Boundary regularity for the\bar \partial _b - Neumann problem, part 1problem, part 1

We establish sharp regularity and Fredholm theorems for the operator on domains satisfying some nongeneric geometric conditions. We use these domains to construct explicit examples of bad behavior of the Kohn Laplacian: It is not always hypoelliptic up to the boundary, its partial inverse is not compact and it is not globally subelliptic.     

L 2 existence theorems for the\bar \partial _b - Neumann problem on strongly pseudoconvex CR manifoldsproblem on strongly pseudoconvex CR manifolds

LetM be the boundary of a strongly pseudoconvex domain in \(\mathbb{C}^n \) ,n≥4 and ω be an open subset inM such that ?ω is the intersection ofM with a flat hypersurface. We establish theL ² existence theorems of the \(\bar \partial _b - Neumann\) problem on ω. In particular, we prove that the \(\bar \partial _b - Laplacian\) \(\square _b = \bar \partial _b \bar \partial _b^* + \bar \partial _b^* \bar \partial _b \) equipped with a pair of natural boundary conditions, the so-called \(\bar \partial _b - Neumann\) boundary conditions, has closed range when it acts on (0,q) forms, 1≤q≤n?3. Thus there exists a bounded inverse operator for \(\square _b \) , the \(\bar \partial _b - Neumann\) operatorN _b, and we have the following Hodge decomposition theorem on ω for \(\bar \partial _b \bar \partial _b^* N_b \alpha + \bar \partial _b^* \bar \partial _b N_b \alpha \) , for any (0,q) form α withL ²(ω) coefficients. The proof depends on theL ^p regularity of the tangential Cauchy-Riemann operators \(\bar \partial _b u = \alpha \) on ω?M under the compatibility condition \(\bar \partial _b \alpha = 0\) , where α is a (p, q) form on ω, where 1≤q≤n?2. The interior regularity ofN _b follows from the fact that \(\square _b \) is subelliptic in the interior of ω. The operatorN _b induces natural questions on the regularity up to the boundary ?ω. Near the characteristic point of the boundary, certain compatibility conditions will be present. In fact, one can show thatN _b is not a compact operator onL ²(ω).     

Intrinsic Lipschitz classes on manifolds with applications to complex function theory and estimates for the\bar \partial and\bar \partial _b equations

An intrinsic definition of Lipschitz classes in terms of vector fields on man-ifolds is provided and it is shown that it is locally equivalent with a more classical definition. A finer result is then proved for strongly pseudo-convex CR manifolds and applications of the theorems are given to smoothness of holomorphic functions and estimates for the \(\bar \partial \) and \(\bar \partial _b \) . equations.     

Uniform estimates with weights for the\bar \partial - equation

This paper concernsL ^∞-variants of Hörmanders weightedL ²-estimates for the $\bar \partial - equation$ . In particular, we discuss a conjecture concerning suchL ^∞-estimates which is related to the corona problem in the ball, and show a weaker version of this conjecture. The proof uses a refinedL ²-estimate for the canonical solution to the $\bar \partial - equation$ . An alternative approach based on von Neumann’s Minimax theorem is also given.     

Local existence theorems with estimates for\bar \partial _b on weakly pseudo-convex CR manifolds

Partially supported by NSF grants DMS 89-01455 and DMS 91-01161     

A division problem for\bar \partial _b - CLOSED forms

LetG ₁,…,G_m be bounded holomorphic functions in a strictly pseudoconvex domainD such that . We prove that for each (0,q)-form ϕ inL ^p(∂D), 1<p<∞, there are formsu ₁, …,u _m inL ^p(∂D) such that ΣG _ju_j=ϕ. This generalizes previous results forq=0. The proof consists in delicate estimates of integral representation formulas of solutions and relies on a certainT1 theorem due to Christ and Journé. For (0,n−1)-forms there is a simpler proof that also gives the result forp=∞. Restricted to one variable this is precisely the corona theorem. The author was partially supported by the Swedish Natural Research Council.     

Estimates for integral kernels of mixed type,fractional integration operators,and optimal estimates for the\bar \partial operator

Sharp tangential Lipschitz estimates for the inhomogeneous Cauchy Riemann equations with L^p data on strongly pseudoconvex doma ins in complex manifolds are proved. Estimates in both isotropic and non-isotropic spaces of functions of bounded mean oscillation are proved.Tangential estimates for a large class of domains are shown to follow from those on the ball.In the course of the proofs a fractional integration theorem of independent interest is proved.This work was partially supported by NSF Grant # MCB 77-02213     

Regularity of\bar \partial _b , complex on nondegenerate Cauchy-Riemann manifolds, complex on nondegenerate Cauchy-Riemann manifolds

For each point ξ in a CR manifold M of codimension greater than 1, the CR structure of M can be approximated by the CR structure of a nilpotent Lie group G_ξ of step two near ξ. G_ξ varies with ξ. $\square _b $ and $\bar \partial _b $ on M can be approximated by $\square _b $ and $\bar \partial _b $ on the nilpotent Lie group G_ξ We can construct the parametrix of $\square _b $ on M by using the parametrix of $\square _b $ on nilpotent group of step two, and define a quasidistance on M by the approximation. The regularity of $\square _b $ and $\bar \partial _b $ follows from the Harmonic analysis on M.     

Sharp estimates for\bar \partial on convex domains of finite typeon convex domains of finite type

Let Ω be a bounded convex domain in C _n , with smooth boundary of finite typem. The equation is solved in Ω with sharp estimates: iff has bounded coefficients, the coefficients of our solutionu are in the Lipschitz space Λ. Optimal estimates are also given when data have coefficients belonging toL ^p(Ω),p≥1. We solve the -equation by means of integral operators whose kernels are not based on the choice of a “good” support function. Weighted kernels are used; in order to reflect the geometry ofbΩ, we introduce a weight expressed in terms of the Bergman kernel of Ω.     

Necessary geometric and analytic conditions for general estimates in the $\bar{\partial}$-Neumann problem

We show the geometric and analytic consequences of a general estimate in the \(\bar{\partial}\)-Neumann problem: a “gain” in the estimate yields a bound in the “type” of the boundary, that is, in its order of contact with an analytic curve as well as in the rate of the Bergman metric. We also discuss the potential-theoretical consequence: a gain implies a lower bound for the Levi form of a bounded weight.     

Unique continuation theorems for the\bar \partial - Operator and applications

We formulate a unique continuation principle for the inhomogeneous Cauchy-Riemann equations near a boundary pointz ₀ of a smooth domain in complex euclidean space. The principle implies that the Bergman projection of a function supported away fromz ₀ cannot vanish to infinite order atz ₀ unless it vanishes identically. We prove that the principle holds in planar domains and in domains where the problem is known to be analytic hypoelliptic. We also demonstrate the relevance of such questions to mapping problems in several complex variables. The last section of the paper deals with unique continuation properties of the Szegő projection and kernel in planar domains. Research supported by NSF Grant DMS-8922810.     

Fast-decaying potentials on the finite-gap background and the\bar \partial - problem on the Riemann surfaces

The direct and the inverse scattering problems for the heat-conductivity operator are studied for the following class of potentials:u(x,y)=u _o (x,y)+u ₁(x,y), whereu _o (x,y) is a nonsingular real finite-gap potential andu ₁(x,y) decays sufficiently fast asx ²+y². We show that the scattering data for such potentials is the data on the Riemann surface corresponding to the potentialu _o (x,y). The scattering data corresponding to real potentials is characterized and it is proved that the inverse problem corresponding to such data has a unique nonsingular solution without the small norm assumption. Analogs of these results for the fixed negative energy scattering problem for the two-dimensional time-independent Schrödinger operator are obtained.L. D. Landau Institute for Theoretical Physics, Kosygina 2, GSP-1, Moscow 177940, Russia. E-mail: pgg@cpd.landau.free.net. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 99, No. 2, pp. 300–308, May, 1994.