Heun polynomial representations for supersingular polynomials at levels 5 and 7

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Let pp be prime. For N=5N=5, define m5m_{5}, μ5\mu_{5}, ϕ\phi, and Hl5(X)Hl_{5}(X) as in the displayed formulas below; for N=7N=7, define m7m_{7}, μ7\mu_{7}, and Hl7(X)Hl_{7}(X) similarly.

m5=p−14+14(1−(−1p))−μ5,μ5=12(1−(−5p)),ϕ=1+52,m_{5}=\frac{p-1}{4}+\frac14\left(1-\left(\frac{-1}{p}\right)\right)-\mu_{5},\quad \mu_{5}=\frac12\left(1-\left(\frac{-5}{p}\right)\right),\quad \phi=\frac{1+\sqrt5}{2}, Hl5(X)=Hl(−ϕ10,−(22μ5+3)ϕ54;−m5,μ5+12+14(−1p),1,μ5+12;4ϕ5X),Hl_{5}(X)=Hl\left(-\phi^{10},-\frac{(22\mu_{5}+3)\phi^{5}}4;-m_{5},\mu_{5}+\frac12+\frac14\left(\frac{-1}{p}\right),1,\mu_{5}+\frac12;\frac{4\phi^{5}}X\right),

and define m7m_{7}, μ7\mu_{7}, and Hl7(X)Hl_{7}(X) by the corresponding formulas in the claim.

Heun polynomial representation conjecture. For every prime p≥7p\geq7,

ssp(5∗)(X)=Xm5(X2−44X−16)μ5Hl5(X)(modp).ss_{p}^{(5*)}(X)=X^{m_{5}}(X^{2}-44X-16)^{\mu_{5}}Hl_{5}(X)\pmod p.

For p=5p=5 and p≥11p\geq11,

ssp(7∗)(X)=Xm7(X+1)μ7(X−27)μ7Hl7(X)(modp).ss_{p}^{(7*)}(X)=X^{m_{7}}(X+1)^{\mu_{7}}(X-27)^{\mu_{7}}Hl_{7}(X)\pmod p.

These formulas conjecturally extend the hypergeometric descriptions of supersingular polynomials to levels 5 and 7, where Heun polynomials replace hypergeometric polynomials. The source supplies no resolution evidence.

References

Primary source

Tomoaki Nakaya, “The number of linear factors of supersingular polynomials and sporadic simple groups”, arXiv:1809.02363 (2018).

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