Transitions between topologically non-trivial configurations
  We study formation and evolution of solitons within a model with two real
scalar fields with the potential having a saddle point. The set of these
configurations can be split into disjoint equivalence classes. We give a simple
expression for the winding number of an arbitrary closed loop in the field
space and discuss the evolution scenarios that change the winding number. These
non-trivial field configurations lead to formation of the domain walls in the
three-dimensional physical space.
