Oura's conjecture on analogies between Eisenstein series and Eisenstein polynomials

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Oura introduced Eisenstein polynomials φℓH1(x0,x1)\varphi_\ell^{H_1}(x_0,x_1) associated with the group H1H_1, and, when this polynomial is nonzero, let φℓH1~\widetilde{\varphi_\ell^{H_1}} denote it divided by its x0ℓx_0^\ell coefficient. Let ThTh denote the transform used to associate a univariate polynomial to this normalized Eisenstein polynomial. For an odd prime pp, a rational number aa is pp-integral when vp(a)≥0v_p(a)\geq 0, where vpv_p is the valuation on Q\mathbb{Q}. The relevant Eisenstein-series properties concern zeros on the arc {e−1θ∣π/2≤θ≤2π/3}\{e^{\sqrt{-1}\theta}\mid \pi/2\leq\theta\leq2\pi/3\}, equality of zeros after increasing the index by the corresponding weight step, and pp-integrality of coefficients.

Oura's conjecture. The analogous properties hold for the transforms of the normalized Eisenstein polynomials, namely:

  1. All zeros of Th(φℓH1~)Th(\widetilde{\varphi_\ell^{H_1}}) lie on the circle {e−1θ∣π/2≤θ≤2π/3}\{e^{\sqrt{-1}\theta}\mid \pi/2\leq\theta\leq2\pi/3\}.
  2. The zeros of Th(φℓH1~)Th(\widetilde{\varphi_\ell^{H_1}}) are the same as those of Th(φℓ+4H1~)Th(\widetilde{\varphi_{\ell+4}^{H_1}}).
  3. If pp is an odd prime, then the coefficients of Th(φ2(p−1)H1~)Th(\widetilde{\varphi_{2(p-1)}^{H_1}}) are pp-integral.

These claims are proposed as analogues of known properties of Eisenstein series, connecting the zero distributions, index-shift behavior, and arithmetic integrality of the two theories. The supplied text does not state that any of the three claims has been proved or disproved.

References

Primary source

Tsuyoshi Miezaki, “On Eisenstein polynomials and zeta polynomials”, arXiv:1807.02744 (2020).

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