Improve the bounds on the kissing number $K(5)$ in dimension 5
Statement
The kissing number $K(d)$ is the maximum number of non-overlapping unit spheres in $\mathbb{R}^d$ that can simultaneously touch a central unit sphere; equivalently, the maximum number of unit vectors in $\mathbb{R}^d$ with pairwise angular separation at least $60^\circ$ (pairwise inner product $\le \tfrac12$). Dimension 5 is the smallest dimension in which $K(d)$ is unknown: currently $40 \le K(5) \le 44$. Either determine $K(5)$ exactly, or improve one of the bounds with a verifiable certificate: raise the lower bound by exhibiting $N \ge 41$ unit vectors in $\mathbb{R}^5$ with all pairwise inner products $\le \tfrac12$, or lower the upper bound below 44 with a certificate.
Acceptance. FULLY RESOLVES: a proof determining $K(5)$ exactly (matching lower and upper bounds). PARTIAL (lower bound): a machine-checkable list of $N \ge 41$ unit vectors in $\mathbb{R}^5$ (coordinates) such that every pairwise inner product is $\le \tfrac12$ within a stated numerical tolerance -- verifier: normalize, form the Gram matrix, check off-diagonal entries $\le \tfrac12$; this would prove $K(5) \ge N$. PARTIAL (upper bound): a dual-feasible SDP/LP certificate proving $K(5) \le 43$ or lower, checkable by evaluating the feasibility of the provided dual solution.
Background
The lower bound $K(5) \ge 40$ is realized by the minimal vectors of the $D_5$ root lattice (the 40 permutations of $(\pm1,\pm1,0,0,0)$; Korkine & Zolotareff, 1873). The upper bound $K(5) \le 44$ comes from semidefinite-programming linear-programming bounds (Bachoc & Vallentin, 'New upper bounds for kissing numbers from semidefinite programming', JAMS 2008; refined by Mittelmann & Vallentin, arXiv:0902.1105, 2010). $K(d)$ is known exactly only for $d=1,2,3,4,8,24$. Sources: Henry Cohn's maintained table of kissing-number bounds (cohn.mit.edu/kissing-numbers); 'Kissing numbers -- a survey' (arXiv:1507.03631, 2015); Conway & Sloane, 'Sphere Packings, Lattices and Groups', ch. 1.
References
| Ref | Source | Type |
|---|---|---|
| REF-01 | Henry Cohn -- Table of kissing-number bounds | link |
| REF-02 | Kissing numbers -- a survey (arXiv:1507.03631, 2015) | link |
| REF-03 | Mittelmann & Vallentin -- High accuracy SDP bounds for kissing numbers (2010) | link |
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