# Name for an Isomorphism in a Monoidal Category that Satisfies the Braid Relation

Let $({\cal C},\otimes)$ be a monoidal category, $X$ an object in ${\cal C}$, and $\Psi:X \otimes X \to X \otimes X$ an isomorphism such that $\Psi$ satisfies the braid relation: $$(\Psi \otimes \text{id}) \circ (\text{id} \otimes \Psi) \circ (\Psi \otimes \text{id}) = (\text{id} \otimes \Psi) \circ (\Psi \otimes \text{id}) \circ (\text{id} \otimes \Psi).$$ What would one call such an isomorphism? The most obvious suggestion is to call it a braiding for $X$. Might this be taken to imply that $\Psi$ comes from a braiding for the category (which I do not want to assume)?

• I think you can just call it a braiding. You might just add in a disclaimer to say that you are not assuming that the category itself is braided. I don't think I have ever heard another term used for a map satisfying that relation. – MTS Oct 21 '11 at 16:27
• Are you sure you don't want $\Psi$ to be an automorphism of $X \otimes X$? – S. Carnahan Oct 21 '11 at 16:39
• Yes, of course. – Réamonn Ó Buachalla Oct 21 '11 at 17:19
• It is a braiding on the subcategory it generates... – Noah Snyder Oct 21 '11 at 17:24

Assuming S. Carnahan's surmise in his comment is correct, I believe the correct term for this is "Yang-Baxter" operator in a monoidal category (or, you could call an object $X$ equipped with such an automorphism $R: X \otimes X \to X \otimes X$ a Yang-Baxter object). This terminology is given in the seminal paper on the subject, Braided Tensor Categories by Joyal and Street (Adv. Math. 102, pp. 20-78, 1993).