Casimir densities in brane models with compact internal spaces

Abstract

We investigate the Wightman function, the vacuum expectation values of the field squared and the energy-momentum tensor for a massive scalar field with general curvature coupling parameter subject to Robin boundary conditions on two codimension one parallel branes located on $(D+1)$-dimensional background spacetime $AdS_{D_{1}+1}\times \Sigma $ with a warped internal space $\Sigma $. The general case of different Robin coefficients on separate branes is considered. Unlike to the purely AdS bulk, the vacuum expectation values induced by a single brane, in addition to the distance from the brane, depends also on the position of the brane in the bulk. The brane induced parts in these expectation values vanish when the brane position tends to the AdS horizon or AdS boundary. For strong gravitational fields corresponding to large values of the AdS energy scale, the both single brane and interference parts of the expectation values integrated over the internal space are exponentially suppressed. An application to the higher dimensional generalization of the Randall-Sundrum brane model with arbitrary mass terms on the branes is discussed. For large distances between the branes the induced surface densities give rise to an exponentially suppressed cosmological constant on the brane.