Operator-norm resolvent asymptotic analysis of continuous media with low-index inclusions

Using a generalisation of the classical notion of Dirichlet-to-Neumann map and the related formulae for the resolvents of boundary-value problems, we analyse the asymptotic behaviour of solutions to a transmission for a high-contrast inclusion in a continuous medium, for which we prove the operator-norm resolvent convergence to a limit problem of electrostatic type for functions that are constant on the inclusion. In particular, our results imply the convergence of the spectra of high-contrast problems to the spectrum of the limit operator, with order-sharp convergence estimates.