  Minimum Riesz energy problems in the presence of an external field are
analyzed for a condenser with touching plates. We obtain sufficient and/or
necessary conditions for the solvability of these problems in both the
unconstrained and the constrained settings, investigate the properties of
minimizers, and prove their uniqueness. Furthermore, characterization theorems
in terms of variational inequalities for the weighted potentials are
established. The results obtained are illustrated by several examples.
