where is one of the spatial variables ( is taken to be independent of , and the remaining spatial variables). The solution interpolates between the two different vacua of the double well potential. It is not possible to deform the kink into a constant solution without passing through a solution of infinite energy, and for this reason the kink is said to be stable. For "D">2 (i.e., theories with more than one spatial dimension), this solution is called a domain wall.