Yang-Baxter equation
Yang-Baxter equation 1968, 1971
In physics, the YangâBaxter equation (or starâtriangle relation) is a consistency equation which was first introduced in the field of statistical mechanics. It depends on the idea that in some scattering situations, particles may preserve their momentum while changing their quantum internal states. It states that a matrix $${R}$$, acting on two out of three objects, satisfies
- $${ ({\check {R}}\otimes \mathbf {1} )(\mathbf {1} \otimes {\check {R}})({\check {R}}\otimes \mathbf {1} )=(\mathbf {1} \otimes {\check {R}})({\check {R}}\otimes \mathbf {1} )(\mathbf {1} \otimes {\check {R}})}$$
In one dimensional quantum systems, $${R}$$ is the scattering matrix and if it satisfies the YangâBaxter equation then the system is integrable. The YangâBaxter equation also shows up when discussing knot theory and the braid groups where $${R}$$ corresponds to swapping two strands. Since one can swap three strands two different ways, the YangâBaxter equation enforces that both paths are the same.