Invariant Hopf $2$-cocycles for affine algebraic groups

We generalize the theory of the second invariant cohomology group $H^2_{\rm inv}(G)$forfinitegroups$G$, developed in [Da2,Da3,GK], to the case of affine algebraic groups $G$, using the methods of [EG1,EG2,G]. In particular, we show that for connected affine algebraic groups $G$ over an algebraically closed field of characteristic $0$, the map $\mathrm{\Theta }$ from [GK] is bijective (unlike for some finite groups, as shown in [GK]). This allows us to compute $H_{\mathrm{i}\mathrm{n}\mathrm{v}}^2(G)$ in this case, and in particular show that this group is commutative (while for finite groups it can be noncommutative, as shown in [GK]).