Grothendieck--Teichm\"uller Symmetries of Cyclic Operads and Tangles

Abstract

We characterise the profinite Grothendieck-Teichm\"uller group $\widehat{\mathsf{GT}}$ as the group of automorphisms of the profinite completion of a cyclic operad of parenthesised ribbon braids. This operad generates a symmetric monoidal category which is equivalent to the category of framed, oriented tangles, thereby providing an operadic model for profinite tangles and their arithmetic symmetries. As applications, we show that $\widehat{\mathsf{GT}}$ acts naturally on tangles and provide an alternative proof of the formality of the cyclic framed little disks operad.