We show that the double cobar construction, $\Omega^2 C_*(X)$, of a simplicial set $X$ is a homotopy BV-algebra if $X$ is a double suspension, or if $X$ is 2-reduced and the coefficient ring contains the ring of rational numbers $\mathbb{ Q}$. Indeed, the Connes-Moscovici operator defines the desired homotopy BV-algebra structure on $\Omega^2 C_*(X)$ when the antipode $S : \Omega C_*(X) \to \Omega C_*(X)$ is involutive. We proceed by defining a family of obstructions $O_n : \widetilde{ C}_*(X) \to \widetilde{ C}_*(X)^{ \otimes n}$, $n\geq 2$ measuring the difference $S^2 - Id$. When $X$ is a suspension, the only obstruction remaining is $O_2 := E^{ 1,1} - \tau E^{ 1,1}$ where $E^{ 1,1}$ is the dual of the $\smile_1$-product. When $X$ is a double suspension the obstructions vanish.
Categories: math.AT
