First analytic correction beyond PFA for the electromagnetic field in sphere-plane geometry

We consider the vacuum energy for a configuration of a sphere in front of a plane, both obeying conductor boundary condition, at small separation. For the separation becoming small we derive the first next-to-leading order of the asymptotic expansion in the separation-to-radius ratio $\ep$. This correction is of order $\ep$. In opposite to the scalar cases it contains also contributions proportional to logarithms in first and second order, $\ep \ln \ep$ and $\ep (\ln \ep)^2$. We compare this result with the available findings of numerical and experimental approaches.