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Sylvester Eriksson-Bique

Publications and source records attributed to Sylvester Eriksson-Bique.

48 records · Page 3Linked to original sources

Infinitesimal splitting for spaces with thick curve families and Euclidean embeddings

We study metric measure spaces that admit "thick" families of rectifiable curves or curve fragments, in the form of Alberti representations or curve families of positive modulus. We show that such spaces cannot be bi-Lipschitz embedded into any Euclidean space unless they admit some "infinitesimal splitting": their tangent spaces are bi-Lipschitz equivalent to product spaces of the form $Z\times \mathbb{R}^k$ for some $k\geq 1$. We also provide applications to conformal dimension and give new proofs of some previously known non-embedding results.

math.MG↗

Thin Loewner carpets and their quasisymmetric embeddings in $S^2$

A carpet is a metric space which is homeomorphic to the standard Sierpiński carpet in $\mathbb{R}^2$, or equivalently, in $S^2$. A carpet is called thin if its Hausdorff dimension is $<2$. A metric space is called Q-Loewner if its $Q$-dimensional Hausdorff measure is Q-Ahlfors regular and if it satisfies a $(1,Q)$-Poincaré inequality. As we will show, $Q$-Loewner planar metric spaces are always carpets, and admit quasisymmetric embeddings into the plane. In this paper, for every pair $(Q,Q')$, with $1<Q<Q'< 2$ we construct infinitely many pairwise quasi-symmetrically distinct $Q$-Loewner carpets $X$ which admit explicit snowflake embeddings, $f: X\to S^2$, for which the image, $f(X)$, admits an explicit description and is $Q'$-Ahlfors regular. In particular, these $f$ are quasisymmetric embeddings. By a result of Tyson, the Hausdorff dimension of a Loewner space cannot be lowered by a quasisymmetric homeomorphism. By definition, this means that the carpets $X$ and $f(X)$ realize their conformal dimension. Each of images $f(X)$ can be further uniformized via post composition with a quasisymmetric homeomorphism of $S^2$, so as to yield a circle carpet and also a square carpet. Our Loewner carpets $X$ are constructed via what we call an admissable quotiented inverse system. This mechanism extends the inverse limit construction for PI spaces given in \cite{cheegerkleinerinverse}, which however, does not yield carpets. Loewner spaces are a particular subclass of PI spaces. They have strong rigidity properties which which do not hold for PI spaces in general.

math.MG↗

Self-improvement of weighted pointwise inequalities on open sets

We prove a general self-improvement property for a family of weighted pointwise inequalities on open sets, including pointwise Hardy inequalities with distance weights. For this purpose we introduce and study the classes of $p$-Poincaré and $p$-Hardy weights for an open set $Ω\subset X$, where $X$ is a metric measure space. We also apply the self-improvement of weighted pointwise Hardy inequalities in connection with usual integral versions of Hardy inequalities.

math.CA↗

Asymptotic behavior of BV functions and sets of finite perimeter in metric measure spaces

In this paper, we study the asymptotic behavior of BV functions in complete metric measure spaces equipped with a doubling measure supporting a $1$-Poincaré inequality. We show that at almost every point $x$ outside the Cantor and jump parts of a BV function, the asymptotic limit of the function is a Lipschitz continuous function of least gradient on a tangent space to the metric space based at $x$. We also show that, at co-dimension $1$ Hausdorff measure almost every measure-theoretic boundary point of a set $E$ of finite perimeter, there is an asymptotic limit set $(E)_\infty$ corresponding to the asymptotic expansion of $E$ and that every such asymptotic limit $(E)_\infty$ is a quasiminimal set of finite perimeter. We also show that the perimeter measure of $(E)_\infty$ is Ahlfors co-dimension $1$ regular.

math.MG↗

Regular mappings and non-existence of bi-Lipschitz embeddings for slit carpets

We prove that the "slit carpet" introduced by Merenkov does not admit a bi-Lipschitz embedding into any uniformly convex Banach space. In particular, this includes any Euclidean space $\mathbb{R}^n$, but also spaces such as $L^p$ for $p \in (1,\infty)$. This resolves Question 8 in the 1997 list by Heinonen and Semmes.

math.MG↗

Alternative proof of Keith-Zhong self-improvement and connectivity

We find a new proof for the celebrated theorem of Keith and Zhong that a $(1,p)$-Poincaré inequality self-improves to a $(1,p-ε)$-Poincaré inequality. The paper consists of a novel characterization of Poincaré inequalities and then uses it to give an entirely new proof which is closely related to Muckenhoupt-weights. This new characterization, and the alternative proof, demonstrate a formal similarity between Muckenhoupt-weights and Poincaré inequalities. The proofs we give are short and somewhat more direct. With them we can give the first completely transparent bounds for the quantity of self-improvement and the constants involved. We observe that the quantity of self-improvement is, for large $p$, directly proportional to $p$, and inversely proportional to a power of the doubling constant and the constant in the Poincaré inequality. The proofs can be localized and thus we obtain more transparent proofs of the self-improvement of local Poincaré inequalities.

math.MG↗

Classifying Poincaré Inequalities and the local geometry of RNP-Differentiability Spaces

We characterize complete RNP-differentiability spaces as those spaces which are rectifiable in terms of doubling metric measure spaces satisfying some local $(1, p)$-Poincaré inequalities. This gives a full characterization of spaces admitting a strong form of a differentiability structure in the sense of Cheeger, and provides a partial converse to his theorem. The proof is based on a new `thickening' construction, which can be used to enlarge subsets into spaces admitting Poincaré inequalities. We also introduce a new notion of quantitative connectivity which characterizes spaces satisfying local Poincaré inequalities. This characterization is of independent interest, and has several applications separate from differentiability spaces. We resolve a question of Tapio Rajala on the existence of Poincaré inequalities for the class of $MCP(K, n)$-spaces which satisfy a weak Ricci-bound. We show that deforming a geodesic metric measure space by Muckenhoupt weights preserves the property of possessing a Poincaré inequality. Finally, the new condition allows us to show that many classes of weak, Orlicz and non-homogeneous Poincaré inequalities `self-improve' to classical $(1, q)$-Poincaré inequalities for some $q \in [1,\infty)$, which is related to Keith's and Zhong's theorem on self-improvement of Poincaré inequalities.

math.MG↗

Equivalence of two BV classes of functions in metric spaces, and existence of a Semmes family of curves under a $1$-Poincaré inequality

We consider two notions of functions of bounded variation in complete metric measure spaces, one due to Martio and the other due to Miranda~Jr. We show that these two notions coincide, if the measure is doubling and supports a $1$-Poincaré inequality. In doing so, we also prove that if the measure is doubling and supports a $1$-Poincaré inequality, then the metric space supports a \emph{Semmes family of curves} structure.

math.MG↗

Quantitative Bi-Lipschitz embeddings of bounded curvature manifolds and orbifolds

We construct bi-Lipschitz embeddings into Euclidean space for manifolds and orbifolds of bounded diameter and curvature. The distortion and dimension of such embeddings is bounded by diameter, curvature and dimension alone. Our results also apply for bounded subsets of complete Riemannian manifolds, and complete flat and elliptic orbifolds. Our approach is based on analysing the structure of a bounded curvature manifold at various scales by specializing methods from collapsing theory to a certain class of model spaces.

math.MG↗

Discrete Dubins Paths

A Dubins path is a shortest path with bounded curvature. The seminal result in non-holonomic motion planning is that (in the absence of obstacles) a Dubins path consists either from a circular arc followed by a segment followed by another arc, or from three circular arcs [Dubins, 1957]. Dubins original proof uses advanced calculus; later, Dubins result was reproved using control theory techniques [Reeds and Shepp, 1990], [Sussmann and Tang, 1991], [Boissonnat, Cérézo, and Leblond, 1994]. We introduce and study a discrete analogue of curvature-constrained motion. We show that shortest "bounded-curvature" polygonal paths have the same structure as Dubins paths. The properties of Dubins paths follow from our results as a limiting case---this gives a new, "discrete" proof of Dubins result.

cs.DM↗