arXiv subjects

Alberto Saracco

Publications and source records attributed to Alberto Saracco.

At least 19 recordsLinked to original sources

arXiv2026

Weak elastic energy of rectifiable curves in Riemannian surfaces

We introduce a weak elastic energy for rectifiable curves on compact orientable smooth Riemannian surfaces without boundary. The energy is defined by relaxation starting from a notion of $p$-rotation of inscribed geodesic polygonals, that is obtained by a local construction in normalized isothermal coordinates. For every exponent $p>1$, the resulting relaxed functional detects precisely the intrinsic second-order Sobolev regularity of the arc-length parameterization of the curve. Furthermore, when the relaxed energy is finite, it agrees with the integral of the $p$-power of the geodesic curvature.

math.DG↗

arXiv2025

Weak elastic energy of rectifiable curves in the sphere

We introduce for any exponent $p>1$ the $p$-curvature functional for rectifiable curves in the two-dimensional sphere. We prove that this functional is finite and agrees with the integral of the geodesic curvature raised to the power $p$ on curves whose arc length parameterization is in the Sobolev class $W^{2,p}$.

math.DG↗

arXiv2025

The fundamental theorem of the local theory for non-smooth curves

We extend the classical fundamental theorem of the local theory of smooth curves to a wider class of non-smooth data. Curvature and torsion are prescribed in terms of the distributional derivative measures of two given functions of bounded variation. The essentially unique non-smooth curve solution has both finite total curvature and total absolute torsion. In case of continuous data, we preliminarly discuss a more general problem involving a linear system of distributional derivative equations.

math.DG↗

arXiv2023

Escaping Fatou components with disjoint hyperbolic limit sets

We construct automorphisms of $\mathbb{C}^2$ with a cycle of escaping Fatou components, on which there are exactly two limit functions, both of rank 1. On each such Fatou component, the limit sets for these limit functions are two disjoint hyperbolic subsets of the line at infinity.

math.DS↗

arXiv2023

The geodesic total curvature of spherical curves

The geodesic total curvature of rectifiable spherical curves is analyzed. We extend to the case of high dimension spheres the explicit formula that holds true for curves supported into the 2-sphere. For this purpose, we take advantage of some new integral-geometric formulas concerning both the Euclidean and geodesic total curvature of spherical curves.

math.DG↗

arXiv2022

Weak elastic energy of irregular curves

A weak notion of elastic energy for (not necessarily regular) rectifiable curves in any space dimension is proposed. Our $p$-energy is defined through a relaxation process, where a suitable $p$-rotation of inscribed polygonals is adopted. The discrete $p$-rotation we choose has a geometric flavor: a polygonal is viewed as an approximation to a smooth curve and hence its discrete curvature is spread out into a smooth density. For any exponent $p$ greater than one, the $p$-energy is finite if and only if the arc-length parameterization of the curve has a second order summability with the same growth exponent. In that case, moreover, the energy agrees with the natural extension of the integral of the $p$-th power of the scalar curvature. Finally, a comparison with other definitions of discrete curvatures is discussed.

math.DG↗

arXiv2021

The total intrinsic curvature of curves in Riemannian surfaces

We deal with irregular curves contained in smooth, closed, and compact surfaces. For curves with finite total intrinsic curvature, a weak notion of parallel transport of tangent vector fields is well-defined in the Sobolev setting. Also, the angle of the parallel transport is a function with bounded variation, and its total variation is equal to an energy functional that depends on the "tangential" component of the derivative of the tantrix of the curve. We show that the total intrinsic curvature of irregular curves agrees with such an energy functional. By exploiting isometric embeddings, the previous results are then extended to irregular curves contained in Riemannian surfaces. Finally, the relationship with the notion of displacement of a smooth curve is analyzed.

math.DG↗

arXiv2021

Weak curvatures of irregular curves in high dimension Euclidean spaces

We deal with a robust notion of weak normals for a wide class of irregular curves defined in Euclidean spaces of high dimension. Concerning polygonal curves, the discrete normals are built up through a Gram-Schmidt procedure applied to consecutive oriented segments, and they naturally live in the projective space associated to the Gauss hyper-sphere. By using sequences of inscribed polygonals with infinitesimal modulus, a relaxed notion of total variation of the $j$-th normal to a generic curve is then introduced. For smooth curves satisfying the Jordan system, in fact, our relaxed notion agrees with the length of the smooth $j$-th normal. Correspondingly, a good notion of weak $j$-th normal of irregular curves with finite relaxed energy is introduced, and it turns out to be the strong limit of any sequence of approximating polygonals. The length of our weak normal agrees with the corresponding relaxed energy, for which a related integral-geometric formula is also obtained. We then discuss a wider class of smooth curves for which the weak normal is strictly related to the classical one, outside the inflection points. Finally, starting from the first variation of the length of the weak $j$-th normal, a natural notion of curvature measure is also analyzed.

math.DG↗

arXiv2021

Is math useful?

"Is math useful?" might sound as a trick question. And it is. Of course math is useful, we live in a data-filled world and every aspect of life is totally entwined with math applications, both trivial and subtle applications, of both basic and advanced math. But we need to ask once again that question, in order to truly understand what is math useful for and what being useful means. Moreover, is it knowledge of math useful for a class of specialists, or for political leaders or for all people at large? Being more on a concrete level, why does math need to have a central role in education? Each section will be titled by a question. And each section will not give an answer, but -- at least I hope -- provide some food for tought to the reader, in order to try to come up with his or her own answers. I feel that these kind of questions are at home in a book devoted to the interplays between mathematics and culture: what is the space we should give to math in culture and what is math's role in becoming a complete citizen?

math.HO↗

arXiv2020

The pluricomplex Poisson kernel for strongly pseudoconvex domains

In this paper we introduce, via a Phragmen-Lindelöf type theorem, a maximal plurisubharmonic function in a strongly pseudoconvex domain. We call such a function the {\sl pluricomplex Poisson kernel} because it shares many properties with the classical Poisson kernel of the unit disc. In particular, we show that such a function is continuous, it is zero on the boundary except at one boundary point where it has a non-tangential simple pole, and reproduces pluriharmonic functions. We also use such a function to obtain a new "intrinsic" version of the classical Julia's Lemma and Julia-Wolff-Carathéodory Theorem.

math.CV↗

arXiv2020

Invariant escaping Fatou components with two rank 1 limit functions for automorphisms of $\mathbb{C}^2$

We construct automorphisms of $\mathbb{C}^2$, and more precisely transcendental Hénon maps, with an invariant escaping Fatou component which has exactly two distinct limit functions, both of (generic) rank 1. We also prove a general growth lemma for the norm of points in orbits belonging to invariant escaping Fatou components for automorphisms of the form $F(z,w)=(g(z,w),z)$ with $g(z,w):\mathbb{C}^2\rightarrow\mathbb{C}$ holomorphic.

math.DS↗

arXiv2020

Bounded variation and relaxed curvature of surfaces

We consider a relaxed notion of energy of non-parametric codimension one surfaces that takes account of area, mean curvature, and Gauss curvature. It is given by the best value obtained by approximation with inscribed polyhedral surfaces. The BV and measure properties of functions with finite relaxed energy are studied. Concerning the total mean and Gauss curvature, the classical counterexample by Schwarz-Peano to the definition of area is also analyzed.

math.DG↗

arXiv2020

The weak Frenet frame of non-smooth curves with finite total curvature and absolute torsion

We deal with a notion of weak binormal and weak principal normal for non-smooth curves of the Euclidean space with finite total curvature and total absolute torsion. By means of piecewise linear methods, we first introduce the analogous notation for polygonal curves, where the polarity property is exploited, and then make use of a density argument. Both our weak binormal and normal are rectifiable curves which naturally live in the projective plane. In particular, the length of the weak binormal agrees with the total absolute torsion of the given curve. Moreover, the weak normal is the vector product of suitable parameterizations of the tangent indicatrix and of the weak binormal. In the case of smooth curves with positive curvature, the weak binormal and normal yield (up to a lifting) the classical notions of binormal and normal.

math.DG↗

arXiv2020

Dr. Strangelove or: how I learned to stop worrying and love the citations

Citations are getting more and more important in the career of a researcher. But how to use them in the best possible way? This is a satirical paper, showing a bad trend currently happening in citation trends, due to intensive use of citation metrics. I am putting this on the arXiv and on Researchgate. Should you be interested to publish this paper on a journal of which you are editor, let me know.

cs.DL↗

arXiv2019

A discrete districting plan

The outcome of elections is strongly dependent on the districting choices, making thus possible (and frequent) the gerrymandering phenomenon, i.e.\ politicians suitably changing the shape of electoral districts in order to win the forthcoming elections. While so far the problem has been treated using continuous analysis tools, it has been recently pointed out that a more reality-adherent model would use the discrete geometry of graphs or networks. Here we propose a parameter-dependent discrete model for choosing an "optimal" districting plan. We analyze several properties of the model and lay foundations for further analysis on the subject.

math.OC↗

arXiv2017

Carleson measures for Hardy and Bergman spaces in the quaternionic unit ball

We study a characterization of slice Carleson measures and of Carleson measures for the both the Hardy spaces $H^p(\mathbb B)$ and the Bergman spaces $\mathcal A^p(\mathbb B)$ of the quaternionic unit ball $\mathbb B$. In the case of Bergman spaces, the characterization is done in terms of the axially symmetric completion of a pseudohyperbolic disc in a complex plane. We also show that a characterization in terms of pseudohyperbolic balls is not possible.

math.CV↗

arXiv2016

Discrete sequences in unbounded domains

Discrete sequences with respect to the Kobayashi distance in a strongly pseudoconvex bounded domain $D$ are related to Carleson measures by a formula that uses the Euclidean distance from the boundary of $D$. Thus the speed of escape at the boundary of such sequence has been studied in details for strongly pseudoconvex bounded domain $D$. In this note we show that such estimations completely fail if the domain is not bounded.

math.CV↗

arXiv2013

Non compact boundaries of complex analytic varieties in Hilbert spaces

We treat the boundary problem for complex varieties with isolated singularities, of complex dimension greater than or equal to 3, non necessarily compact, which are contained in strongly convex, open subsets of a complex Hilbert space H. We deal with the problem by cutting with a family of complex hyperplanes in the fashion of [2] and applying the first named author's result for the compact case [13].

math.CV↗