Coarse infinite-dimensionality of hyperspaces of finite subsets

We consider infinite-dimensional properties in coarse geometry for hyperspaces consisting of finite subsets of metric spaces with the Hausdorff metric. We see that several infinite-dimensional properties are preserved by taking the hyperspace of subsets with at most n points. On the other hand, we prove that, if a metric space contains a sequence of long intervals coarsely, then its hyperspace of finite subsets is not coarsely embeddable into any uniformly convex Banach space. As a corollary, the hyperspace of finite subsets of the real line is not coarsely embeddable into any uniformly convex Banach space. It is also shown that every (not necessarily bounded geometry) metric space with straight finite decomposition complexity has metric sparsification property.

Heat Kernels Estimates for Hermitian Line Bundles on Manifolds of Bounded Geometry

We consider a family of semiclassically scaled second-order elliptic differential operators on high tensor powers of a Hermitian line bundle (possibly, twisted by an auxiliary Hermitian vector bundle of arbitrary rank) on a Riemannian manifold of bounded geometry. We establish an off-diagonal Gaussian upper bound for the associated heat kernel. The proof is based on some tools from the theory of operator semigroups in a Hilbert space, results on Sobolev spaces adapted to the current setting, and weighted estimates with appropriate exponential weights.

Bounded $$H^\infty $$-calculus for a degenerate elliptic boundary value problem

On a manifold X with boundary and bounded geometry we consider a strongly elliptic second order operator A together with a degenerate boundary operator T of the form $$T=\varphi _0\gamma _0 + \varphi _1\gamma _1$$ T = φ 0 γ 0 + φ 1 γ 1 . Here $$\gamma _0$$ γ 0 and $$\gamma _1$$ γ 1 denote the evaluation of a function and its exterior normal derivative, respectively, at the boundary. We assume that $$\varphi _0, \varphi _1\ge 0$$ φ 0 , φ 1 ≥ 0 , and $$\varphi _0+\varphi _1\ge c$$ φ 0 + φ 1 ≥ c , for some $$c>0$$ c > 0 , where either $$\varphi _0,\varphi _1\in C^{\infty }_b(\partial X)$$ φ 0 , φ 1 ∈ C b ∞ ( ∂ X ) or $$\varphi _0=1 $$ φ 0 = 1 and $$\varphi _1=\varphi ^2$$ φ 1 = φ 2 for some $$\varphi \in C^{2+\tau }(\partial X)$$ φ ∈ C 2 + τ ( ∂ X ) , $$\tau >0$$ τ > 0 . We also assume that the highest order coefficients of A belong to $$C^\tau (X)$$ C τ ( X ) and the lower order coefficients are in $$L_\infty (X)$$ L ∞ ( X ) . We show that the $$L_p(X)$$ L p ( X ) -realization of A with respect to the boundary operator T has a bounded $$H^\infty $$ H ∞ -calculus. We then obtain the unique solvability of the associated boundary value problem in adapted spaces. As an application, we show the short time existence of solutions to the porous medium equation.

Uniformization of Cantor sets with bounded geometry

In this note we provide a quasisymmetric taming of uniformly perfect and uniformly disconnected sets that generalizes a result of MacManus [Rev. Mat. Iberoamericana 15 (1999), pp. 267–277] from 2 to higher dimensions. In particular, we show that a compact subset of R n \mathbb {R}^n is uniformly perfect and uniformly disconnected if and only if it is ambiently quasiconformal to the standard Cantor set C \mathcal {C} in R n + 1 \mathbb {R}^{n+1} .