Divergences in the vacuum energy for frequency-dependent interactions

We propose a method for determining ultra-violet divergences in the vacuum energy for systems whose spectrum of perturbations is defined through a non-linear spectrum problem, i.e, when the fluctuation operator itself depends on the frequency. The method is applied to the plasma shell model, which describes some properties of the interaction of electromagnetic field with fullerens. We formulate a scalar model, which simplifies the matrix structure, but keeps the frequency dependence of the plasma shell, and calculate the ultra-violet divergences in the case when the plasma sheet is slightly curved. The divergent terms are expressed in terms of surface integrals of corresponding invariants.