Modularity conjecture for uniacute spherical codes

Let α,β(0,1)\alpha,\beta \in (0,1) and let L[1,β]{α}L \subseteq [-1,-\beta]\cup\{\alpha\} with αL\alpha \in L. An LL-code is a finite set of unit vectors in Euclidean space whose pairwise inner products lie in LL; write NL(d)N_L(d) for the maximum size of an LL-code in Rd\mathbb{R}^d. A modular LL-code is one for which, after possibly reordering its vectors, its Gram matrix MCM_C dominates a template in the positive-semidefinite order, and write NLmod(d)N_L^{\mathrm{mod}}(d) for the maximum size of a modular LL-code in Rd\mathbb{R}^d. Modularity conjecture. For fixed α\alpha, β\beta, and LL as above,

NL(d)=NLmod(d)+o(d)as d.N_L(d)=N_L^{\mathrm{mod}}(d)+o(d)\quad\text{as }d\to\infty.

The conjecture asserts that modular codes capture the asymptotically maximal size of uniacute spherical codes, up to a sublinear error. The paper notes that all known tight uniacute spherical codes in high dimensions arise from modular codes, but no resolution is given here.

Sources & referencesView supporting material

Primary source

Saba Lepsveridze, Aleksandre Saatashvili and Yufei Zhao, “Uniacute Spherical Codes”, arXiv:2311.17734 (2023).

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