João P. dos Santos | Searcharxiv

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 $\mathbb H^n\times\mathbb R.$

math.DG↗

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 $\mathbb Q_ε^n.$

math.DG↗