Topologically Stable Electroweak Flux Tube

We show that for a large range of parameters in a $SU(2)_L\times U(1)$ electroweak theory with two Higgs doublets there may exist classically stable flux tubes of Z boson magnetic field. In a limit of an extra global $\tilde U(1)$ symmetry, these flux-tubes become topologically stable. These results are automatically valid even if $\tilde U(1)$ is gauged.Comment: 10 pages, LATE