arXiv subjects

Michele Fornea

Publications and source records attributed to Michele Fornea.

11 recordsLinked to original sources

arXiv2026

Plectic Heegner classes

We introduce a new collection of partially global Galois cohomology classes subsuming both plectic Heegner points and mock plectic invariants. The former are recovered as localizations of plectic Heegner classes, while the latter arise as eigenspace projections with respect to a "partial Frobenius"-action. By overcoming some limitations of previous constructions, plectic Heegner classes are expected to provide finer control over the arithmetic of higher rank elliptic curves. We are able to perform our construction via a systematic use of certain automorphic functions whose coefficients are p-adic measures valued in Galois cohomology. As we produce these functions through the uniformization of Shimura curves -- rather than higher dimensional quaternionic Shimura varieties -- our results are compatible with a plectic refinement of Tate's conjectures.

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arXiv2024

Non-Archimedean plectic Jacobians

Plectic Stark-Heegner points were recently introduced to explore the arithmetic of higher rank elliptic curves: the concept was inspired by Nekov\'a\v{r} and Scholl's plectic philosophy, while the construction is based on Bertolini and Darmon's groundbreaking use of the $p$-adic uniformization of Shimura curves to study the Birch-Swinnerton-Dyer conjecture. In this note we give a geometric interpretation of plectic Heegner points using the non-Archimedean uniformization of higher-dimensional quaternionic Shimura varieties. To this end, we define and study a plectic Jacobian functor from a category of Mumford varieties to topological groups extending the classical Jacobian functor on Mumford curves.

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arXiv2023

Iwasawa theory and mock plectic points

We use Iwasawa theory, at a prime $p$ inert in a quadratic imaginary field $K$, to study the arithmetic properties of mock plectic invariants for elliptic curves of rank two. More precisely, under some minor technical assumptions, we prove that the non-vanishing of the mock plectic invariant $\mathcal{Q}_K$ attached to an elliptic curve $E_{/\mathbb{Q}}$ of even analytic rank $r_\mathrm{an}(E/K)\ge2$, and with multiplicative reduction at $p$, implies that the $p$-Selmer rank $r_p(E/K)$ equals $2$. The proof rests on one inclusion of Perrin-Riou's Heegner point main conjecture for elliptic curves with multiplicative reduction at $p$ which we obtain using bipartite Euler systems.

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arXiv2023

Mock plectic points

A $p$-arithmetic subgroup of $\mathrm{SL}_2(\mathbb{Q})$ like the Ihara group $\Gamma := \mathrm{SL}_2(\mathbb{Z}[1/p])$ acts by M\"obius transformations on the Poincar\'e upper half plane $\mathcal{H}$ and on Drinfeld's $p$-adic upper half plane $\mathcal{H}_p := \mathbb{P}_1(\mathbb{C}_p)\setminus\mathbb{P}_1(\mathbb{Q}_p)$. The diagonal action of $\Gamma$ on the product is discrete, and the quotient $\Gamma\backslash(\mathcal{H}_p\times \mathcal{H})$ can be envisaged as a "mock Hilbert modular surface". According to a striking prediction of Nekov\'a$\check{\text{r}}$ and Scholl, the CM points on genuine Hilbert modular surfaces should give rise to "plectic Heegner points" that encode non-trivial regulators attached, notably, to elliptic curves of rank two over real quadratic fields. This article develops the analogy between Hilbert modular surfaces and their mock counterparts, with the aim of transposing the plectic philosophy to the mock Hilbert setting, where the analogous plectic invariants are expected to lie in the alternating square of the Mordell-Weil group of certain elliptic curves of rank two over $\mathbb{Q}$.

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arXiv2023

Plectic Jacobians

Looking for a geometric framework to study plectic Heegner points, we define a collection of abelian varieties - called plectic Jacobians - using the middle degree cohomology of quaternionic Shimura varieties (QSVs). The construction is inspired by the definition of Griffiths' intermediate Jacobians and rests on Nekovar-Scholl's notion of plectic Hodge structures. Moreover, we construct exotic Abel-Jacobi maps sending certain zero-cycles on QSVs to plectic Jacobians.

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arXiv2022

On the algebraicity of polyquadratic plectic points

We establish direct evidence of the arithmetic significance of plectic Stark-Heegner points for elliptic curves of arbitrarily large rank. The main contribution is a proof of the algebraicity of plectic points associated to polyquadratic CM extensions of totally real number fields. Moreover, we relate the non-vanishing of plectic points to analytic and algebraic ranks of elliptic curves.

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arXiv2021

Plectic p-adic invariants

For modular elliptic curves over number fields of narrow class number one, and with multiplicative reduction at a collection of p-adic primes, we define new p-adic invariants. Inspired by Nekovar and Scholl's plectic conjectures, we believe these invariants control the Mordell--Weil group of higher rank elliptic curves and we support our expectations with numerical experiments.

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arXiv2021

Plectic Stark-Heegner points

We propose a conjectural construction of global points on modular elliptic curves over arbitrary number fields, generalizing both the p-adic construction of Heegner points via Cerednik-Drinfeld uniformization and the definition of classical Stark-Heegner points. In alignment with Nekovar and Scholl's plectic conjectures, we expect the non-triviality of these plectic Stark-Heegner points to control the Mordell-Weil group of higher rank elliptic curves. We provide some indirect evidence for our conjectures by showing that higher order derivatives of anticyclotomic p-adic L-functions compute plectic invariants.

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arXiv2020

Hirzebruch-Zagier classes and rational elliptic curves over quintic fields

Conditionally on a conjecture on the \'etale cohomology of Hilbert modular surfaces and some minor technical assumptions, we establish new instances of the equivariant BSD-conjecture in rank $0$ with applications to the arithmetic of rational elliptic curves over quintic fields. The key ingredients are a refinement of twisted triple product $p$-adic $L$-functions, the construction of a compatible collection of Hirzebruch-Zagier cycles and an explicit reciprocity law relating the two.

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arXiv2019

Twisted triple product p-adic L-functions and Hirzebruch-Zagier cycles

Let $L/F$ be a quadratic extension of totally real number fields. For any prime $p$ unramified in $L$, we construct a $p$-adic $L$-function interpolating the central values of the twisted triple product $L$-functions attached to a $p$-nearly ordinary family of unitary cuspidal automorphic representations of $\text{Res}_{L\times F/F}(\text{GL}_{2})$. Furthermore, when $L/\mathbb{Q}$ is a real quadratic number field and $p$ is a split prime, we prove a $p$-adic Gross-Zagier formula relating the value of the $p$-adic $L$-function outside the range of interpolation to the syntomic Abel-Jacobi image of generalized Hirzebruch-Zagier cycles.

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arXiv2019

Growth of the analytic rank of modular elliptic curves over quintic extensions

Given $F$ a totally real field and $E_{/F}$ a modular elliptic curve, we denote by $G_5(E_{/F};X)$ the number of quintic extensions $K$ of $F$ such that the norm of the relative discriminant is at most $X$ and the analytic rank of $E$ grows over $K$, i.e., $r_\mathrm{an}(E/K)>r_\mathrm{an}(E/F)$. We show that $G_5(E_{/F};X)\asymp_{+\infty} X$ when the elliptic curve $E_{/F}$ has odd conductor and at least one prime of multiplicative reduction. As Bhargava, Shankar and Wang \cite{BSW} showed that the number of quintic extensions of $F$ with norm of the relative discriminant at most $X$ is asymptotic to $c_{5,F} X$ for some positive constant $c_{5,F}$, our result exposes the growth of the analytic rank as a very common circumstance over quintic extensions.

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