Electroweak Strings and Fermions
Kono, Shion, Stephen G. Naculich · arXiv (Cornell University) · 1995
Z-strings in the Weinberg-Salam model including fermions are unstable for all values of the parameters. The cause of this instability is the fermion vacuum energy in the Z-string background. Z-strings with non-zero fermion densities, however, may still be stable.