Isolated singularities of mappings with the inverse Poletsky inequality

The manuscript is devoted to the study of mappingswith finite distortion, which have been actively studied recently.We consider mappings satisfying the inverse Poletsky inequality,which can have branch points. Note that mappings with the reversePoletsky inequality include the classes of con\-for\-mal,quasiconformal, and quasiregular mappings. The subject of thisarticle is the question of removability an isolated singularity of amapping. The main result is as follows. Suppose that $f$ is an opendiscrete mapping between domains of a Euclidean $n$-dimensionalspace satisfying the inverse Poletsky inequality with someintegrable majorant $Q.$ If the cluster set of $f$ at some isolatedboundary point $x_0$ is a subset of the boundary of the image of thedomain, and, in addition, the function $Q$ is integrable, then $f$has a continuous extension to $x_0.$ Moreover, if $f$ is finite at$x_0,$ then $f$ is logarithmic H\"{o}lder continuous at $x_0$ withthe exponent $1/n.$

On removal of isolates singularities of open discrete mappings

We study mappings with finite distortion in $\mathbb{R}^n$, $n \geqslant 2$. For the classes of mappings with branching that satisfy modal inequalities we obtain the set of theorems on removal of isolated singularities.

On connection of finite distortion mappings with length distortion in $\mathbb{R}^n$

The present paper is devoted to the investigations of mappings with finite distortion in $\mathbb{R}^n$, $n \geqslant 2$. In the work it is proved that every open discrete mapping with finite distortion by Iwaniec such that the branch set of $f$ is of measure zero is a mapping with finite length distortion provided that the corresponding outer dilatation satisfies the inequality $K_O (x, f) \leqslant K(x)$ a.e., where $K(x) \in L_{loc}^{n-1}(D)$.

Mappings of finite distortion: Size of the branch set

We study the branch set of a mapping between subsets of {\mathbb{R}^{n}}, i.e., the set where a given mapping is not defining a local homeomorphism. We construct several sharp examples showing that the branch set or its image can have positive measure.

On nonhomeomorphic mappings with the inverse Poletsky inequality

As known, the modulus method is one of the most powerful research tools in the theory of mappings. Distortion of modulus has an important role in the study of conformal and quasiconformal mappings, mappings with bounded and finite distortion, mappings with finite length distortion, etc. In particular, an important fact is the lower distortion of the modulus under mappings. Such relations are called inverse Poletsky inequalities and are one of the main objects of our study. The use of these inequalities is fully justified by the fact that the inverse inequality of Poletsky is a direct (upper) inequality for the inverse mappings, if there exist. If the mapping has a bounded distortion, then the corresponding majorant in inverse Poletsky inequality is equal to the product of the maximum multiplicity of the mapping on its dilatation. For more general classes of mappings, a similar majorant is equal to the sum of the values of outer dilatations over all preimages of the fixed point. It the class of quasiconformal mappings there is no significance between the inverse and direct inequalities of Poletsky, since the upper distortion of the modulus implies the corresponding below distortion and vice versa. The situation significantly changes for mappings with unbounded characteristics, for which the corresponding fact does not hold. The most important case investigated in this paper refers to the situation when the mappings have an unbounded dilatation. The article investigates the local and boundary behavior of mappings with branching that satisfy the inverse inequality of Poletsky with some integrable majorant. It is proved that mappings of this type are logarithmically Holder continuous at each inner point of the domain. Note that the Holder continuity is slightly weaker than the classical Holder continuity, which holds for quasiconformal mappings. Simple examples show that mappings of finite distortion are not Lipschitz continuous even under bounded dilatation. Another subject of research of the article is boundary behavior of mappings. In particular, a continuous extension of the mappings with the inverse Poletsky inequality is obtained. In addition, we obtained the conditions under which the families of these mappings are equicontinuous inside and at the boundary of the domain. Several cases are considered: when the preimage of a fixed continuum under mappings is separated from the boundary, and when the mappings satisfy normalization conditions. The text contains a significant number of examples that demonstrate the novelty and content of the results. In particular, examples of mappings with branching that satisfy the inverse Poletsky inequality, have unbounded characteristics, and for which the statements of the basic theorems are satisfied, are given.

Sobolev mappings and moduli inequalities on Carnot groups

We study the mappings that satisfy moduli inequalities on Carnot groups. We prove that the homeomorphisms satisfying the moduli inequalities ($Q$-homeomor\-phisms) with a locally integrable function $Q$ are Sobolev mappings. On this base in the frameworks of the weak inverse mapping theorem, we prove that, on the Carnot groups $\mathbb G,$ the mappings inverse to Sobolev homeomorphisms of finite distortion of the class $W^1_{\nu,\loc}(\Omega;\Omega')$ belong to the Sobolev class $W^1_{1,\loc}(\Omega';\Omega)$.

On boundary extension of one class of mappings in terms of prime ends

Here we consider the classes of mappings of metric spaces that distort the modulus of families of paths similarly to Poletsky inequality. For domains, which are not locally connected at the boundaries, we obtain results on the boundary extension of the indicated mappings. We also investigate the local and global behaviorof mappings in the context of the equicontinuity of their families. The main statements of the article are proved under the condition that the majorant responsible for the distortion of the modulus of the families of paths has a finite mean oscillation at the corresponding points. The results are applicable to well-known classes of conformal and quasiconformal mappings as well as mappings with a finite distortion.

Optimal Extensions of Conformal Mappings from the Unit Disk to Cardioid-Type Domains

The conformal mapping $$f(z)=(z+1)^2 $$f(z)=(z+1)2 from $${\mathbb {D}}$$D onto the standard cardioid has a homeomorphic extension of finite distortion to entire $${\mathbb {R}}^2 .$$R2. We study the optimal regularity of such extensions, in terms of the integrability degree of the distortion and of the derivatives, and these for the inverse. We generalize all outcomes to the case of conformal mappings from $${\mathbb {D}}$$D onto cardioid-type domains.