The evolution and persistence of dumbbells

We use large-scale numerical simulations to study the formation and evolutionof non-topological defects in a generalized electroweak phase transitiondescribed by the Glashow-Salam-Weinberg model without fermions. Such defectsinclude dumbbells, comprising a pair of monopoles joined by a segment ofelectroweak string. These exhibit complex dynamics, with some shrinking underthe string tension and others growing due to the monopole-antimonopoleattractions between near neighbours. We estimate the range of parameters wherethe network of dumbbells persists, and show that this region is narrower thanthe region within which infinite straight electroweak strings areperturbatively stable.