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Register a new userOn Convergent Poincare-Moser Reduction for Levi Degenerate Embedded $5$-Dimensional CR Manifolds
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Wei Guo Foo
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Applying Lies theory, we show that any $mathcal{C}^omega$ hypersurface $M^5 subset mathbb{C}^3$ in the class $mathfrak{C}_{2,1}$ carries Cartan-Moser chains of orders $1$ and $2$. Integrating and straightening any order $2$ chain at any point $p in M$ to be the $v$-axis in coordinates $(z, zeta, w = u + i, v)$ centered at $p$, we show that there exists a (unique up to 5 parameters) convergent change of complex coordinates fixing the origin in which $gamma$ is the $v$-axis so that $M = {u=F(z,zeta,overline{z},overline{zeta},v)}$ has Poincare-Moser reduced equation: begin{align} u & = zoverline{z} + tfrac{1}{2},overline{z}^2zeta + tfrac{1}{2},z^2overline{zeta} + zoverline{z}zetaoverline{zeta} + tfrac{1}{2},overline{z}^2zetazetaoverline{zeta} + tfrac{1}{2},z^2overline{zeta}zetaoverline{zeta} + zoverline{z}zetaoverline{zeta}zetaoverline{zeta} & + 2{rm Re} { z^3overline{zeta}^2 F_{3,0,0,2}(v) + zetaoverline{zeta} ( 3,{z}^2overline{z}overline{zeta} F_{3,0,0,2}(v) ) } & + 2{rm Re} { z^5overline{zeta} F_{5,0,0,1}(v) + z^4overline{zeta}^2 F_{4,0,0,2}(v) + z^3overline{z}^2overline{zeta} F_{3,0,2,1}(v) + z^3overline{z}overline{zeta}^2 F_{3,0,1,2}(v) + z^3{overline{zeta}}^3 F_{3,0,0,3}(v) } & + z^3overline{z}^3 {rm O}_{z,overline{z}}(1) + 2{rm Re} ( overline{z}^3zeta {rm O}_{z,zeta,overline{z}}(3) ) + zetaoverline{zeta}, {rm O}_{z,zeta,overline{z},overline{zeta}}(5). end{align} The values at the origin of Pocchiolas two primary invariants are: [ W_0 = 4overline{F_{3,0,0,2}(0)}, quadquad J_0 = 20, F_{5,0,0,1}(0). ] The proofs are detailed, accessible to non-experts. The computer-generated aspects (upcoming) have been reduced to a minimum.
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A complex manifold $X$ is emph{weakly complete} if it admits a continuous plurisubharmonic exhaustion function $phi$. The minimal kernels $Sigma_X^k, k in [0,infty]$ (the loci where are all $mathcal{C}^k$ plurisubharmonic exhaustion functions fail to be strictly plurisubharmonic),introduced by Slodkowski-Tomassini, and the Levi currents, introduced by Sibony, are both concepts aimed at measuring how far $X$ is from being Stein. We compare these notions, prove that all Levi currents are supported by all the $Sigma_X^k$s, and give sufficient conditions for points in $Sigma_X^k$ to be in the support of some Levi current. When $X$ is a surface and $phi$ can be chosen analytic, building on previous work by the second author, Slodkowski, and Tomassini,we prove the existence of a Levi current precisely supported on $Sigma_X^infty$, and give a classification of Levi currents on $X$. In particular,unless $X$ is a modification of a Stein space, every point in $X$ is in the support of some Levi current.
We introduce a new geometrical invariant of CR manifolds of hypersurface type, which we dub the Levi core of the manifold. When the manifold is the boundary of a smooth bounded pseudoconvex domain, we show how the Levi core is related to two other important global invariants in several complex variables: the Diederich--Forn{ae}ss index and the DAngelo class (namely the set of DAngelo forms of the boundary). We also show that the Levi core is trivial whenever the domain is of finite-type in the sense of DAngelo, or the set of weakly pseudoconvex points is contained in a totally real submanifold, while it is nontrivial if the boundary contains a local maximum set. As corollaries to the theory developed here, we prove that for any smooth bounded pseudoconvex domain with trivial Levi core the Diederich--Forn{ae}ss index is one and the $overline{partial}$-Neumann problem is exactly regular (via a result of Kohn and its generalization by Harrington). Our work builds on and expands recent results of Liu and Adachi--Yum.
We propose two constructions extending the Chern-Moser normal form to non-integrable Levi-nondegenerate (hypersurface type) almost CR structures. One of them translates the Chern-Moser normalization into pure intrinsic setting, whereas the other directly extends the (extrinsic) Chern-Moser normal form by allowing non-CR embeddings that are in some sense maximally CR. One of the main differences with the classical integrable case is the presence of the non-integrability tensor at the same order as the Levi form, making impossible a good quadric approximation - a key tool in the Chern-Moser theory. Partial normal forms are obtained for general almost CR structures of any CR codimension, in particular, for almost-complex structures. Applications are given to the equivalence problem and the Lie group structure of the group of all CR-diffeomorphisms.
We propose the concept of Diederich--Forn{ae}ss and Steinness indices on compact pseudoconvex CR manifolds of hypersurface type in terms of the DAngelo 1-form. When the CR manifold bounds a domain in a complex manifold, under certain additional non-degeneracy condition, those indices are shown to coincide with the original Diederich--Forn{ae}ss and Steinness indices of the domain, and CR invariance of the original indices follows.
This note establishes smooth approximation from above for J-plurisubharmonic functions on an almost complex manifold (X,J). The following theorem is proved. Suppose X is J-pseudoconvex, i.e., X admits a smooth strictly J-plurisubharmonic exhaustion function. Let u be an (upper semi-continuous) J-plurisubharmonic function on X. Then there exists a sequence {u_j} of smooth, strictly J-plurisubharmonic functions point-wise decreasing down to u. On any almost complex manifold (X,J) each point has a fundamental neighborhood system of J-pseudoconvex domains, and so the theorem above establishes local smooth approximation on X. This result was proved in complex dimension 2 by the third author, who also showed that the result would hold in general dimensions if a parallel result for continuous approximation were known. This paper establishes the required step by solving the obstacle problem.
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