Conjecture on algebraicity of nonmaximal-order Shintani--Faddeev RM values

From papers

Let βR\beta\in\mathbb R satisfy aβ2+bβ+c=0a\beta^2+b\beta+c=0 with a,b,cZa,b,c\in\mathbb Z and b24acb^2-4ac nonsquare, and let ˚Q2\r\in\mathbb Q^2. Let \shin^{\r}[\beta] and \samech^{\r}[\beta] denote the associated Shintani--Faddeev RM values. Let O\mathcal O be the order relevant to (,˚β)(\r,\beta), let \mm\mm be an O\mathcal O-invertible ideal, and suppose (,˚β)MO,\mm(\r,\beta)\in\mathcal M_{\mathcal O,\mm}. Algebraicity conjecture. Then \shin^{\r}[\beta] is an algebraic unit in an abelian extension of Q(β)\mathbb Q(\beta), and

\samech^{\r}[\beta]\in H_{\mm\infty_2}.

The claim removes the fundamental-discriminant hypothesis from the preceding theorem and extends its algebraicity and class-field containment to suitable nonmaximal orders; numerical evidence is cited, but the conjecture is not resolved.

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Sources & referencesView supporting material

Primary source

Gene S. Kopp, “The Shintani–Faddeev modular cocycle: Stark units from q-Pochhammer ratios”, arXiv:2411.06763 (2025).

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