Vacuum fermionic currents in braneworld models on AdS bulk with a cosmic string

Abstract

We investigate the effects of a brane and magnetic-flux-carrying cosmic string on the vacuum expectation value (VEV) of the current density for a charged fermionic field in the background geometry of (4+1)-dimensional anti-de Sitter (AdS) spacetime. The brane is parallel to the AdS boundary and the cosmic string is orthogonal to the brane. Two types of boundary conditions are considered on the brane that include the MIT bag boundary condition and the boundary conditions in Z 2 -symmetric braneworld models. The brane divides the space into two regions with different properties of the vacuum state. The only nonzero component of the current density is along the azimuthal direction and in both the regions the corresponding VEV is decomposed into the branefree and brane-induced contributions. The latter vanishes on the string and near the string the total current is dominated by the brane-free part. At large distances from the string and in the region between the brane and AdS horizon the decay of the brane-induced current density, as a function of the proper distance, is power-law for both massless and massive fields. For a massive field this behavior is essentially different from that in the Minkowski bulk. In the region between the brane and AdS boundary the large-distance decay of the current density is exponential. Depending on the boundary condition on the brane, the brane-induced contribution is dominant or subdominant in the total current density at large distances from the string. By using the results for fields realizing two inequivalent irreducible representations of the Clifford algebra, the vacuum current density is investigated in C-and P -symmetric fermionic models. Applications are given for a cosmic string in the Randall-Sundrum-type braneworld model with a single brane.

Vacuum polarisation of Dirac fermions in the cosmological de Sitter-global monopole spacetime

“…The vacuum polarisation effects in the presence of a cosmic string is a much cultivated topic, both in flat and (anti)-de Sitter backgrounds. The study of the vacuum expectation values of the field squared, 0|φ 2 (x)|0 of a scalar field and of the fermionic condensate, 0|ψ(x)ψ(x)|0 , the vacuum expectation values of their energy-momentum tensors as well as of the conserved currents and various anomalies have extensively been investigated in [16]- [53]. Apart from the usual Minkowski, de Sitter/anti-de Sitter backgrounds, these studies also include spacetimes with compactified dimensions, and even the presence of a magnetic flux.…”