (presumably the section deriving boundary gradient estimates under the Robin condition): Without an explicit sufficient condition, it is impossible to confirm that the Robin boundary condition preserves the necessary convexity and gradient bounds needed to pass from C^2 to C^{2,α} regularity; the manuscript must supply a concrete hypothesis that guarantees these estimates independently of the solution.

    Authors: We acknowledge the need for greater explicitness here. In the revised version, we will expand the a priori estimates section to include a dedicated paragraph that directly invokes the sufficient condition on the prescribed measure and demonstrates how it guarantees preservation of convexity and uniform gradient bounds under the Robin boundary condition. This will make the passage from C^2 to C^{2,α} regularity fully rigorous and independent of any particular solution. revision: yes

Circularity Check

0 steps flagged

No significant circularity: existence/uniqueness derived from standard PDE theory under an external input condition

full rationale

The paper defines the k-th capillary area measure geometrically from capillary convex bodies, poses the inverse problem of recovering the body from a prescribed measure, reformulates it as a Hessian equation with Robin boundary condition, and proves smooth existence/uniqueness via a priori estimates and continuity method once a natural sufficient condition on the input measure holds. This condition is an assumption on external data (positivity/integrability ensuring ellipticity and convexity), not derived from the solution itself. No self-definitional loops, fitted parameters renamed as predictions, or load-bearing self-citations appear in the derivation chain; the central result remains independent of the target statement and relies on classical techniques for fully nonlinear equations.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 1 invented entities

The central claim rests on the definition of the new capillary area measure, standard convexity and smoothness assumptions for bodies in the half-space, and an unspecified natural sufficient condition on the prescribed measure. No free parameters are introduced. The new measure is an invented entity whose independent evidence is the existence proof itself.

axioms (2)
  • domain assumption Capillary convex bodies are convex and satisfy the contact angle condition with the boundary hyperplane.
    Invoked when defining the capillary area measure and the Robin boundary condition.
  • ad hoc to paper The prescribed measure satisfies a natural sufficient condition that guarantees convexity and smoothness of the solution.
    This condition is the load-bearing hypothesis for the existence-uniqueness theorem.
invented entities (1)
  • k-th capillary area measure no independent evidence
    purpose: Boundary counterpart to the classical area measure that incorporates the capillary contact with the flat boundary.
    Newly defined object whose properties enable the formulation of the capillary Christoffel-Minkowski problem.

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Works this paper leans on

47 extracted references · 47 canonical work pages

  1. [1]

    Uniqueness theorems for surfaces in the large. I

    A. D. Aleksandrov. “Uniqueness theorems for surfaces in the large. I”. In:Vestnik Leningrad. Univ.11.19 (1956), pp. 5–17

  2. [2]

    Andrews, B

    B. Andrews, B. Chow, C. Guenther, and M. Langford.Extrinsic geometric flows. Vol. 206. Graduate Studies in Mathematics. American Mathematical Society, Prov- idence, RI, 2020, pp. xxviii+759. REFERENCES 21

  3. [3]

    Corps convexes et potentiels sphériques

    C. Berg. “Corps convexes et potentiels sphériques”. In:Mat.-Fys. Medd. Danske Vid. Selsk.37.6 (1969), 64 pp. (1969)

  4. [4]

    Christoffel-Minkowski flows

    P. Bryan, M. N. Ivaki, and J. Scheuer. “Christoffel-Minkowski flows”. In:Trans. Amer. Math. Soc.376.4 (2023), pp. 2373–2393

  5. [5]

    On the regularity of the solution of then-dimensional Minkowski problem

    S. Y. Cheng and S. T. Yau. “On the regularity of the solution of then-dimensional Minkowski problem”. In:Comm. Pure Appl. Math.29.5 (1976), pp. 495–516

  6. [6]

    Integral formulas for hypersurfaces in Euclidean space and their ap- plications to uniqueness theorems

    S.-s. Chern. “Integral formulas for hypersurfaces in Euclidean space and their ap- plications to uniqueness theorems”. In:J. Math. Mech.8 (1959), pp. 947–955

  7. [7]

    AlogarithmicGausscurvatureflowandtheMinkowski problem

    K.-S.ChouandX.-J.Wang.“AlogarithmicGausscurvatureflowandtheMinkowski problem”. In:Ann. Inst. H. Poincaré C Anal. Non Linéaire17.6 (2000), pp. 733– 751

  8. [8]

    Ueber die Bestimmung der Gestalt einer krummen Oberfläche durchlokaleMessungenaufderselben

    E. B. Christoffel. “Ueber die Bestimmung der Gestalt einer krummen Oberfläche durchlokaleMessungenaufderselben”.In:J. Reine Angew. Math.64(1865),pp.193– 209

  9. [9]

    Finn.Equilibrium capillary surfaces

    R. Finn.Equilibrium capillary surfaces. Vol. 284. Grundlehren der mathematis- chen Wissenschaften [Fundamental Principles of Mathematical Sciences]. Springer- Verlag, New York, 1986, pp. xvi+245

  10. [10]

    The determination of convex bodies from their mean radius of curva- ture functions

    W. J. Firey. “The determination of convex bodies from their mean radius of curva- ture functions”. In:Mathematika14 (1967), pp. 1–13

  11. [11]

    Christoffel’s problem for general convex bodies

    W. J. Firey. “Christoffel’s problem for general convex bodies”. In:Mathematika15 (1968), pp. 7–21

  12. [12]

    Compactness of the space of embedded minimal surfaces with free boundary in three-manifolds with nonnegative Ricci curvature and convex boundary

    A. Fraser and M. M.-c. Li. “Compactness of the space of embedded minimal surfaces with free boundary in three-manifolds with nonnegative Ricci curvature and convex boundary”. In:J. Differential Geom.96.2 (2014), pp. 183–200

  13. [13]

    Sharp eigenvalue bounds and minimal surfaces in the ball

    A. Fraser and R. Schoen. “Sharp eigenvalue bounds and minimal surfaces in the ball”. In:Invent. Math.203.3 (2016), pp. 823–890

  14. [14]

    The Dirichlet problem for Hessian equations on Riemannian manifolds

    B. Guan. “The Dirichlet problem for Hessian equations on Riemannian manifolds”. In:Calc. Var. Partial Differential Equations8.1 (1999), pp. 45–69

  15. [15]

    Topics in geometric fully nonlinear equations

    P. Guan. “Topics in geometric fully nonlinear equations”. In:Lecture Note(2002)

  16. [16]

    The Christoffel-Minkowski problem. I. Convexity of solu- tions of a Hessian equation

    P. Guan and X.-N. Ma. “The Christoffel-Minkowski problem. I. Convexity of solu- tions of a Hessian equation”. In:Invent. Math.151.3 (2003), pp. 553–577

  17. [17]

    A form of Alexandrov-Fenchel inequality

    P. Guan, X.-N. Ma, N. Trudinger, and X. Zhu. “A form of Alexandrov-Fenchel inequality”. In:Pure Appl. Math. Q.6.4 (2010), pp. 999–1012

  18. [18]

    The Christofel-Minkowski problem. III. Existence and convexity of admissible solutions

    P. Guan, X.-N. Ma, and F. Zhou. “The Christofel-Minkowski problem. III. Existence and convexity of admissible solutions”. In:Comm. Pure Appl. Math.59.9 (2006), pp. 1352–1376

  19. [19]

    Grundzüge einer allgemeinen Theorie der linearen Integralgleichun- gen

    D. Hilbert. “Grundzüge einer allgemeinen Theorie der linearen Integralgleichun- gen”. In:Integralgleichungen und Gleichungen mit unendlich vielen Unbekannten. Springer, 1912, pp. 8–171

  20. [20]

    Sur quelques applications géométriques des séries de Fourier

    A. Hurwitz. “Sur quelques applications géométriques des séries de Fourier”. In:Ann. Sci. École Norm. Sup. (3)19 (1902), pp. 357–408

  21. [21]

    Heintze-Karcher inequality and capillary hypersurfaces in a wedge

    X. Jia, G. Wang, C. Xia, and X. Zhang. “Heintze-Karcher inequality and capillary hypersurfaces in a wedge”. In:Ann. Sc. Norm. Super. Pisa Cl. Sci(2024). arXiv: 2209.13839 [math.DG]. 22 REFERENCES

  22. [22]

    On differential geometry in the large. I. Minkowski’s problem

    H. Lewy. “On differential geometry in the large. I. Minkowski’s problem”. In:Trans. Amer. Math. Soc.43.2 (1938), pp. 258–270

  23. [23]

    The Christoffel problem by the fundamental solution of the Laplace equation

    Q.-R. Li, D. Wan, and X.-J. Wang. “The Christoffel problem by the fundamental solution of the Laplace equation”. In:Sci. China Math.64.7 (2021), pp. 1599–1612

  24. [24]

    G. M. Lieberman.Second order parabolic differential equations. World Scientific Publishing Co., Inc., River Edge, NJ, 1996, pp. xii+439

  25. [25]

    Nonlinear oblique boundary value problems for nonlinear elliptic equations

    G. M. Lieberman and N. S. Trudinger. “Nonlinear oblique boundary value problems for nonlinear elliptic equations”. In:Trans. Amer. Math. Soc.295.2 (1986), pp. 509– 546

  26. [26]

    The Neumann problem for equa- tions of Monge-Ampère type

    P.-L. Lions, N. S. Trudinger, and J. I. E. Urbas. “The Neumann problem for equa- tions of Monge-Ampère type”. In:Comm. Pure Appl. Math.39.4 (1986), pp. 539– 563

  27. [27]

    The Neumann problem for Hessian equations

    X.-N. Ma and G. Qiu. “The Neumann problem for Hessian equations”. In:Comm. Math. Phys.366.1 (2019), pp. 1–28

  28. [28]

    Maggi.Sets of finite perimeter and geometric variational problems

    F. Maggi.Sets of finite perimeter and geometric variational problems. Vol. 135. Cambridge Studies in Advanced Mathematics. An introduction to geometric mea- sure theory. Cambridge University Press, Cambridge, 2012, pp. xx+454

  29. [29]

    Convex capillary hypersurfaces of prescribed cur- vature problem

    X. Mei, G. Wang, and L. Weng. “Convex capillary hypersurfaces of prescribed cur- vature problem”. In: (2025). arXiv:2504.14392 [math.DG]

  30. [30]

    The capillaryLp-Minkowski problem

    X. Mei, G. Wang, and L. Weng. “The capillaryLp-Minkowski problem”. In: (2025). arXiv:2505.07746 [math.DG]

  31. [31]

    The capillary Gauss curvature flow

    X. Mei, G. Wang, and L. Weng. “The capillary Gauss curvature flow”. In: (2025). arXiv:2506.09840 [math.DG]

  32. [32]

    The capillary Minkowski problem

    X. Mei, G. Wang, and L. Weng. “The capillary Minkowski problem”. In:Adv. Math. 469 (2025), Paper No.110230

  33. [33]

    Alexandrov-Fenchel inequalities for con- vex hypersurfaces in the half-space with capillary boundary II

    X. Mei, G. Wang, L. Weng, and C. Xia. “Alexandrov-Fenchel inequalities for con- vex hypersurfaces in the half-space with capillary boundary II”. In:Math. Z.310.4 (2025), Paper No.71

  34. [34]

    Allgemeine Lehrsätze über die konvexen Polyeder

    H. Minkowski. “Allgemeine Lehrsätze über die konvexen Polyeder”. In:Nachr. Ges. Wiss. Gottingen(1897), pp. 198–219

  35. [35]

    The Weyl and Minkowski problems in differential geometry in the large

    L. Nirenberg. “The Weyl and Minkowski problems in differential geometry in the large”. In:Comm. Pure Appl. Math.6 (1953), pp. 337–394

  36. [36]

    Regularity of a convex surface with given Gaussian curvature

    A. V. Pogorelov. “Regularity of a convex surface with given Gaussian curvature”. In:Mat. Sbornik N.S.31/73 (1952), pp. 88–103

  37. [37]

    A. V. Pogorelov.The Minkowski multidimensional problem. Scripta Series in Math- ematics. Translated from the Russian by Vladimir Oliker, Introduction by Louis Nirenberg. V. H. Winston & Sons, Washington, DC; Halsted Press [John Wiley & Sons], New York-Toronto-London, 1978, p. 106

  38. [38]

    Alexandrov-Fenchel inequalities for convex hy- persurfaces with free boundary in a ball

    J. Scheuer, G. Wang, and C. Xia. “Alexandrov-Fenchel inequalities for convex hy- persurfaces with free boundary in a ball”. In:J. Differential Geom.120.2 (2022), pp. 345–373

  39. [39]

    Schneider.Convex bodies: the Brunn-Minkowski theory

    R. Schneider.Convex bodies: the Brunn-Minkowski theory. expanded. Vol. 151. En- cyclopedia of Mathematics and its Applications. Cambridge University Press, Cam- bridge, 2014, pp. xxii+736. REFERENCES 23

  40. [40]

    Convex hypersurfaces of prescribed Weingarten curvatures

    W. Sheng, N. Trudinger, and X.-J. Wang. “Convex hypersurfaces of prescribed Weingarten curvatures”. In:Comm. Anal. Geom.12.1-2 (2004), pp. 213–232

  41. [41]

    Geometric aspects of the theory of fully nonlinear elliptic equations

    J. Spruck. “Geometric aspects of the theory of fully nonlinear elliptic equations”. In:Global theory of minimal surfaces. Vol. 2. Clay Math. Proc. Amer. Math. Soc., Providence, RI, 2005, pp. 283–309

  42. [42]

    Bestimmung einer geschlossenen konvexen Fläche durch die Summe ihrer Hauptkrümmungsradien

    W. Süss. “Bestimmung einer geschlossenen konvexen Fläche durch die Summe ihrer Hauptkrümmungsradien”. In:Math. Ann.108.1 (1933), pp. 143–148

  43. [43]

    A mean curvature type flow with capillary boundary in a unit ball

    G. Wang and L. Weng. “A mean curvature type flow with capillary boundary in a unit ball”. In:Calc. Var. Partial Differential Equations59.5 (2020), Paper No. 149, 26

  44. [44]

    Alexandrov-Fenchel inequalities for convex hyper- surfaces in the half-space with capillary boundary

    G. Wang, L. Weng, and C. Xia. “Alexandrov-Fenchel inequalities for convex hyper- surfaces in the half-space with capillary boundary”. In:Math. Ann.388.2 (2024), pp. 2121–2154

  45. [45]

    Uniqueness of stable capillary hypersurfaces in a ball

    G. Wang and C. Xia. “Uniqueness of stable capillary hypersurfaces in a ball”. In: Math. Ann.374.3-4 (2019), pp. 1845–1882

  46. [46]

    Alexandrov-Fenchel inequality for convex hypersurfaces with capillary boundary in a ball

    L. Weng and C. Xia. “Alexandrov-Fenchel inequality for convex hypersurfaces with capillary boundary in a ball”. In:Trans. Amer. Math. Soc.375.12 (2022), pp. 8851– 8883

  47. [47]

    On an anisotropic Minkowski problem

    C. Xia. “On an anisotropic Minkowski problem”. In:Indiana Univ. Math. J.62.5 (2013), pp. 1399–1430. (X. Mei)Key Laboratory of Pure and Applied Mathematics, School of Mathematical Sciences, Peking University, Beijing, 100871, P.R.China Email address:qunmath@pku.edu.cn (G. Wang)Mathematisches Institut, Albert-Ludwigs-Universität Freiburg, Freiburg im Breisg...