  Vortices in superfluid 3He-B have been observed to undergo a core transition.
We discuss the analog phenomenon in relativistic field theories which admit
embedded global domain walls, vortices and monopoles with a core phase
structure. They are present in scalar field theories with approximate global
symmetries which are broken both spontaneously and in parts explicitly. For a
particular range of parameters their symmetric core exhibits an instability and
decays into the nonsymmetric phase.
