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Fabrizio Catanese

Publications and source records attributed to Fabrizio Catanese.

At least 19 recordsLinked to original sources
arXiv2026

Genus $2$ pencils on surfaces with $p_g=K^2=1$, envelopes, and conics tangent to plane cubic curves

We consider $(1,1)$-surfaces, namely, minimal compact complex surfaces $S$ with $p_g (S) =K_S^2=1$: for these the bicanonical map is a covering of degree $4$ of the plane $\mathbb{P}^2$. And we answer a question posed by Meng Chen, whether they can contain a genus 2 pencil (this is the standard reason of failure of birationality of the bicanonical map). Our main theorem says that those which admit a genus 2 pencil form an irreducible subvariety of codimension $3$ in their moduli space $\frak M_{[1,1]}$; moreover, the general such surface admits exactly $12$ such pencils. The real fun is to relate this variety to the geometry of pencils of conics in the plane everywhere tangent to a cubic curve and a line. We investigate the corresponding variety $\mathcal{T}$ of triples and provide explicit equations using the classical theory of envelopes: among others, equations given in terms of the Weierstrass normal form of the cubic.

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arXiv2026

A remark on isolated complex hypersurface singularities

This is now an expository note about the following classical problem. Let $(X, \bf 0)$ be the germ of a hypersurface in $(\mathbb C^n,\bf 0)$ with an ordinary singularity of multiplicity $m$ at the origin $\bf 0$. A natural question to ask is whether $X$ and its tangent cone at the origin are analytically isomorphic. The answer is negative in general, in view of a theorem of Kioji Saito. However there is an integer $D(n,m)>m$ such that, given a \emph{regular} homogeneous polynomial $f(x_1,\ldots, x_n)$ of degree $m$ (this means that $\{ f=0\}$ is a smooth hypersurface in $\PP^{n-1}$) then, for all $d\geq D(n,m)$, any convergent power series of the form $g=f+ o(d)$ (here, as usual, $o(d)$ stays for a power series of order at least $d$), defines a germ $\{ g=0\}$ which is analytically equivalent to the germ $\{ f=0\}$. In this note we compute $D(n,m)$ explicitly as $n(m-2)+1$. We also give an extension to the case in which $f$ is a quasihomogeneous polynomial. It was pointed out that the value of $D(n,m)$ was already known by \cite[Exercise 7.31]{D}.

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arXiv2026

On the numerically and cohomologically trivial automorphisms of elliptic surfaces II: $χ(S)>0$

In this second part we study first the group $Aut_{\mathbb Q}(S)$ of numerically trivial automorphisms of an algebraic properly elliptic surface $S$, that is, of a minimal algebraic surface with Kodaira dimension $κ(S)=1$, in the case $χ(S) \geq 1$. Our first surprising result is that, against what has been believed for over 40 years, there exist nontrivial such groups for $p_g(S) >0$. Indeed, we show even that $Aut_{\mathbb Q}(S)$ is always a 2-generated finite abelian group, but there is no absolute upper bound for its cardinality. At any rate, we give explicit and essentially optimal upper bounds for $|Aut_{\mathbb Q}(S)|$ in terms of the numerical invariants of $S$, as $χ(S)$, or the irregularity $q(S)$, or the bigenus $P_2(S)$. Moreover, we reach an almost complete description of the possible groups $Aut_{\mathbb Q}(S)$ and we give effective criteria for such surfaces to have trivial $Aut_{\mathbb Q}(S)$. Our second surprising results concern the quite elusive group $Aut_{\mathbb Z}(S)$ of cohomologically trivial automorphisms; we are able to give the explicit upper bounds for $|Aut_{\mathbb Z}(S)|$ in special cases: 9 when $p_g(S) =0$, and we achieve the sharp upper bound 3 when $S$ (i.e., the pluricanonical elliptic fibration) is isotrivial. Also in the non isotrivial case we produce subtle examples where $Aut_{\mathbb Z}(S)$ is a group of order 2 or 3.

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arXiv2026

Mok tensors and Orbifold Quotients of Bounded symmetric domains without ball factors

In this paper we characterize the compact orbifolds, quotients $ X = \mathcal{D}/ Γ$ of a bounded symmetric domain $\mathcal{D}$ with no higher dimensional ball factor by the action of a discontinuous group $Γ$, as those projective orbifolds with ample orbifold canonical divisor which admit a Mok curvature type tensor of orbifold type and satisfying certain other conditions implying the existence of a finite smooth covering.

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arXiv2026

Genus stabilization for the homology of moduli spaces of orbit-framed curves with symmetries-I

In a previous paper, arXiv:1301.4409, we showed that the moduli space of curves C with a G-symmetry (that is, with a faithful action of a finite group G), having a fixed generalized homological invariant, is irreducible if the genus g' of the quotient curve C' : = C/G satisfies g'>>0. Interpreting this result as stabilization for the 0-th homology group of the moduli space of curves with G-symmetry, we begin here a program for showing genus stabilization for all the homology groups of these spaces, in similarity to the results of Harer for the moduli space of curves. In this first paper we prove homology stabilization for a variant of the moduli space where one G-orbit is tangentially framed.

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arXiv2026

Cohomologically or numerically trivial automorphisms of surfaces of general type

Our main result is the determination of the respective groups $ Aut_\mathbb{Z}(S) $ of cohomologically trivial automorphisms and $ Aut_\mathbb{Q}(S) $ of numerically trivial automorphisms for the reducible fake quadrics, that is, the surfaces $S$ isogenous to a product with $q=p_g=0$. In this way we produce new record winning examples: a surface $S$ with $|Aut_\mathbb{Q}(S)| =192$, and a surface whose cohomology has torsion with nontrivial $ Aut_\mathbb{Z}(S) \cong \mathbb{Z}/2.$

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arXiv2025

Irrational pencils, and characterization of Varieties isogenous to a product, via the Profinite completion of the Fundamental group

We give a very short proof of two Theorems, whose content is outlined in the title, and where $Π_g$ is the fundamental group of a compact complex curve of genus $g$: (1) Theorem 2.1 of the irrational pencil in the profinite version, saying that for a compact Kähler manifold an irrational pencil, that is, a fibration onto a curve of genus $g \geq 2$, corresponds to a surjection of the profinite completion $\widehatπ_1(X) \twoheadrightarrow \widehat{Π_g}$, which satisfies a maximality property; (2) Theorem 1.4 on the characterization of varieties isogenous to a product, profinite version, giving in particular a criterion for $X$ a compact Kähler manifold to be isomorphic to a product of curves of genera at least 2: if and only if $\widehatπ_1(X) \cong \prod_1^n \widehat{Π_{g_i}}$, and some volume or cohomological condition is satisfied. Theorem 1.4 yields a stronger result than the Main Theorem A of a recent article by 5 authors.

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arXiv2025

Odd fake $\mathbb{Q}$ -homology quadrics exist

We show the existence of odd fake $\mathbb{Q}$-homology quadrics, namely of minimal surfaces $S$ of general type which have the same $\mathbb{Q}$-homology as a smooth quadric $Q \cong (\mathbb{P}^1(\mathbb{C}))^2$, but have an odd intersection form on $ H^2(S, \mathbb{Z})/Tors(S)$, where $Tors(S)$ is the Torsion subgroup. Our examples are provided by a special 1-dimensional family of surfaces isogenous to a product of unmixed type.

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arXiv2025

A new coding theory, for normal surfaces, and ADE singularities, I

In this article we extend the theory of the binary codes (the strict code $\mathcal{K}$ and the extended code $\mathcal{K}'$), associated to a projective nodal surface, to a coding theory for normal surfaces, with special consideration of the surfaces with ADE (Rational Double Points) singularities. We define a new theory of generalized labeled codes, establish in the geometric case basic restrictions for the weights of these codes, and some basic inequality. A crucial method that we establish is the extension of the concept of `code shortening' to the case of generalized codes: this is the algebraic counterpart of the geometric notion of a partial smoothing of the singular points, and leads to the concept of ancestors, which we illustrate through several examples.

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arXiv2025

Varieties of Nodal surfaces, coding theory and Discriminants of cubic hypersurfaces. Part 1: Generalities and nodal K3 surfaces. Part 2: Cubic Hypersurfaces, associated discriminants. Part 3: Nodal quintics. Part 4: Nodal sextics

We attach two binary codes to a projective nodal surface (the strict code K and, for even degree d, the extended code K' ) to investigate the `Nodal Severi varieties F(d, n) of nodal surfaces in P^3 of degree d and with n nodes, and their incidence hierarchy, relating partial smoothings to code shortenings. Our first main result solves a question which dates back over 100 years: the irreducible components of F(4, n) are in bijection with the isomorphism classes of their extended codes K', and these are exactly all the 34 possible shortenings of the extended Kummer code K' , and a component is in the closure of another if and only if the code of the latter is a shortening of the code of the former. We extend this result classifying the irreducible components of all nodal K3 surfaces in the same way, and we fully classify their extended codes. In this classification there are some sporadic cases, obtain through projection from a node. For surfaces of degree d=5 in P^3 we determine (with one possible exception) all the possible codes K, and for several cases of K, we show the irreducibility of the corresponding open set of F(5, n), for instance we show the irreducibility of the family of Togliatti quintic surfaces. In the fourth part we show that a `Togliatti-like' description holds for surfaces of degree 6 with the maximum number of nodes= 65: they are discriminants of cubic hypersurfaces in P^6 with 31 (respectively 32) nodes, and we have an irreducible 18-dimensional family of them. For degree d=6, our main result is based on some novel auxiliary results: 1) the study of the half-even sets of nodes on sextic surfaces, 2) the investigation of discriminants of cubic hypersurfaces X, 3) the computer assisted proof that, for n = 65, both codes K, K' are uniquely determined, 4) the description of these codes, relating the geometry of the Barth sextic with the Doro-Hall graph.

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arXiv2025

Manifolds with trivial Chern classes II: Manifolds Isogenous to a Torus Product, coframed Manifolds and a question by Baldassarri

Motivated by a general question addressed by Mario Baldassarri in 1956, we discuss characterizations of the Pseudo-Abelian Varieties introduced by Roth, and we introduce a first new notion, of Manifolds Isogenous to a k-Torus Product: the latter have the last k Chern classes trivial in rational cohomology and vanishing Chern numbers. We show that in dimension 2 the latter class is the correct substitute for some incorrect assertions by Enriques, Dantoni, Roth and Baldassarri: these are the surfaces with $K_X$ nef and $c_2(X)=0 \in H^4(X, \mathbb{Z})$. We observe in the last section, using a construction by Chad Schoen, that such a simple similar picture does not hold in higher dimension. We discuss then, as a class of solutions to Baldassarri's question, manifolds isogenous to projective (respectively: Kähler) manifolds whose tangent bundle or whose cotangent bundle has a trivial subbundle of positive rank. We see that the class of `partially framed' projective manifolds (that is, whose tangent bundle has a trivial subbundle) consists, in the case where $K_X$ is nef, of the Pseudo-Abelian varieties of Roth; while the class of `partially co-framed' projective manifolds is not yet fully understood in spite of the new results that we are able to show here: and we formulate some open questions and conjectures. In the course of the paper we address also the case of more general compact complex Manifolds, introducing the new notions of suspensions over parallelizable Manifolds, of twisted hyperelliptic Manifolds, and we describe the known results under the Kähler assumption.

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arXiv2025

Mori dream spaces and Q-homology quadrics

We show that Shavel type surfaces are fake quadrics of even type which are not Mori dream surfaces, yet there are infinitely many primes $p$ such that the reduction modulo $p$ is a Mori dream surface. We investigate fake quadrics, first concerning the property of being Mori dream surfaces, then we try to determine which surfaces isogenous to a product are fake quadrics of even type.

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arXiv2024

On the cohomologically trivial automorphisms of elliptic surfaces I: $χ(S)=0$

In this first part we describe the group $Aut_{\mathbb{Z}}(S)$ of cohomologically trivial automorphisms of a properly elliptic surface (a minimal surface $S$ with Kodaira dimension $κ(S)=1$), in the initial case $ χ(\mathcal{O}_S) =0$. In particular, in the case where $Aut_{\mathbb{Z}}(S)$ is finite, we give the upper bound 4 for its cardinality, showing more precisely that if $Aut_{\mathbb{Z}}(S)$ is nontrivial, it is one of the following groups: $\mathbb{Z}/2, \mathbb{Z}/3, (\mathbb{Z}/2)^2$. We also show with easy examples that the groups $\mathbb{Z}/2, \mathbb{Z}/3$ do effectively occur. Respectively, in the case where $Aut_{\mathbb{Z}}(S)$ is infinite, we give the sharp upper bound 2 for the number of its connected components.

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arXiv2024

Orbifold Quotients of Symmetric Domains of Tube type

In this paper we characterize the compact orbifolds, quotients $ X = \mathcal{D} /Γ$ of a bounded symmetric domain $ \mathcal{D}$ of tube type by the action of a discontinuous group $Γ$, as those projective orbifolds with ample canonical divisor possessing a slope zero tensor of `orbifold type'.

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arXiv2024

General birationality and Hyperelliptic Theta divisors

We first state a condition ensuring that having a birational map onto the image is an open property for families of irreducible normal non uniruled varieties. We give then some criteria to ensure general birationality for a family of rational maps, via specializations. Among the applications is a new proof of a result obtained jointly with Luca Cesarano: that, for a general pair $(A,X)$ of an (ample) Hypersurface $X$ in an Abelian Variety $A$, the canonical map $Φ_X$ of $X$ is birational onto its image if the polarization given by $X$ is not principal. The proof is also based on a careful study of the Theta divisors of the Jacobians of Hyperelliptic curves, and some related geometrical constructions. We investigate these here also in view of their beauty and of their independent interest, as they lead to a description of the rings of Hyperelliptic theta functions.

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arXiv2024

Orbifold Classifying Spaces and Quotients of complex Tori

In this paper we characterize the quotients $ X = T/G$ of a complex torus $T$ by the action of a finite group $G$ as the Kähler orbifold classifying spaces of the even Euclidean cristallographic groups $Γ$, and we prove other similar and stronger characterizations.

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arXiv2024

Geometric Endomorphisms of the Hesse moduli space of elliptic curves

We consider the geometric map $ \mathfrak C$, called Cayleyan, associating to a plane cubic $E$ the adjoint of its dual curve. We show that $ \mathfrak C$ and the classical Hessian map $ \mathfrak H$ generate a free semigroup. We begin the investigation of the geometry and dynamics of these maps, and of the geometrically special elliptic curves: these are the elliptic curves isomorphic to cubics in the Hesse pencil which are fixed by some endomorphism belonging to the semigroup $\mathcal W(\frak H, \frak C)$ generated by $ \frak H, \frak C$. We point out then how the dynamic behaviours of $ \mathfrak H$ and $ \mathfrak C$ differ drastically. Firstly, concerning the number of real periodic points: for $ \mathfrak H$ these are infinitely many, for $ \mathfrak C$ they are just $4$. Secondly, the Julia set of $ \mathfrak H$ is the whole projective line, unlike what happens for all elements of $\mathcal W (\frak H, \frak C)$ which are not iterates of $ \mathfrak H$.

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