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arXiv 2302.02746math.AP
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二阶椭圆算子的临界扰动。部分II:非切向极大函数估计

Critical Perturbations for Second Order Elliptic Operators. Part II: Non-tangential maximal function estimates

Simon Bortz, Steve Hofmann, José Luis Luna Garcia, Svitlana Mayboroda, Bruno Poggi

摘要:

本文是用层势方法研究二阶椭圆算子$-\operatorname{div} A \nabla$的一阶和零阶摄动的最后一部分,这些摄动的复系数位于临界空间.特别是,我们证明了$L^2$适定性(自然非切极大函数估计)的Dirichlet,Neumann和正则性问题的复杂的埃尔米特,块形式,或常数系数散度型椭圆算子在上半空间都是稳定的扰动下。由于缺乏经典的De Giorgi-Nash-Moser理论在我们的设置,我们的方法来证明非切极大函数估计依赖于一个全新的参数:我们得到了一定的弱$L^p$ "PDMATHAMP"估计,我们最终耦合平方函数界,加权外推理论,和自举参数恢复完整的$L^2$界。最后,我们证明了在一个相对广泛的类的解的存在性和唯一性。作为推论,我们要求的第一个结果在无界域有关的$L^p$ -可解性的边值问题的磁薛定谔算子$-(\nabla-i{\bf a})^2+V$时,磁位${\bf a}$和电位$V$相应地小尺度不变的勒贝格空间的范数。

英文摘要:

This is the final part of a series of papers where we study perturbations of divergence form second order elliptic operators $-\operatorname{div} A \nabla$ by first and zero order terms, whose complex coefficients lie in critical spaces, via the method of layer potentials. In particular, we show that the $L^2$ well-posedness (with natural non-tangential maximal function estimates) of the Dirichlet, Neumann and regularity problems for complex Hermitian, block form, or constant-coefficient divergence form elliptic operators in the upper half-space are all stable under such perturbations. Due to the lack of the classical De Giorgi-Nash-Moser theory in our setting, our method to prove the non-tangential maximal function estimates relies on a completely new argument: We obtain a certain weak-$L^p$ ''$N<S$'' estimate, which we eventually couple with square function bounds, weighted extrapolation theory, and a bootstrapping argument to recover the full $L^2$ bound. Finally, we show the existence and uniqueness of solutions in a relatively broad class. As a corollary, we claim the first results in an unbounded domain concerning the $L^p$-solvability of boundary value problems for the magnetic Schrödinger operator $-(\nabla-i{\bf a})^2+V$ when the magnetic potential ${\bf a}$ and the electric potential $V$ are accordingly small in the norm of a scale-invariant Lebesgue space.

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