A general functional definition of the infinite dimensional quantum
R-matrix satisfying the Yang-Baxter equation is given. A procedure for the extracting a finite dimensional
R-matrix from the general definition is demonstrated in a particular case when the group
SU(2) takes place.
A parametrized Yang-Baxter equation is usually defined to be a map from a group to a set of R-matrices, satisfying the Yang-Baxter commutation relation. These are a mainstay of solvable lattice models. We will show how the parameter space can sometimes be enlarged to a groupoid, and give two examples of such groupoid parametrized Yang-Baxter equations, within the six vertex model. A groupoid parametrized Yang-Baxter equation consists of a groupoid
G together with a map
π:G→End(V⊗V) for some vector space
V such that the Yang-Baxter commutator
[[π(u),π(w),π(v)]]=0 if
u,v∈G are such that the groupoid composition
w=u⋆v is defined. An important role is played by an object map
Δ:G→M for some set
M such that
Δ(u)=Δ(v′),
Δ(w)=Δ(v) and
Δ(w′)=Δ(u′), where
v↦v′ is the groupoid inverse map. There are two main regimes of the six-vertex model: the free-fermionic point, and everything else. For the free-fermionic point, there exists a parametrized Yang-Baxter equation with a large parameter group
GL(2)×GL(1). For non-free-fermionic six-vertex matrices, there are also well-known (group) parametrized Yang-Baxter equations, but these do not account for all possible interactions. Instead we will construct a groupoid parametrized Yang-Baxter equation that accounts for essentially all possible Yang-Baxter equations in the six-vertex model. We will also exhibit a separate groupoid for the five-vertex model. We will show how to construct solvable lattice models based on groupoid parametrized Yang-Baxter equations.