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Reverse Brunn-Minkowski constant (C70C_{70})

Reverse Brunn-Minkowski constant: determine C70C_{70} or improve its bounds; the repository records 1 (lower) and <∞<\infty (upper).

Editorial MSC2020 classification. Original article codes and source evidence are recorded in the literature directory.

Licensed source statementAs of Repository table at commit 2c1968c (2026-09-26); open while the recorded lower and upper bounds differSource & evidence ↓

Problem statement

For subsets K,L⊂RnK,L\subset\mathbb{R}^n, their Minkowski sum is

K+L := {x+y: x∈K, y∈L}.K+L\ :=\ \{x+y:\ x\in K,\ y\in L\}.

In general, one cannot expect a reverse Brunn-Minkowski inequality for arbitrary compact sets, even with a fixed multiplicative constant. [Bas1995-no-general-reverse]

Milman's reverse Brunn-Minkowski theorem says that for centrally symmetric convex bodies, after putting the bodies in a suitable relative position, one does get a dimension-free reverse inequality. [Bas1995-milman-statement]

More precisely, define CRBMC_{\mathrm{RBM}} as the infimum of constants C>0C>0 such that for every n≥1n\ge 1 and every pair of centrally symmetric convex bodies B1,B2⊂RnB_1,B_2\subset\mathbb{R}^n, there exists a linear map uu with ∣det⁡u∣=1\lvert\det u\rvert=1 satisfying

∣u(B1)+B2∣1/n ≤ C(∣B1∣1/n+∣B2∣1/n).\lvert u(B_1)+B_2\rvert^{1/n}\ \le\ C\bigl(\lvert B_1\rvert^{1/n}+\lvert B_2\rvert^{1/n}\bigr).

[Bas1995-milman-statement]

We define

C70 := CRBM,C_{70}\ :=\ C_{\mathrm{RBM}},

the reverse Brunn-Minkowski constant.

Milman's theorem implies CRBM<∞C_{\mathrm{RBM}}<\infty. [Bas1995-milman-statement]

A trivial lower bound is CRBM≥1C_{\mathrm{RBM}}\ge 1.

Thus the best established range currently is

1 ≤ C70 < ∞.1\ \le\ C_{70}\ <\ \infty.

Lean 4

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Background

References (from the repository page)

  • [Bas1995] Bastero, J.; Bernues, J.; Pena, A. An extension of Milman's reverse Brunn-Minkowski inequality. Geometric and Functional Analysis 5 (1995), no. 3, 572-581. DOI: https://doi.org/10.1007/BF01895832. Publisher page: https://link.springer.com/article/10.1007/BF01895832. arXiv PDF: https://arxiv.org/pdf/math/9501210.pdf. Google Scholar

  • [Bas1995-no-general-reverse] loc: arXiv PDF p.1, Introduction quote: "It is easy to see that one cannot expect the reverse inequality to hold at all, even if it is perturbed by a fixed constant and we restrict ourselves to balls..."

  • [Bas1995-milman-statement] loc: arXiv PDF p.1, Introduction (quoted Milman theorem statement) quote: "There exists a constant C>0C > 0 such that for all n∈Nn \in \mathbb{N} and any balls B1,B2⊂RnB_1, B_2 \subset \mathbb{R}^n we can find a linear transformation u:Rn→Rnu: \mathbb{R}^n \to \mathbb{R}^n with ∣det⁡(u)∣=1|\det(u)| = 1 and ∣u(B1)+B2∣1/n≤C(∣B1∣1/n+∣B2∣1/n)|u(B_1) + B_2|^{1/n} \le C(|B_1|^{1/n} + |B_2|^{1/n})."

  • [Bas1995-proof-history] loc: arXiv PDF p.1, Introduction quote: "Pisier in [Pi 2] gave a new proof by using interpolation and entropy estimates. Milman in [Mil 2] gave another proof by using the 'convex surgery' and achieving also some entropy estimates."

  • [Bas1995-extension-theorem1] loc: arXiv PDF p.1, Theorem 1 quote: "Let 0<p≤10 < p \le 1. There exists C=C(p)≥1C = C(p) \ge 1 such that for all n∈Nn \in \mathbb{N} and all A1,A2⊂RnA_1, A_2 \subset \mathbb{R}^n bodies such that p(A1),p(A2)≥pp(A_1), p(A_2) \ge p, there exists an affine transformation TT ... such that ∣T(A1)+A2∣1/n≤C(∣A1∣1/n+∣A2∣1/n)|T(A_1) + A_2|^{1/n} \le C(|A_1|^{1/n} + |A_2|^{1/n})."

  • [Mil1986] Milman, V. D. Inegalite de Brunn-Minkowsky inverse et applications a la theorie locale des espaces normes. C. R. Acad. Sci. Paris, Serie I 302 (1986), 25-28. MR: 0827101. Google Scholar

  • [Mil1988] Milman, V. D. Isomorphic symmetrization and geometric inequalities. In Geometric Aspects of Functional Analysis (1986/87), Lecture Notes in Mathematics 1317 (1988), 107-131. DOI: https://doi.org/10.1007/BFb0081738. Google Scholar

  • [Pis1989] Pisier, Gilles. The Volume of Convex Bodies and Banach Space Geometry. Cambridge Tracts in Mathematics, vol. 94, Cambridge University Press (1989). DOI: https://doi.org/10.1017/CBO9780511662454. Google Scholar

  • [Pis1989b] Pisier, Gilles. A new approach to several results of V. Milman. Journal fur die reine und angewandte Mathematik 393 (1989), 115-131. DOI: https://doi.org/10.1515/crll.1989.393.115. Google Scholar

Progress & source assessment

Repository table (commit 2c1968c, 26 September 2026): best known lower bound 1; best known upper bound <∞<\infty. Values marked with an asterisk have minimal verification.

Known upper bounds

Bound Reference Comments
<∞<\infty [Mil1986], [Bas1995] Existence of a dimension-free constant in Milman's theorem. [Bas1995-milman-statement]

Known lower bounds

Bound Reference Comments
11 Trivial scaling lower bound.
References
  1. [1]Davis, Damek; Ivanisvili, Paata; Tao, Terence (maintainers). Optimization Constants in Mathematics, github.com/teorth/optimizationproblems (commit 2c1968c, 26 September 2026). — Reverse Brunn-Minkowski constant ($C_{70}$) linkApache-2.0 (repository license); constant pages reproduced with attribution; repository references retained.

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