The string solution in SU(2) Yang-Mills-Higgs theory
  The tube solutions in Yang - Mills - Higgs theory are received, in which the Higgs field has the negative energy density. This solutions make up the discrete spectrum numered by two integer and have the finite linear energy density. Ignoring its transverse size, such field configuration is the rest infinity straight string. 
Vladimir Dzhunushaliev and Alexej Fomin