### Casimir forces in cavities with a finite plasma
frequency

**Jordan Maclay**

*Quantum Fields LLC*

*Richland Center WI 53581*

**Carlos Villarreal**

*Institute de Fisica*

*Universidad Autonoma de Mexico*

*Apartado Postal 20-364*

*Mexico, 01000, D.F.*

We extend previous calculations of the Casimir forces in perfectly
conducting rectangular cavities in order to consider finite conductivity
by including an exponential cutoff in the frequency. We study
the renormalized stress energy tensor of the system as an explicit
function of the cutoff frequency and the cavity geometry. As in
the case of perfectly conducting cavities, we predict changes
in the sign and magnitude of the force as the geometry of the
cavity is modified. In particular, repulsive forces are predicted,
even for cavities with a finite plasma frequency, but the transition
from attractive to repulsive forces occurs for deeper cavities,
making experiments more difficult.