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Fundamental Real Multiplication Values Conjecture

Prove that for any real quadratic irrational \(\rho\) with fundamental discriminant \(\Delta=b^2-4ac\), any \(\mathbf{r} \in \mathbb{Q}^2 \setminus \mathbb{Z}^2\), and any \(A \in \Gamma_\mathbf{r}\) fixing \(\rho\), the special value \(\shin^\mathbf{r}_{A}(\rho)\) is an algebraic unit in an abelian Galois extension of \(\mathbb{Q}(\sqrt{\Delta})\), and that for any Galois automorphism \(g\) with \(g(\sqrt{\Delta}) = -\sqrt{\Delta}\), one has \(|g(\shin^\mathbf{r}_{A}(\rho))| = 1\).

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Background

This strengthening of the Minimalist RMVC asserts that Shintani–Faddeev cocycle values at fundamental discriminants are algebraic units in abelian extensions of the base real quadratic field and have unit absolute value under the nontrivial Galois action. It is implied by the Stark–Tate Conjecture.

References

Conjecture [Fundamental Real Multiplication Values Conjecture] Let \rho \in \R such that a\rho2 + b\rho + c = 0 with a,b,c \in \Z and \Delta = b2-4ac is a fundamental discriminant. Let \r \in \Q2 \setminus \Z2 and A \in \Gamma_\r such that A \cdot \rho = \rho. Then: (1) \shin\r_{!A}(\rho) is an algebraic unit in an abelian Galois extension of \Q(\sqrt{\Delta}). (2) If g \in \Gal(\ol{\Q}/\Q) such that g(\sqrt{\Delta}) = -\sqrt{\Delta}, then \abs{g(\shin\r_{!A}(\rho))}=1.

A Constructive Approach to Zauner's Conjecture via the Stark Conjectures (2501.03970 - Appleby et al., 7 Jan 2025) in Conjecture 2.19, Section 2.6 (The main conjectures)