E8 and Leech limiting-ratio conjecture

Let ff and f^\widehat f be the limiting functions obtained by forcing roots at lattice vector lengths. For 0<n<100<n<10, use the E8E_8 vector lengths; for 0<n<260<n<26, use the Leech lattice vector lengths. Define

p24(n)=n8284n7+35312n62510720n5+111652352n43180064256n3+56651266048n2577142292480n+2574499479552.p_{24}(n)=n^8-284n^7+35312n^6-2510720n^5+111652352n^4-3180064256n^3+56651266048n^2-577142292480n+2574499479552.

E8 and Leech limiting-ratio conjecture. In the E8E_8 case,

f(0)f^(0)=n456n3+1184n211200n+4032016(n10)(n14)(n18).\frac{f(0)}{\widehat f(0)}=-\frac{n^4-56n^3+1184n^2-11200n+40320}{16(n-10)(n-14)(n-18)}.

In the Leech case,

f(0)f^(0)=p24(n)32(n26)(n34)(n38)(n42)(n3116n2+4480n57024).\frac{f(0)}{\widehat f(0)}=-\frac{p_{24}(n)}{32(n-26)(n-34)(n-38)(n-42)(n^3-116n^2+4480n-57024)}.

These formulas predict the limiting linear-programming ratios across continuous ranges of dimensions and extend the exceptional-dimension investigations beyond 88 and 2424; the source supplies numerical motivation but no proof.

Sources & referencesView supporting material

Primary source

Henry Cohn and Stephen D. Miller, “Some properties of optimal functions for sphere packing in dimensions 8 and 24”, arXiv:1603.04759 (2016).

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