Ground State Energy of Massive Scalar Field in the Background of Finite   Thickness Cosmic String
  We calculate the ground state energy of a massive scalar field in the background of a cosmic string of finite thickness (Gott-Hiscock metric). Using zeta functional regularization we discuss the renormalization and the relevant heat kernel coefficients in detail. The finite (non local) part of the ground state energy is calculated in 2+1 dimensions in the approximation of a small mass density of the string. By a numerical calculation it is shown to vanish as a function of the radius of the string and of the parameter $\xi$ of the nonconformal coupling. 
N.R. Khusnutdinov, M. Bordag