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Fabio Vlacci

Publications and source records attributed to Fabio Vlacci.

12 recordsLinked to original sources
arXiv2026

A note on irreducible slice algebraic sets

In this short note we prove that if $I$ is a right radical and quasi prime ideal in the ring of quaternionic slice regular polynomials, then the symmetrization $\mathbb S_{V_c(I)}$ is an irreducible algebraic set, where $V_c(I)$ is the set of common zeros with commuting components of polynomials in $I$. Combining this fact with the results proved in our previous paper [3], we obtain that for $I$ radical, $V_c(I)$ is irreducible if and only if $I$ is quasi prime.

math.AG↗
arXiv2025

On the irreducibility of slice algebraic sets

In the present paper we investigate the relations between irreducible slice algebraic sets in $\mathbb{H}^n$ and quasi prime right ideals of the ring of slice regular polynomials in $n$ quaternionic variables. We provide algebraic conditions on right ideals of slice regular polynomials which guarantee the irreducibility of the corresponding slice algebraic sets and show that radical ideals associated with irreducible slice algebraic sets are quasi prime. Furthermore we establish that this correspondence is an equivalence in the case of principal right ideals.

math.AG↗
arXiv2024

Vanishing of quaternionic cohomology groups and applications

We present solutions to additive and multiplicative Cousin problems formulated on an axially symmetric domain $\Omega \subset \mathbb H$ for slice--regular functions starting from the solutions for subclasses, namely slice--regular slice--preserving functions and functions in a given vectorial class. Consequently, we prove the vanishing of the corresponding cohomology groups with respect to axially symmetric open coverings (Theorems 1.1, 4.1, 4.2). The primary tool used in the proofs of these theorems is the existence of quaternionic Cartan coverings and Cartan's splitting lemmas. As an application, we prove a jet interpolation theorem (Theorem 1.2) and show that every divisor is principal (Theorem 5.1).

math.CV↗
arXiv2024

Quaternionic Cartan coverings and applications

We present the topological foundations for the solvability of Multiplicative Cousin problems formulated on an axially symmetric domain $\Omega \subset \mathbb H.$ In particular, we provide a geometric construction of quaternionic Cartan coverings, which are generalizations of (complex) Cartan coverings as presented in Section 4 of [FP]. Because of the requirements of symmetry inherent to the domains of definition of quaternionic regular functions, the existence of quaternionic Cartan coverings of $\Omega$ is not a consequence of the existence of complex Cartan coverings because, for the latter, there are no requirements for the symmetries with respect to the real axis. Due to the real axis's special, also the covering restricted to $\Omega \cap \mathbb R$ must have additional properties. All these required properties were achieved by starting from a particular symmetric tiling of the symmetric set $\Omega \cap (\mathbb R + i\mathbb R)$. Finally, we apply these results to prove the vanishing of 'antisymmetric' cohomology groups of planar symmetric domains for $n \geq 2$.

math.CV↗
arXiv2024

A Strong Version of the Hilbert Nullstellensatz for slice regular polynomials in several quaternionic variables

In this paper we prove a strong version of the Hilbert Nullstellensatz in the ring $\mathbb H[q_1,\ldots,q_n]$ of slice regular polynomials in several quaternionic variables. Our proof deeply depends on a detailed analysis of the common zeros of slice regular polynomials which belong to an ideal in $\mathbb H[q_1,\ldots,q_n]$. This study motivates the introduction of a new notion of algebraic set in the quaternionic setting, which allows us to define a Zariski-type topology on $\mathbb H^n$.

math.CV↗
arXiv2023

On a continuation of quaternionic and octonionic logarithm along curves and the winding number

This paper focuses on the problem of finding a continuous extension of the hypercomplex logarithm along a path. While a branch of the complex logarithm can be defined in a small open neighbourhood of a strictly negative real point, no continuous branch of the hypercomplex logarithm can be defined in any open set $A\subset \mathbb K\setminus \{0\}$ which contains a strictly negative real point $x_0$ (here $\mathbb K$ represents the algebra of quaternions or octonions). To overcome these difficulties, we introduced the logarithmic manifold $\mathscr E_\mathbb K^+$ and then showed that if $q\in\mathbb K,\ q=x+Iy$ then $E(x+Iy) %= (\exp (x + Iy), Iy) = (\exp x \cos y + I\exp x \sin y, Iy)$ is an immersion and a diffeomorphism between $\mathbb K$ and $\mathscr E_\mathbb K^+$. In this paper, we consider lifts of paths in $\mathbb K\setminus\{0\}$ to the logarithmic manifold $\mathscr{E}^+_\mathbb K$; even though $\mathbb K \setminus \{0\}$ is simply connected, in general, given a path in $\mathbb K \setminus \{0\}$, the existence of a lift of this path to $\mathscr{E}^+_\mathbb K$ is not guaranteed. There is an obvious equivalence between the problem of lifting a path in $\mathbb K \setminus \{0\}$ and the one of finding a continuation of the hypercomplex logarithm $\log_{\mathbb K}$ along this path.

math.CV↗
arXiv2021

On a definition of logarithm of quaternionic functions

For a slice--regular quaternionic function $f,$ the classical exponential function $\exp f$ is not slice--regular in general. An alternative definition of exponential function, the $*$-exponential $\exp_*$, was given: if $f$ is a slice--regular function, then $\exp_*(f)$ is a slice--regular function as well. The study of a $*$-logarithm $\log_*(f)$ of a slice--regular function $f$ becomes of great interest for basic reasons, and is performed in this paper. The main result shows that the existence of such a $\log_*(f)$ depends only on the structure of the zero set of the vectorial part $f_v$ of the slice--regular function $f=f_0+f_v$, besides the topology of its domain of definition. We also show that, locally, every slice--regular nonvanishing function has a $*$-logarithm and, at the end, we present an example of a nonvanishing slice--regular function on a ball which does not admit a $*$-logarithm on that ball.

math.CV↗
arXiv2021

Slice conformality and Riemann manifolds on quaternions and octonions

In this paper we establish quaternionic and octonionic analogs of the classical Riemann surfaces. The construction of these manifolds has nice peculiarities and the scrutiny of Bernhard Riemann approach to Riemann surfaces, mainly based on conformality, leads to the definition of slice conformal or slice isothermal parameterization of quaternionic or octonionic Riemann manifolds. These new classes of manifolds include slice regular quaternionic and octonionic curves, graphs of slice regular functions, the $4$ and $8$ dimensional spheres, the helicoidal and catenoidal $4$ and $8$ dimensional manifolds. Using appropriate Riemann manifolds, we also give a unified definition of the quaternionic and octonionic logarithm and $n$-th root function.

math.CV↗
arXiv2018

On a class of automorphisms in $\mathbb{H}^2$ which resemble the property of preserving volume

We give a possible extension for shears and overshears in the case of two non commutative (quaternionic) variables in relation with the associated vector fields and flows. We present a possible definition of volume preserving automorphisms, even though there is no quaternionic volume form on $\mathbb{H}^2$ . Using this, we determine a class of quaternionic automorphisms for which the Ander- sen-Lempert theory applies. Finally, we exhibit an example of a quaternionic automor- phism, which is not in the in the closure of the set of finite compositions of volume preserving quaternionic shears.

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