The method of layer potentials in $L^p$ and endpoint spaces for elliptic operators with $L^{\mathrm{\infty }}$ coefficients

We consider layer potentials associated to elliptic operators $Lu=-{\rm div}(A \nabla u)$actingintheupperhalf-space$$\mathbb{R}$^{n+1}_+$for$n\geq 2$, or more generally, in a Lipschitz graph domain, where the coefficient matrix $A$ is $L^{\mathrm{\infty }}$ and $t$-independent, and solutions of $Lu=0$ satisfy interior estimates of De Giorgi/Nash/Moser type. A “Calder'on-Zygmund” theory is developed for the boundedness of layer potentials, whereby sharp $L^p$ and endpoint space bounds are deduced from $L^2$ bounds. Appropriate versions of the classical “jump-relation” formulae are also derived. The method of layer potentials is then used to establish well-posedness of boundary value problems for $L$ with data in $L^p$ and endpoint spaces.