Conjectural structure of the Iwasawa module in a real quadratic case

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Let K=Q(D)K=\mathbb{Q}(\sqrt{D}), where D=pqD=pq with p≡5(mod8)p\equiv 5\pmod 8 and q≡1(mod8)q\equiv 1\pmod 8, and suppose

(2q)4≠(−1)q−18.\left(\dfrac{2}{q}\right)_4\neq (-1)^{\frac{q-1}{8}}.

Assume also

(pq)=1,(pq)4=−(qp)4,q≡9(mod16),N(ε2D)=−1.\left(\dfrac{p}{q}\right)=1,\qquad \left(\dfrac{p}{q}\right)_4=-\left(\dfrac{q}{p}\right)_4,\qquad q\equiv 9\pmod {16},\qquad N(\varepsilon_{2D})=-1.

Let X∞X_{\infty} be the Iwasawa module of the cyclotomic Z2\mathbb{Z}_2-extension of KK, and let A1A_1 denote the class-group module used in the paper. The paper's conjecture. Under these assumptions,

X∞≅A1.X_{\infty}\cong A_1.

This is proposed for a case left unresolved in the cited classification. The surrounding discussion says that the module is known to be finite in some comparable cases, but that the point where the class-group chain stops growing is difficult to predict; no resolution of this specific assertion is given.

References

Primary source

Josue Avila, “Iwasawa module of the cyclotomic Z_2-extension of certain real quadratic fields”, arXiv:2410.17458 (2024).

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