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arXiv math/0601307math.AP
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具有退化系数的二阶算子

Second-order operators with degenerate coefficients

A. F. M. ter Elst, Derek W. Robinson, Adam Sikora, Yueping Zhu

摘要:

本文研究了$\Ri^d$上二阶算子$H = -\sum^d_{i,j=1} \partial_i \, c_{ij} \, \partial_j$的性质,其中二阶算子具有有界实对称可测系数.我们假设$C = (c_{ij}) \geq 0$几乎处处成立,但也考虑到$C$可能是单数。我们将一个正则自伴粘性算子$H_0$与$H$联系起来,并研究了由$H_0$生成的粘性半群$S^{(0)}$的性质.该半群在具有$p \in [1,\infty]$的$L_p$ -空间上扩张为正压缩半群.我们建立了它保持概率,满足$L_2$ ~非对角边界和与$H_0$相关的波动方程具有有限的传播速度。然而,$S^{(0)}$并不总是严格正的,因为即使对于亚椭圆算子,系统的分离也会发生。这证明了次椭圆半群一般不是遍历的,它们的核既不是严格正的也不是Hölder连续的。特别是,即使使用带有$\varepsilon > 0$的$C^{2-\varepsilon}(\Ri^d)$中的系数,也可以构造高斯上限和下限均失败的示例。

英文摘要:

We consider properties of second-order operators $H = -\sum^d_{i,j=1} \partial_i \, c_{ij} \, \partial_j$ on $\Ri^d$ with bounded real symmetric measurable coefficients. We assume that $C = (c_{ij}) \geq 0$ almost everywhere, but allow for the possibility that $C$ is singular. We associate with $H$ a canonical self-adjoint viscosity operator $H_0$ and examine properties of the viscosity semigroup $S^{(0)}$ generated by $H_0$. The semigroup extends to a positive contraction semigroup on the $L_p$-spaces with $p \in [1,\infty]$. We establish that it conserves probability, satisfies $L_2$~off-diagonal bounds and that the wave equation associated with $H_0$ has finite speed of propagation. Nevertheless $S^{(0)}$ is not always strictly positive because separation of the system can occur even for subelliptic operators. This demonstrates that subelliptic semigroups are not ergodic in general and their kernels are neither strictly positive nor Hölder continuous. In particular one can construct examples for which both upper and lower Gaussian bounds fail even with coefficients in $C^{2-\varepsilon}(\Ri^d)$ with $\varepsilon > 0$.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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