Solution of the propeller conjecture in R3

  • Authors:
  • Steven Heilman;Aukosh Jagannath;Assaf Naor

  • Affiliations:
  • Courant Institute, NYU, New York, NY, USA;Courant Institute, NYU, New York, NY, USA;Courant Institute, NYU, New York, NY, USA

  • Venue:
  • STOC '12 Proceedings of the forty-fourth annual ACM symposium on Theory of computing
  • Year:
  • 2012

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Abstract

It is shown that every measurable partition {A1,..., Ak} of R3 satisfies: ∑i=1k|intAi xe-1/2|x|22dx|22≤ 9π2. Let P1,P2,P3 be the partition of R2 into 120o sectors centered at the origin. The bound (1) is sharp, with equality holding if Ai=Pi x R for i∈ {1,2,3} and Ai=∅ for i∈ {4,...,k}. This settles positively the 3-dimensional Propeller Conjecture of Khot and Naor (FOCS 2008). The proof of (1) reduces the problem to a finite set of numerical inequalities which are then verified with full rigor in a computer-assisted fashion. The main consequence (and motivation) of (1) is complexity-theoretic: the Unique Games hardness threshold of the Kernel Clustering problem with 4 x 4 centered and spherical hypothesis matrix equals 2π/3.