arXiv subjects
Publications and source records attributed to M. S. Baouendi.
We consider a Cauchy problem for an overdetermined system of PDEs, and give necessary and sufficient conditions for solvability of this Cauchy problem for all data. As an application, we find all real tube hypersurfaces in complex space whose Levi number is maximal.
Let $Q^N_l\subset \bC\bP^{N+1}$ denote the standard real, nondegenerate hyperquadric of signature $l$ and $M\subset \bC^{n+1}$ a real, Levi nondegenerate hypersurface of the same signature $l$. We shall assume that there is a holomorphic mapping $H_0\colon U\to \bC\bP^{N_0+1}$, where $U$ is some neighborhood of $M$ in $\bC^{n+1}$, such that $H_0(M)\subset Q^{N_0}_l$ but $H(U)\not\subset Q^{N_0}_l$. We show that if $N_0-n<l$ then, for any $N\geq N_0$, any holomorphic mapping $H\colon U\to \bC\bP^{N+1}$ with $H(M)\subset Q^{N}_l$ and $H(U)\not\subset Q^{N_0}_l$ must be the standard linear embedding of $Q^{N_0}_l$ into $Q^N_l$ up to conjugation by automorphisms of $Q^{N_0}_l$ and $Q^N_l$.
In this paper, we consider holomorphic mappings between real hypersurfaces in different dimensional complex spaces. We give a number of conditions that imply that such mappings are transversal to the target hypersurface at most points.
It is shown that a germ of a holomorphic mapping sending a real-analytic generic submanifold of finite type into another is determined by its projection on the Segre variety of the target manifold. A necessary and sufficient condition is given for a germ of a mapping into the Segre variety of the target manifold to be the projection of a holomorphic mapping sending the source manifold into the target. An application to the biholomorphic equivalence problem is also given.
This paper shows that an arbitrary generic submanifold in a complex manifold can be deformed into a 1-parameter family of generic submanifolds satisfying strong nondegeneracy conditions. The proofs use a careful analysis of the jet spaces of embeddings satisfying certain nondegeneracy properties, and also make use of the Thom transversality theorem, as well as the stratification of real-algebraic sets. Optimal results on the order of nondegeneracy are given.
In this paper, we study formal mappings between smooth generic submanifolds in multidimensional complex space and establish results on finite determination, convergence and local biholomorphic and algebraic equivalence. Our finite determination result gives sufficient conditions to guarantee that a formal map as above is uniquely determined by its jet at a point of a preassigned order. For real-analytic generic submanifolds, we prove convergence of formal mappings under appropriate assumptions and also give natural geometric conditions to assure that if two germs of such submanifolds are formally equivalent, then they are necessarily biholomorphically equivalent. If the submanifolds are moreover real-algebraic, we address the question of deciding when biholomorphic equivalence implies algebraic equivalence. In particular, we prove that if two real-algebraic hypersurfaces in $\C^N$ are biholomorphically equivalent, then they are in fact algebraically equivalent. All the results are first proved in the more general context of ``reflection ideals" associated to formal mappings between formal as well as real-analytic and real-algebraic manifolds.
Iterated Segre mappings of real analytic generic submanifolds in complex space have been an essential tool in the study of holomorphic, formal, and CR mappings between such manifolds. In this paper we present a theory of iterated Segre mappings for smooth or formal submanifolds. In particular, we characterize finite type in terms of the rank of the iterated Segre mappings. The approach given here is new, simplifies proofs, and extends results previously known for the real analytic case.
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.
It is shown that a formal mapping between two real-analytic hypersurfaces in complex space is convergent provided that neither hypersurface contains a nontrivial holomorphic variety. For higher codimensional generic submanifolds, convergence is proved e.g. under the assumption that the source is of finite type, the target does not contain a nontrivial holomorphic variety, and the mapping is finite. Finite determination (by jets of a predetermined order) of formal mappings between smooth generic submanifolds is also established.
We consider CR submersive mappings between generic submanifolds in complex space. We show that, under suitable conditions on the manifolds, there is an integer k such that any jet of the CR mapping at a given point is a rational function of its k-jet at that point. As a consequence, it is shown that the stability group of a (suitably nondegenerate) real-analytic generic submanifold is a real algebraic Lie group. Moreover, it is shown that a formal equivalence between two such real-analytic submanifolds is necessarily convergent.
Let $M$ be a real analytic hypersurface in $\bC^N$ which is finitely nondegenerate, a notion that can be viewed as a generalization of Levi nondegenerate, at $p_0\in M$. We show that if $M'$ is another such hypersurface and $p'_0\in M'$, then the set of germs at $p_0$ of biholomorphisms $H$ with $H(M)\subset M'$ and $H(p_0)=p'_0$, equipped with its natural topology, can be naturally embedded as a real analytic submanifold in the complex jet group of $\bC^N$ of the appropriate order. We also show that this submanifold is defined by equations that can be explicitly computed from defining equations of $M$ and $M'$. Thus, $(M,p_0)$ and $(M',p'_0)$ are biholomorphically equivalent if and only if this (infinite) set of equations in the complex jet group has a solution. Another result obtained in this paper is that any invertible formal map $H$ that transforms $(M,p_0)$ to $(M',p'_0)$ is convergent. As a consequence, $(M,p_0)$ and $(M',p'_0)$ are biholomorphically equivalent if and only if they are formally equivalent.
In this paper we prove a general result of the ``Hopf lemma'' type for CR mappings, with nonidentically vanishing Jacobians, between real hypersurfaces in C^n with smooth or real analytic boundaries. Applications of this result to finiteness and holomorphic extendibility of such mappings are also given. The novelty here is that we make no assumption on the nonflatness of the mapping or its Jacobian, nor do we assume that the hypersurfaces are pseudoconvex or minimally convex.
In this paper we shall give sufficient conditions for local CR diffeomorphisms between two real analytic submanifolds of $\Bbb C^N$ to be determined by finitely many derivatives at finitely many points. These conditions will also be shown to be necessary in model cases. We shall also show that under the same conditions, the Lie algebra of the infinitesimal CR automorphisms at a point is finite dimensional.
We give conditions under which a germ of a holomorphic mapping in $\Bbb C^N$, mapping an irreducible real algebraic set into another of the same dimension, is actually algebraic. Let $A\subset \bC^N$ be an irreducible real algebraic set. Assume that there exists $\po \in A$ such that $A$ is a minimal, generic, holomorphically nondegenerate submanifold at $\po$. We show here that if $H$ is a germ at $p_1 \in A$ of a holomorphic mapping from $\bC^N$ into itself, with Jacobian $H$ not identically $0$, and $H(A)$ contained in a real algebraic set of the same dimension as $A$, then $H$ must extend to all of $\bC^N$ (minus a complex algebraic set) as an algebraic mapping. Conversely, we show that for any ``model case'' (i.e., $A$ given by quasi-homogeneous real polynomials), the conditions on $A$ are actually necessary for the conclusion to hold.
We prove that if $M$ and $M'$ are algebraic hypersurfaces in $ C^ N$, i.e. both defined by the vanishing of real polynomials, then any sufficiently smooth CR mapping with Jacobian not identically zero extends holomorphically provided the hypersurfaces are holomorphically nondegenerate . Conversely, we prove that holomorphic nondegeneracy is necessary for this property of CR mappings to hold. For the case of unequal dimensions, we also prove that if $M$ is an algebraic hypersurface in $ C^N$ which does not contain any complex variety of positive codimension and $M'$ is the sphere in $ C^{N+1 }$ , then extendability holds for all CR mappings with certain minimal a priori regularity. Theorem A. Let $M$ and $M'$ be two algebraic hypersurfaces in $C^N$ and assume that $M$ is connected and holomorphically nondegenerate. If $H$ is a smooth CR mapping from $M$ to $M'$ with $ Jac H \not\equiv 0$, where $Jac H$ is the Jacobian determinant of $H$, then $H$ extends holomorphically in an open neighborhood of $M$ in $ C^N$. A recent example given by Ebenfelt shows that the conclusion of Theorem A need not hold if $M$ is real analytic, but not algebraic. Theorem B. Let $M$ be a connected real analytic hypersurface in $C^N$ which is holomorphically degenerate at some point $p_1$. Let $p_0 \in M$ and suppose there exists a germ at $p_0$ of a smooth CR function on $M$ which does not extend holomorphically to any full neighborhood of $p_0$ in $C^N$. Then there exists a germ at $p_0$ of a smooth CR diffeomorphism from $M$ into itself, fixing $p_0$, which does not extend holomorphically to any neighborhood of $p_0$ in $C^N$. Theorem C. Let $M\subset C^N$ be an algebraic hypersurface. Assume that there is no nontrivial complex analytic variety contained in $M$ through $p_0 \in M$, and let $m=m_{p_0}$ be the D'Angelo type. If $H: M \to S^{2N+1}\subset C^{N+1}$ is a CR map of class $C^m$, where $S^{2N+1}$ denotes the boundary of the unit ball in $C^{N+1 }$, then $H$ admits a holomorphic extension in a neighborhood of $p_0$.