arXiv subjects

Morena Porzio

Publications and source records attributed to Morena Porzio.

4 recordsLinked to original sources

arXiv2025

On Modified Diagonal Cycles and the Beauville Decomposition of the Ceresa Cycle

Let $C$ be a curve of genus $g \geq 2$, and let $J$ be its Jacobian. The choice of a degree 1 divisor $e$ on $C$ gives an embedding of $C$ into $J$; we denote by $[C]_{}^{e}\in \mathrm{CH}\left( J;\mathbb{Q} \right) $ the class in the Chow group of $J$ defined by its image. It is known that the vanishing of the Ceresa cycle $\mathrm{Cer}(C,e):=[C]^{e} - [-1]_* [C]^e$ is equivalent to both the vanishing of the 1st Beauville component $[C]_{(1)}^e$ and the vanishing of the 3rd Gross--Kudla--Schoen modified diagonal cycle $\Gamma^3(C,e) \in \mathrm{CH}(C^3;\mathbb{Q})$. We extend this result to show that the vanishing of the $s$-th Beauville component $[C]^e_{(s)}$ for $s \geq 1$ is equivalent to the vanishing of the $(s+2)$-nd modified diagonal cycle $\Gamma^{s + 2}(C, e) \in \mathrm{CH}(C^{s+2};\mathbb{Q})$. Moreover, we establish "successive vanishing" results for these cycles. We apply our results to study the rational (non)-triviality of $[C]^{e}_{(s)}$ in the special case $s = 2$. Finally in the $s=1$ case, we show an integral refinement to the original statement, relating the order of torsion of $\mathrm{Cer}(C,e) \in \mathrm{CH}(J;\mathbb{Z})$ to that of $\Gamma^3(C,e) \in \mathrm{CH}(C^3;\mathbb{Z})$.

math.AG↗

arXiv2025

Isotopy invariance and stratified $\mathbb{E}_2$-structure of the Ran Grassmannian

Let $G$ be a complex reductive group. A folklore result asserts the existence of an $\mathbb{E}_2$-algebra structure on the Ran Grassmannian of $G$ over $\mathbb{A}^1_{\mathbb{C}}$, seen as a topological space with the complex-analytic topology. The aim of this paper is to prove this theorem, by establishing a homotopy invariance result: namely, an inclusion of open balls $D' \subset D$ in $\mathbb{C}$ induces a homotopy equivalence between the respective Beilinson--Drinfeld Grassmannians $\mathrm{Gr}_{G, {D'}^n} \hookrightarrow \mathrm{Gr}_{G, D^n}$, for any positive integer $n$. We use a purely algebraic approach, showing that automorphisms of a complex smooth algebraic curve $X$ can be lifted to automorphisms of the associated Beilinson--Drinfeld Grassmannian. As a consequence, we obtain a stronger version of the usual homotopy invariance result: namely, the homotopies can be promoted to equivariant stratified isotopies, where "equivariant" refers to the action of the arc group $\mathrm{L}^+G$ and "stratified" refers to the stratification induced by the Schubert stratification of $\mathrm{Gr}_G$ and the incidence stratification of $\mathbb{C}^n$.

math.AT↗

arXiv2025

Density of algebraic points on products of curves

In this paper, we initiate the systematic study of density of algebraic points on surfaces. We give an effective asymptotic range in which the density degree set has regular behavior dictated by the index. By contrast, in small degree, the question of density is subtle and depends on the arithmetic of the curves. We give several explicit examples displaying these different behaviors, including products of genus $2$ curves with and without dense quadratic points. These results for products of curves have applications to questions about algebraic points on closely related surfaces, such as rank growth on abelian surfaces and bielliptic surfaces.

math.NT↗

arXiv2024

On the Stable Birationality of Hilbert schemes of points on surfaces

The aim of this paper is to study the stable birational type of $Hilb^n_X$, the Hilbert scheme of degree $n$ points on a surface $X$. More precisely, it addresses the question for which pairs of positive integers $(n,n')$ the variety $Hilb^n_X$ is stably birational to $Hilb^{n'}_X$, when $X$ is a surface with irregularity $q(X)=0$. After general results for such surfaces, we restrict our attention to geometrically rational surfaces, proving that there are only finitely many stable birational classes among the $Hilb^n_X$'s. As a corollary, we deduce the rationality of the motivic zeta function $ζ(X,t)$ in $K_0(Var/k)/([\mathbb{A}^1_k])[[t]]$ over fields of characteristic zero.

math.AG↗