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Luis Montejano

Publications and source records attributed to Luis Montejano.

At least 19 recordsLinked to original sources
arXiv2025

Generalizing quadratic $\mathbb{R}$-Algebraic sets in $\mathbb{CP}^{n}$

Motivated by our study of the complex Banach conjecture, we characterize a complex ellipsoids $\mathcal E$ as compact subsets of $\mathbb C^n$, with the property that every complex line intersect $\mathcal E$ either in a single point or in the complex affine image of the unit disk. This characterization leads to the main interest of this paper. We study the topological behavior of compact subsets of $\mathbb{CP}^n$ with the property that any complex line that intersects them does either at a single point, at the boundary of a complex disk, or along the entire line. In particular, we are interested in quadratic $\R$-algebraic subsets of $\mathbb{CP}^n$.

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arXiv2024

The 10 antipodal pairings of strongly involutive polyhedra

It is known that strongly involutive polyhedra are closely related to self-dual maps where the antipodal function acts as duality isomorphism. Such a family of polyhedra appears in different combinatorial, topological and geometric contexts, and is thus attractive to be studied. In this note, we determine the 10 antipodal pairings among the classification of the 24 self-dual pairings $Dual(G)\rhd Aut(G)$ of self-dual maps G. We also present the orbifold associated to each antipodal pairing and describe explicitly the corresponding fundamental regions. We finally explain how to construct two infinite families of strongly involutive polyhedra (one of them new) by using their doodles and the action of the corresponding orbifolds.

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arXiv2022

An overview of complex ellipsoids

An ellipsoid is the image of a ball under an affine transformation. If this affine transformation is over the complex numbers, we refer to it as a complex ellipsoid. Characterizations of real ellipsoids have received much attention over the years however, characterizations of complex ellipsoids have been studied very little. This paper is a review of what is known about complex ellipsoids from the point of view of convex geometry. In particular, the proof of the Complex Banach Conjecture.

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arXiv2022

Reflections of convex bodies and their sections

The purpose of this paper is to study the reflections of a convex body. In particular, we are interested in orthogonal reflections of its sections that can be extended to reflections of the whole body. For this reason, we need to study the case of a non-spherical ellipsoid, where a surprising structure arises (Section 2). These results allow us to give a new characterization of ellipsoids in terms of their reflections and, on the other hand, to prove a result deeply related to a conjecture due to K. Bezdek.

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arXiv2021

Complex ellipsoids and complex symmetry

Several characterizations of complex ellipsoids among convex bodies in Cn, in terms of their sections and projections are proved. Characterizing complex symmetry in similar terms is an important tool.

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arXiv2021

Convex bodies all whose sections (projections) are equal

The purpose of this paper is to answer the following question: If all hyperplane sections through the origin of a convex body are "equal", is the convex body "equal" to the ball? The meaning of the notion "equal" will change in the course of this paper. Similarly, we are interested in the following problem: If all orthogonal projections of a convex body onto hyperplanes are "equal", is the convex body "equal" to the ball? Topology and convex geometry are deeply interrelated in the solution and understanding of these problems.

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arXiv2021

Peabodies of Constant Width

The purpose of this paper is to describe a new $3$-dimensional family of bodies of constant width that we have called peabodies, obtained from the Reuleaux tetrahedron by replacing a small neighborhood of all six edges with sections of an envelope of spheres. This family contains, in particular, the two Meissner solids and a body with tetrahedral symmetry that we have called Robert's body. Behind the construction of this family lies the classical notion of confocal quadrics discussed, for example, by Hilbert in his famous book. We study confocal quadrics and prove that the distances of an alternating sequence of four points in two confocal quadrics always satisfies a simple equation and use this equation to prove that our bodies have constant width.

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arXiv2021

Self-dual maps II: links and symmetry

In this paper, we investigate representations of links that are either centrally symmetric in $\mathbb{R}^3$ or antipodally symmetric in $\mathbb{S}^3$. By using the notions of antipodally self-dual and antipodally symmetric maps, introduced and studied by the authors, we are able to present sufficient combinatorial conditions for a link $L$ to admit such representations. The latter naturally arises sufficient conditions for $L$ to be amphichiral. We also introduce another (closely related) method yielding again to sufficient conditions for $L$ to be amphichiral. We finally prove that a link $L$, associated to a map $G$, is amphichiral if the self-dual pairing of $G$ is not one of 6 specific ones among the classification of the 24 self-dual pairing $Cor(G) \rhd Aut(G)$.

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arXiv2020

Extremal inscribed and circumscribed complex ellipsoids

We prove that if a convex set in Cn contains two inscribed complex ellipsoid of maximal volume then one is a translate of the other. On the other hand, the circumscribed complex elipsoid of minimal volume is unique. As application we prove the complex analoge of Brunn's characterization of ellipsods.

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arXiv2020

Self-dual Maps I : antipodality

A self-dual map $G$ is said to be \emph{antipodally self-dual} if the dual map $G^*$ is antipodal embedded in $\mathbb{S}^2$ with respect to $G$. In this paper, we investigate necessary and/or sufficient conditions for a map to be antipodally self-dual. In particular, we present a combinatorial characterization for map $G$ to be antipodally self-dual in terms of certain \emph{involutive labelings}. The latter lead us to obtain necessary conditions for a map to be \emph{strongly involutive} (a notion relevant for its connection with convex geometric problems). We also investigate the relation of antipodally self-dual maps and the notion of \emph{ antipodally symmetric} maps. It turns out that the latter is a very helpful tool to study questions concerning the \emph{symmetry} as well as the \emph{amphicheirality} of \emph{links}.

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arXiv2020

On the complex Banach conjecture

The complex conjecture of Stefan Banach states that if V is a Banach space over the complex numbers where for some n, 1<n<dim(V), all of its n-dimensional subspaces are isometric, then V is a Hilbert space. Mikhail Gromov proved it for n even in 1967. Here, we prove it for n congruent to 1 mod 4.

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arXiv2020

Strongly involutive self-dual polyhedra

A polyhedron is a graph $G$ which is simple, planar and 3-connected. In this note, we classify the family of strongly involutive self-dual polyhedra. The latter is done by using a well-known result due to Tutte characterizing 3-connected graphs. We also show that this special class of polyhedra self-duality behaves topologically as the antipodal mapping. These self-dual polyhedra are related with several problems in convex and discrete geometry including the Vázsonyi problem.

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arXiv2020

Convex Bodies with affinely equivalent projections and affine bodies of revolution

Abstract In this paper, we study affine bodies of revolution. This will allow us to prove that a convex body all whose orthogonal $n$-projections are affinely equivalent is an ellipsoid, provided $n\equiv 0,1, 2$ mod $4$, $n>1$ with the possible exemption of $n=133$. Our proof uses convex geometry and topology of compact Lie groups. AMS classification subject: 22E10, 52A05

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