Static and dynamical Casimir effects in a wedge within the worldline formulation

Abstract

We study a real massless scalar field in $d+1$ dimensions confined to a wedge of opening angle $α$, in the presence of a semitransparent circular arc that may oscillate radially. Within the worldline formulation, and for an arbitrary strength $λ$ of the $δ$-potential that models the arc, we expand the effective action in powers of the radial displacement $R$ of the arc. In this formulation, all the information about the media is contained in the propagator of a non-relativistic point particle, so that known results for that propagator can be used directly. At zeroth order we obtain the Casimir energy of the wedge, with Dirichlet, Neumann or mixed walls, and the contribution of the arc in closed form for arbitrary $λ$. We show that the worldline integrand is, point by point, the energy density obtained from the energy-momentum tensor of the scalar field with curvature coupling $ξ=1/4$; with this identification, and using dimensional regularization for the integrated quantities, we recover the known results for the wedge and for the wedge closed by a Dirichlet arc. At second order in $R$, we reduce the form factor that determines the imaginary part of the in-out effective action, and hence the probability of pair creation by the moving arc, to a one-loop expression involving the radial Green's functions of each angular sector. In the narrow-wedge limit, each angular sector behaves as a field with a mass set by the angular quantization, coupled to a moving $δ$-mirror; for a Dirichlet arc, the pair creation spectrum of the exterior region approaches that of a planar massive mirror, while the interior region behaves as a tapered cavity. Finally, by decomposing the electromagnetic field into TE and TM scalars, we obtain the Casimir energy of wedges with perfectly conducting, perfectly permeable and mixed walls.