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

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Oura introduced Eisenstein polynomials φH1(x0,x1)\varphi_\ell^{H_1}(x_0,x_1) associated with the group H1H_1, and, when this polynomial is nonzero, let φH1~\widetilde{\varphi_\ell^{H_1}} denote it divided by its x0x_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 {e1θπ/2θ2π/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(φH1~)Th(\widetilde{\varphi_\ell^{H_1}}) lie on the circle {e1θπ/2θ2π/3}\{e^{\sqrt{-1}\theta}\mid \pi/2\leq\theta\leq2\pi/3\}.
  2. The zeros of Th(φH1~)Th(\widetilde{\varphi_\ell^{H_1}}) are the same as those of Th(φ+4H1~)Th(\widetilde{\varphi_{\ell+4}^{H_1}}).
  3. If pp is an odd prime, then the coefficients of Th(φ2(p1)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.

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Sources & referencesView supporting material

Primary source

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

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