Exact solution to a new anisotropic dimer model with domain-wall behavior

The exact solution is given for the thermal behavior of a dimer model that has two kinds of infinite energy excitations that can be described as heavy and light domain walls in a 2×{}1 adsorbed-atom model. These walls may reverse their direction with respect to the anisotropy axis and, upon meeting, unlike walls may annihilate. In the general case there are three phases and the intermediate phase is an incommensurate phase with a difference in population of the two kinds of walls. A further generalization of the model is given in which like walls may also annihilate.