Surface Casimir densities and induced cosmological constant in higher dimensional braneworlds

TL;DR

This paper analyzes the vacuum expectation value of surface energy-momentum tensors in higher-dimensional warped spacetimes with branes, revealing how brane separation influences induced cosmological constants.

Contribution

It introduces a method to compute surface energies in higher-dimensional braneworlds with Robin boundary conditions, including effects of a second brane and asymptotic behaviors.

Findings

Surface densities are finite for nonzero brane separation.

Large interbrane distances exponentially suppress the induced cosmological constant.

Pole parts cancel in odd spatial dimensions, yielding finite total zeta functions.

Abstract

We investigate the vacuum expectation value of the surface energy-momentum tensor for a massive scalar field with general curvature coupling parameter obeying the Robin boundary conditions on two codimension one parallel branes in a (D+1)-dimensional background spacetime $AdS_{D_{1}+1}\times \Sigma $ with a warped internal space $\Sigma $. These vacuum densities correspond to a gravitational source of the cosmological constant type for both subspaces of the branes. Using the generalized zeta function technique in combination with contour integral representations, the surface energies on the branes are presented in the form of the sum of single brane and second brane induced parts. For the geometry of a single brane both regions, on the left and on the right of the brane, are considered. At the physical point the corresponding zeta functions contain pole and finite contributions. For an infinitely thin brane taking these regions together, in odd spatial dimensions the pole parts cancel and the total zeta function is finite. The renormalization procedure for the surface energies and the structure of the corresponding counterterms are discussed. The parts in the surface densities generated by the presence of the second brane are finite for all nonzero values of the interbrane separation and are investigated in various asymptotic regions of the parameters. In particular, it is shown that for large distances between the branes the induced surface densities give rise to an exponentially suppressed cosmological constant on the brane. The total energy of the vacuum including the bulk and boundary contributions is evaluated by the zeta function technique and the energy balance between separate parts is discussed.