Fundamental solutions for second order subelliptic operators (Q1088840)

This paper deals with the fundamental solution of a second-order linear partial differential operator L on a compact manifold M with smooth measure \(\mu\). In local coordinates \[ L=- \sum^{n}_{i,j=1}a^{ij}(x)\partial x_ i\partial x_ j+\sum^{n}_{k=1}b^ k(x)\partial x_ k+c(x), \] where \((a^{ij})\), \((b^ k)\), c are real, \(n>2\), the matrix \((a^{ij}(x))\) is positive semidefinite, and L is subelliptic. The author investigates the behavior of the fundamental solution G(x,y) near \(x=y\) and finds out its estimates. Furthermore, the author gets some new estimates for solution of the equation \(Lu=f\).