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Ronaldo F. de Lima

Publications and source records attributed to Ronaldo F. de Lima.

13 recordsLinked to original sources
arXiv2026

Dynamical Stability of Translating Solitons to Mean Curvature Flow in Hyperbolic Space

We develop the theory of translating solitons for the Mean Curvature Flow (MCF) in hyperbolic space of dimension $n+1\ge 3$. More specifically, we establish that horospheres are dynamically stable as radial graphical solutions to MCF. To that end, we construct rotationally invariant translators analogous to the winglike solitons introduced by Clutterbuck, Schnürer and Schulze, which serve as barriers in an argument based on White's avoidance principle and the strong maximum principle for parabolic PDEs.

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arXiv2025

Isoparametric Hypersurfaces in Products of Simply Connected Space Forms

Let $\mathbb Q_{ε_i}^{n_i}$ denote the simply connected space form of dimension $n_i\ge 2$ and constant sectional curvature $ε_i$. We prove that any connected isoparametric hypersurface of $\mathbb Q_{ε_1}^{n_1}\times\mathbb Q_{ε_2}^{n_2}$ has constant angle function. We then use this property to classify the isoparametric and homogeneous hypersurfaces of $\mathbb Q_{ε_1}^{n_1}\times\mathbb Q_{ε_2}^{n_2}$, $|ε_1|+|ε_2|\ne 0$, that satisfy a one-point condition.

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arXiv2025

Translators to Higher Order Mean Curvature Flows in $\mathbb R^n\times\mathbb R$ and $\mathbb H^n\times\mathbb R$

We consider translators to the extrinsic flows in $\mathbb R^n\times\mathbb R$ and $\mathbb H^n\times\mathbb R$ (called $r$-mean curvature flows or $r$-MCF, for short) whose velocity functions are the higher order mean curvatures $H_r.$ We show that there exist rotational bowl-type and catenoid-type translators to $r$-MCF in both $\mathbb R^n\times\mathbb R$ and $\mathbb H^n\times\mathbb R,$ and also that there exist parabolic and hyperbolic catenoid-type translators to $r$-MCF in $\mathbb H^n\times\mathbb R.$ In addition, we show that there exist Grim Reaper-type translators to Gaussian flow ($n$-MCF) in $\mathbb R^n\times\mathbb R$ and $\mathbb H^n\times\mathbb R$. We also establish the uniqueness of all these translators (together with certain cylinders) among those which are invariant by either rotations or translations (Euclidean, parabolic or hyperbolic). We apply this uniqueness result to classify the translators to $r$-MCF in $\mathbb R^n\times\mathbb R$ and $\mathbb H^n\times\mathbb R$ whose $r$-th mean curvature is constant, as well as those which are isoparametric. Our results extend to the context of $r$-MCF in $\mathbb R^n\times\mathbb R$ and $\mathbb H^n\times\mathbb R$ the existence and uniqueness theorems by Altschuler--Wu (of the bowl soliton) and Clutterbuck--Schnürer--Schulze (of the translating catenoids) in Euclidean space.

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arXiv2024

On Stability and Isoperimetry of Constant Mean Curvature Spheres of $\mathbb H^n\times\mathbb R$ and $\mathbb S^n\times\mathbb R.$

We approach the one-parameter family of rotational constant mean curvature (CMC) spheres of $\mathbb H^n\times\mathbb R$ and $\mathbb S^n\times\mathbb R$ focusing on their stability and isoperimetry properties. We prove that all rotational CMC spheres of $\mathbb H^n\times\mathbb R$ are stable, and that the ones in $\mathbb S^n\times\mathbb R$ with sufficiently small (resp.~large) mean curvature are unstable (resp.~stable). We also show that there exists a one-parameter family of stable CMC rotational spheres in $\mathbb S^n\times\mathbb R$ which are not isoperimetric (i.e., they do not bound isoperimetric regions). We establish the uniqueness of the regions enclosed by the rotational CMC spheres of $\mathbb H^n\times\mathbb R$ as solutions to the isoperimetric problem, filling in a gap in the original proof given by Hsiang and Hsiang. We establish, as well, a sharp upper bound for the volume of the spherical regions of $\mathbb S^n\times\mathbb R$ which are unique solutions to the isoperimetric problem. In essence, all these results come from the fact that the rotational CMC spheres of $\mathbb H^n\times\mathbb R$, and those of $\mathbb S^n\times\mathbb R$ with sufficiently large mean curvature, are nested.

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arXiv2022

Elliptic Weingarten Hypersurfaces of Riemannian Products

Let $M^n$ be either a simply connected space form or a rank-one symmetric space of noncompact type. We consider Weingarten hypersurfaces of $M\times\mathbb R$, which are those whose principal curvatures $k_1,\dots ,k_n$ and angle function $θ$ satisfy a relation $W(k_1,\dots,k_n,θ^2)=0,$ being $W$ a differentiable function which is symmetric with respect to $k_1,\dots, k_n.$ When $\partial W/\partial k_i>0$ on the positive cone of $\mathbb R^n,$ a strictly convex Weingarten hypersurface determined by $W$ is said to be elliptic. We show that, for a certain class of Weingarten functions $W,$ there exist rotational strictly convex Weingarten hypersurfaces of $M\times\mathbb R$ which are either topological spheres or entire graphs over $M.$ We establish a Jellett-Liebmann-type theorem by showing that a compact, connected and elliptic Weingarten hypersurface of either $\mathbb S^n\times\mathbb R$ or $\mathbb H^n\times\mathbb R$ is a rotational embedded sphere. Other uniqueness results for complete elliptic Weingarten hypersurfaces of these ambient spaces are obtained. We also obtain existence results for constant scalar curvature hypersurfaces of $\mathbb S^n\times\mathbb R$ and $\mathbb H^n\times\mathbb R$ which are either rotational or invariant by translations (parabolic or hyperbolic). We apply our methods to give new proofs of the main results by Manfio and Tojeiro on the classification of constant sectional curvature hypersurfaces of $\mathbb S^n\times\mathbb R$ and $\mathbb H^n\times\mathbb R.$

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arXiv2022

Einstein Hypersurfaces of Warped Product Spaces

We consider Einstein hypersurfaces of warped products $I\times_ω\mathbb Q_ε^n,$ where $I\subset\mathbb R$ is an open interval and $\mathbb Q_ε^n$ is the simply connected space form of dimension $n\ge 2$ and constant sectional curvature $ε\in\{-1,0,1\}.$ We show that, for all $c\in\mathbb R$ (resp. $c>0$), there exist rotational hypersurfaces of constant sectional curvature $c$ in $I\times_ω\mathbb H^n$ and $I\times_ω\mathbb R^n$ (resp. $I\times_ω\mathbb S^n$), provided that $ω$ is nonconstant. We also show that the gradient $T$ of the height function of any Einstein hypersurface of $I\times_ω\mathbb Q_ε^n$ (if nonzero) is one of its principal directions. Then, we consider a particular type of Einstein hypersurface of $I\times_ω\mathbb Q_ε^n$ with non vanishing $T$ -- which we call ideal -- and prove that such a hypersurface $Σ$ has either precisely two or precisely three distinct principal curvatures everywhere. We show that, in the latter case, there exist such a $Σ$ for certain warping functions $ω,$ whereas in the former case, $Σ$ is necessarily of constant sectional curvature and rotational, regardless the warping function $ω.$ We also characterize ideal Einstein hypersurfaces of $I\times_ω\mathbb Q_ε^n$ with no vanishing angle function as local graphs on families of isoparametric hypersurfaces of $\mathbb Q_ε^n.$

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arXiv2021

Totally Umbilical Hypersurfaces of Product Spaces

Given a Riemannian manifold $M,$ and an open interval $I\subset\mathbb{R},$ we characterize nontrivial totally umbilical hypersurfaces of the product $M\times I$ -- as well as of warped products $I\times_ωM$ -- as those which are local graphs built on isoparametric families of totally umbilical hypersurfaces of $M.$ By means of this characterization, we fully extend to $\mathbb{S}^n\times\mathbb{R}$ and $\mathbb{H}^n\times\mathbb{R}$ the results by Souam and Toubiana on the classification of totally umbilical hypersurfaces of $\mathbb{S}^2\times\mathbb{R}$ and $\mathbb{H}^2\times\mathbb{R}.$ It is also shown that an analogous classification holds for arbitrary warped products $I\times_ω\mathbb{S}^n$ and $I\times_ω\mathbb{H}^n.$

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arXiv2020

Helicoids and Catenoids in $M\times\mathbb{R}$

Given an arbitrary $C^\infty$ Riemannian manifold $M^n$, we consider the problem of introducing and constructing minimal hypersurfaces in $M\times\mathbb{R}$ which have the same fundamental properties of the standard helicoids and catenoids of Euclidean space $\mathbb{R}^3=\mathbb{R}^2\times\mathbb{R}$. Such hypersurfaces are defined by imposing conditions on their height functions and horizontal sections, and then called $vertical\, helicoids$ and $vertical \, catenoids$. We establish that vertical helicoids in $M\times\mathbb{R}$ have the same fundamental uniqueness properties of the helicoids in $\mathbb{R}^3.$ We provide several examples of vertical helicoids in the case where $M$ is one of the simply connected space forms. Vertical helicoids which are entire graphs of functions on ${\rm Nil}_3$ and ${\rm Sol}_3$ are also presented. We give a local characterization of hypersurfaces of $M\times\mathbb{R}$ which have the gradient of their height functions as a principal direction. As a consequence, we prove that vertical catenoids exist in $M\times\mathbb{R}$ if and only if $M$ admits families of isoparametric hypersurfaces. If so, they can be constructed through the solutions of a certain first order linear differential equation. Finally, we give a complete classification of the hypersurfaces of $M\times\mathbb{R}$ whose angle function is constant.

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arXiv2019

Hypersurfaces of Product Spaces with a Canonical Direction

Consider a complete Riemannian manifold $M^n$ and let $Σ^n$ be an orientable hypersurface of the product manifold $M\times\mathbb{R}$ endowed with its standard product metric $\langle \,,\, \rangle.$ Let $\nablaξ$ denote the gradient of the height function $ξ$ of $Σ.$ In this note, we characterize the hypersurfaces $Σ$ which have $\nablaξ$ as a principal direction. Our approach is based on the work of R. Tojeiro, who considered the case where $M$ is a constant sectional curvature space form.

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arXiv2018

The $n$-dimensional Peano Curve

One of the most startling mathematical discoveries of the nineteen century was the existence of plane-filling curves. As is well known, the first example of such a curve was given by the Italian mathematician Giuseppe Peano in 1890. Subsequently, other examples of plane-filling curves appeared, with some of them having $n$-dimensional analogues. However, the expressions of the coordinates of the Peano curve are not easily extendable to arbitrary $n$ dimensions. In fact, the only known extension of the Peano curve to an $n$-dimensional space-filling curve, made by Stephen Milne in 1982, is rather geometric and makes it difficult to establish basic properties of these curves, as continuity and nowhere differentiability, as well as more advanced properties, as uniform distribution of the coordinate functions. Here, we will introduce in a completely analytical way the $n$-dimensional version of the Peano curve. More precisely, for a given integer $n\ge 2,$ we will define (by means of identities) the $n$ coordinate functions of a continuous and surjective map from a closed interval to the unit $n$-dimensional cube of $\mathbb{R}^n,$ which, for the particular case $n=2,$ agrees with the original Peano curve. With this description, as we shall see, one can easily establish all the properties we mentioned above, and also calculate the Hausdorff dimension of the graphs of the coordinate functions of this curve.

math.GN↗
arXiv2018

Convexity, Rigidity, and Reduction of Codimension of Isometric Immersions into Space Forms

We consider isometric immersions of complete connected Riemannian manifolds into space forms of nonzero constant curvature. We prove that if such an immersion is compact and has semi-definite second fundamental form, then it is an embedding with codimension one, its image bounds a convex set, and it is rigid. This result generalizes previous ones by M. do Carmo and E. Lima, as well as by M. do Carmo and F. Warner. It also settles affirmatively a conjecture by do Carmo and Warner. We establish a similar result for complete isometric immersions satisfying a stronger condition on the second fundamental form. We extend to the context of isometric immersions in space forms a classical theorem for Euclidean hypersurfaces due to Hadamard. In this same context, we prove an existence theorem of hypersurfaces with prescribed boundary and vanishing Gauss-Kronecker curvature. Finally, we show that isometric immersions into space forms which are regular outside the set of totally geodesic points admit a reduction of codimension to one.

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