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25 April 2024
 
  » arxiv » 0907.0776

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Delaunay polytopes derived from the Leech lattice
Mathieu Dutour Sikiric ; Konstantin Rybnikov ;
Date 4 Jul 2009
AbstractGiven a lattice L of R^n, a polytope D is called a Delaunay polytope in L if the set of its vertices is Scap L where S is a sphere having no lattice points in its interior. D is called perfect if the only ellipsoid in R^n that contains Scap L is exactly S.
For a vector v of the Leech lattice Lambda_{24} we define Lambda_{24}(v) to be the lattice of vectors of Lambda_{24} orthogonal to v. We studied Delaunay polytopes of L=Lambda_{24}(v) for |v|^2<=22. We found some remarkable examples of Delaunay polytopes in such lattices and disproved a number of long standing conjectures. In particular, we discovered:
--Perfect Delaunay polytopes of lattice width 4; previously, the largest known width was 2.
--Perfect Delaunay polytopes in L, which can be extended to perfect Delaunay polytopes in superlattices of L of the same dimension.
--Polytopes that are perfect Delaunay with respect to two lattices $Lsubset L’$ of the same dimension.
--Perfect Delaunay polytopes D for L with |Aut L|=6|Aut D|: all previously known examples had |Aut L|=|Aut D| or |Aut L|=2|Aut D|.
--Antisymmetric perfect Delaunay polytopes in L, which cannot be extended to perfect (n+1)-dimensional centrally symmetric Delaunay polytopes.
--Lattices, which have several orbits of non-isometric perfect Delaunay polytopes.
Finally, we derived an upper bound for the covering radius of Lambda_{24}(v)^{*}, which generalizes the Smith bound and we prove that it is met only by Lambda_{23}^{*}, the best known lattice covering in R^{23}.
Source arXiv, 0907.0776
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