Gravitational Effects of Quantum Fields in the Interior of a Cylindrical Black Hole

The gravitational back-reaction is calculated for the conformally invariant scalar field within a black cosmic string interior with cosmological constant. Using the perturbed metric, the gravitational effects of the quantum field are calculated. It is found that the perturbations initially weaken the singularity. This effect differs from the case of spherical symmetry (without cosmological constant) where the singularity is initially strengthened. This indicates that the behaviour of quantum effects may not be universal but instead depend on the geometry of the spacetime as well as whether or not there exists a non-zero cosmological constant. PACS number(s): 04.70.-s, 95.30.Sf