Heun polynomial representations for supersingular polynomials at levels 5 and 7

From papers

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=p14+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 p7p\geq7,

ssp(5)(X)=Xm5(X244X16)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 p11p\geq11,

ssp(7)(X)=Xm7(X+1)μ7(X27)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.

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Sources & referencesView supporting material

Primary source

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

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