Green's Function Estimates for Elliptic Differential Operators with Singular Coefficients and Absolute Convergence of Fourier Series

Let $\Omega$ be a smooth bounded domain in $\mathbb{R}^n$, and let $A$ be a linear elliptic differential operator of order $2m$ with singular coefficients acting in $L^2(\Omega)$. Under some assumptions of singularity for the coefficients of $A$, we obtain Green's function estimates that hold up to the boundary of the domain and study the absolute convergence of the corresponding Fourier series.