In this paper we utilize ζ-function regularization techniques in order to compute the Casimir force for massless scalar fields subject to Dirichlet and Neumann boundary conditions in the setting of the conical piston. The piston geometry is obtained by dividing the bounded generalized cone into two regions separated by its cross section positioned at a with a ∈ (0, b) with b > 0. We obtain expressions for the Casimir force that are valid in any dimension for both Dirichlet and Neumann boundary conditions in terms of the spectral ζ-function of the piston. As a particular case, we specify the piston to be a d-dimensional sphere and present explicit results for d = 2, 3, 4, 5.
I. INTRODUCTIONThe Casimir effect is one of the most important macroscopic manifestations of the zero point energy of quantized fields under the influence of external conditions [11,38] or in spaces with non-trivial topology. In recent years, a vast amount of literature has been produced on the Casimir effect, which was first predicted in the seminal paper [13], especially for its relevance in nanoscale physics [10,11,38]. Due to its nature, calculations of the vacuum energy lead to divergencies which need to be regularized and subsequently renormalized. Several regularization methods exist, amongst the most important ones are frequency cutoff, point splitting and zeta function regularization [6,10,12,22,23,38]. For many configurations, these techniques yield the same finite renormalized result, however the way divergencies are removed is different in each scheme. The non-uniqueness of the removal procedure raises the question, which of them is the physically best motivated one. Technical and interpretational problems of this nature can actually be avoided if one considers the Casimir effect between separate objects. In this case, the divergent part of the energy (for massless fields) depends on the heat kernel coefficient a D/2 related to the geometry of the objects.These coefficients, in turn, do not depend on the distance between the bodies and, hence, the Casimir force between them is free of divergencies [10]. Belonging to the class of configurations for which the Casimir force has been unambiguously evaluated are pistons of certain types.These piston configurations, introduced in [14], have become increasingly important because of this fact. A large variety of piston configurations and boundary conditions have been studied throughout the lit- *