Quantum fluctuation of stress tensor in a higher-derivative scalar field theory around a cosmic string

In this paper, we calculate the vacuum fluctuation of the stress tensor of a higher-derivative theory around a thin cosmic string. To this end, we adopt the method to obtain the stress tensor from the effective action developed by Gibbons et al. By their method, the quantum stress tensor of higher-derivative scalar theories without self-interaction is expressed as a simple sum of quantum stress tensors of free massive scalar fields. Unlike the vacuum expectation value of the scalar field squared obtained in the similar model, there appears no reduction of the values near the conical singularity.

Quantum stress tensor of massive vector field in the spacetime of a pointlike global monopole

The components of the renormalized quantum stress tensor for a massive vector field in the spacetime of a pointlike global monopole are determined analytically in the Schwinger–DeWitt approximation. The general results are employed to investigate the pointwise energy conditions for the quantized matter field and it is shown that they are all violated by the massive vector field.