  The renormalized mean value of the quantum Lagrangian and the Energy-Momentum
tensor for scalar fields coupled to an arbitrary gravitational field
configuration are analytically evaluated in the Schwinger-DeWitt approximation,
up to second order in the inverse mass value. The cylindrical symmetry
situation is considered. The results furnish the starting point for
investigating iterative solutions of the back-reaction problem related with the
quantization of cylindrical scalar field configurations. Due to the homogeneity
of the equations of motion of the Klein-Gordon field, the general results are
also valid for performing the quantization over either vanishing or
non-vanishing mean field configurations. As an application, compact analytical
expressions are derived here for the quantum mean Lagrangian and
Energy-Momentum tensor in the particular background given by the Black-String
space-time.
