  In this paper we consider a massive vector field in the background of a
space-time obtained by certain Z2 quotient of the BTZ black hole. We analyse
the back reaction of the matter field on the space-time geometry up to first
order in metric perturbation. The expectation value of the stress-energy tensor
can be computed exactly by considering its pull-back onto the covering space.
Upon a suitable choice of the boundary condition on the vector field around a
non-contractible cycle of the quotient manifold it is possible to obtain the
average energy on a null geodesic to be negative there by resulting a
traversable wormhole.
