Vacuum Structure and Global Strings with Conical Singularities
  Vacuum structure and global cosmic strings are analyzed in the effective theory of self-interacting O(2) scalar fields on (3+1)-manifolds with conical singularities. In the context of one-loop effective action computed by heat-kernel methods with $\zeta$-function regularization, we find an inhomogeneous vacuum of minimum energy and suggest some reason why low-energy global strings are likely to be generated at the conical singularities. 
Yoonbai Kim, O-Kab Kwon, Jongsu Sohn