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Dmitri Zaitsev

Publications and source records attributed to Dmitri Zaitsev.

49 records · Page 3Linked to original sources
arXiv2002

Approximation and convergence of formal CR-mappings

Let $M\subset C^N$ be a minimal real-analytic CR-submanifold and $M'\subset C^{N'}$ a real-algebraic subset through points $p\in M$ and $p'\in M'$. We show that that any formal (holomorphic) mapping $f\colon (C^N,p)\to (C^{N'},p')$, sending $M$ into $M'$, can be approximated up to any given order at $p$ by a convergent map sending $M$ into $M'$. If $M$ is furthermore generic, we also show that any such map $f$, that is not convergent, must send (in an appropriate sense) $M$ into the set $E'\subset M'$ of points of D'Angelo infinite type. Therefore, if $M'$ does not contain any nontrivial complex-analytic subvariety through $p'$, any formal map $f$ as above is necessarily convergent.

math.CV↗
arXiv2001

Extension of CR-functions on wedges

Given a wedge V with generic edge in a submanifold M of $C^N$, in general, CR-functions on V do not extend to a wedge in $C^N$ in the direction of each nontrivial value of the Levi form of M as was recently observed by Eastwood and Graham. In this paper we propose an invariant geometric way of selecting those Levi form directions that are responsible for the extension. These are the Levi form directions of the complex tangent vectors, whose complex planes intersect the tangent cone to the wedge in angles larger than $π/2$. We show by several examples the optimality of this criterion. Applications to regularity of CR-functions are also given generalizing the edge-of-the-wedge theorem of Ajrapetyan-Henkin.

math.CV↗
arXiv2001

The equivalence and the embedding problems for CR-structures of any codimension

We give a solution to the equivalence and the embedding problems for smooth CR-submanifolds of complex spaces (and, more generally, for abstract CR-manifolds) in terms of complete differential systems in jet bundles satisfied by all CR-equivalences or CR-embeddings respectively (local and global). For the equivalence problem, the manifolds are assumed to be of finite type and finitely nondegenerate. These are higher order generalizations of the corresponding nondegeneracy conditions for the Levi form. It is shown by a simple example that these nondegeneracy conditions cannot be even slightly relaxed to more general known conditions. In particular, for essentially finite hypersurfaces in $\C^2$, such a complete system may not exist in general. For the embedding problem, the source manifold is assumed to be of finite type and the embeddings to be finitely nondegenerate. Situations are given, where the last condition is automatically satisfied by all CR-embeddings.

math.CV↗
arXiv2000

Equivalences of real submanifolds in complex space

We show that for any real-analytic submanifold M in C^N there is a proper real-analytic subvariety V contained in M such that for any point p in M\V, any real-analytic submanifold M' in C^N, and any point p' in M', the germs of the submanifolds M and M' at p and p' respectively are formally equivalent if and only if they are biholomorphically equivalent. More general results for k-equivalences are also stated and proved.

math.CV↗
arXiv1999

On symmetric Cauchy-Riemann manifolds

A joint generalization of real smooth as well of complex manifolds are the Cauchy-Riemann manifolds. The main objective of the paper is to inroduce a class of symmetric CR manifolds containing both classes of Riemannian and Hermitian symmetric spaces. It turns out that the classical requirement of isolated fixed points for the symmetries is no longer adequate, because it would imply the Levi-flatness. Among all symmetric CR-manifolds we distinguish a large subclass consisting of all Shilov boundaries of bounded symmetric domains. For this class we calculate the polynomial and the rational convex hulls Both hulls are canonically stratified into real-analytic CR-submanifolds such that the (unique) stratum of the highest dimension is complex for the polynomial and Levi-flat for the rational convex hull. It is also proved that the CR-functions extend continuously to the rational convex hull such that the extension is CR on every stratum.

math.CV↗
arXiv1999

Configurations of linear subspaces and rational invariants

We construct a birational equivalence between certain quotients of s-tuples of equidimensional linear subspaces of $C^n$ and some quotients of products of square matrices modulo diagonal conjugations. In particular, we prove the rationality of the quotient space of s-tuples of linear 2-planes in $C^n$ modulo the diagonal $\gl_n(C)$-action . Furthermore, we compute generators of the field of the rational invariants explicitly.

math.AG↗
arXiv1998

Germs of local automorphisms of real-analytic CR structures and analytic dependence on $k$-jets

The topic of the paper is the study of germs of local holomorphisms $f$ between $C^n$ and $C^{n'}$ such that $f(M)\subset M'$ and $df(T^cM)=T^cM'$ for $M\subset C^n$ and $M'\subset C^{n'}$ generic real-analytic CR submanifolds of arbitrary codimensions. It is proved that for $M$ minimal and $M'$ finitely nondegenerate, such germs depend analytically on their jets. As a corollary, an analytic structure on the set of all germs of this type is obtained.

math.CV↗
arXiv1998

Domains of polyhedral type and boundary extensions of biholomorphisms

For $D$, $D'$ analytic polyhedra in $C^n$, it is proven that a biholomorphic mapping $f\colon D\to D'$ extends holomorphically to a dense boundary subset under certain condition of general position. This result is also extended to a more general class of domains with no smoothness condition on the boundary.

math.CV↗
arXiv1995

Actions of groups of birationally extendible automorphisms

We study the actions of a Lie group $G$ by birationally extendible automorphisms on a domain $D\subset C^n$. For a large class of such domains defined by polynomial inequalities, all automorphisms are of this type. In the cases 1) $G$ has finitely many components or 2) the degree of the automorphisms is bounded, we prove that the action of $G$ is projectively linearizable, i.e. there exist a linear representation of $G$ on some $ C^{N+1}$ and a holomorphic $G$-equivariant embedding $i: D\to P^N$, which is a restriction of a rational mapping. As a corollary we obtain as many rational invariant functions as the dimension of generic orbits allows. A hard copy is available from Dmitri.Zaitsev@rz.ruhr-uni-bochum.de

alg-geom↗
arXiv1994

On the automorphism groups of algebraic bounded domains

Let $D$ be a bounded domain in $C^n$. By the theorem of H.~Cartan, the group $Aut(D)$ of all biholomorphic automorphisms of $D$ has a unique structure of a real Lie group such that the action $Aut(D)\times D\to D$ is real analytic. This structure is defined by the embedding $C_v\colon Aut(D)\hookrightarrow D\times Gl_n(C)$, $f\mapsto (f(v), f_{*v})$, where $v\in D$ is arbitrary. Here we restrict our attention to the class of domains $D$ defined by finitely many polynomial inequalities. The appropriate category for studying automorphism of such domains is the Nash category. Therefore we consider the subgroup $Aut_a(D)\subset Aut(D)$ of all algebraic biholomorphic automorphisms which in many cases coincides with $Aut(D)$. Assume that $n>1$ and $D$ has a boundary point where the Levi form is non-degenerate. Our main result is theat the group $Aut_a(D)$ carries a unique structure of an affine Nash group such that the action $Aut_a(D)\times D\to D$ is Nash. This structure is defined by the embedding $C_v\colon Aut_a(D)\hookrightarrow D\times Gl_n(C)$ and is independent of the choice of $v\in D$.

alg-geom↗
arXiv1994

On the linearization of the automorphism groups of algebraic domains

Let $D$ be a domain in $C^n$ and $G$ a topological group which acts effectively on $D$ by holomorphic automorphisms. In this paper we are interested in projective linearizations of the action of $G$, i.e. a linear representation of $G$ in some $C^{N+1}$ and an equivariant imbedding of $D$ into $¶^N$ with respect to this representation. The domains we discuss here are open connected sets defined by finitely many real polynomial inequalities or connected finite unions of such sets. Assume that the group $G$ acts by birational automorphisms. Our main result is the equivalence of the following conditions: 1) there exists a projective linearization, i.e. a linear representation of $G$ in some $\C^{N+1}$ and a biregular imbedding $i\colon ¶^n \hookrightarrow ¶^N$ such that the restriction $i|_D$ is $G$-equivariant. 2) $G$ is a subgroup of a Lie group $\hat G$ of birational automorphisms of $D$ which extends the action of $G$ and has finitely many connected components; 3) $G$ is a subgroup of a Nash group $\hat G$ of birational automorphisms of $D$ which extends the action of $G$ to a Nash action $\hat G\times D\to D$; 4) $G$ is a subgroup of a Nash group $\hat G$ such that the action $G\times D\to D$ extends to a Nash action $\hat G\times D\to D$; 5) the degree of the automorphism $ϕ_g\colon D\to D$

alg-geom↗