Every unitary solution of the Yang-Baxter equation (R-matrix) in dimension d can be viewed as a unitary element of the Cuntz algebra O d and as such defines an endomorphism of O d . These Yang-Baxter endomorphisms restrict and extend to endomorphisms of several other C * -and von Neumann algebras and furthermore define a II 1 factor associated with an extremal character of the infinite braid group. This paper is devoted to a detailed study of such Yang-Baxter endomorphisms.Among the topics discussed are characterizations of Yang-Baxter endomorphisms and the relative commutants of the various subfactors they induce, an endomorphism perspective on algebraic operations on R-matrices such as tensor products and cabling powers, and properties of characters of the infinite braid group defined by R-matrices. In particular, it is proven that the partial trace of an R-matrix is an invariant for its character by a commuting square argument.Yang-Baxter endomorphisms also supply information on R-matrices themselves, for example it is shown that the left and right partial traces of an R-matrix coincide and are normal, and that the spectrum of an R-matrix can not be concentrated in a small disc. Upper and lower bounds on the minimal and Jones indices of Yang-Baxter endomorphisms are derived, and a full characterization of R-matrices defining ergodic endomorphisms is given.As examples, so-called simple R-matrices are discussed in any dimension d, and the set of all Yang-Baxter endomorphisms in d = 2 is completely analyzed.
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