A variational approach to $S^1$-harmonic maps and applications

We present a renormalization procedure of the Dirichlet Lagrangian for maps from surfaces with or without boundary into $S^1$ and whose finite energy critical points are the $S^1-$harmonic maps with isolated singularities. We give some applications of this renormalization scheme in two different frameworks. The first application has to do with the renormalization of the Willmore energy for Lagrangian singular immersions into K"ahler-Einstein Surfaces while the second application is dealing with frame energies for surfaces immersions into Euclidian spaces.