Long range Casimir force induced by transverse electromagnetic modes

We consider the interaction of two perfectly conducting plates of arbitrary shape that are inside a non-simply connected cylinder with transverse section of the same shape. We show that the existence of transverse electromagnetic (TEM) modes produces a Casimir force that decays only as $1/a^2$, where $a$ is the distance between plates. The TEM force does not depend on the area of the plates and dominates at large distances over the force produced by the transverse electric (TE) and transverse magnetic (TM) modes, providing in this way a physical realization of the 1+1 dimensional Casimir effect. For the particular case of a coaxial circular cylindrical cavity, we compute the TE, TM and TEM contributions to the force, and find the critical distance for which the TEM modes dominate.